What type of bond is present in Grignard reagents?
Click to see answer
A polarized carbon-magnesium bond.
Click to see question
What type of bond is present in Grignard reagents?
A polarized carbon-magnesium bond.
What are the two names for CH3I?
Iodomethane and methyl iodide.
What geometric arrangement is required for E2 reactions?
Periplanar geometry.
What are the two main reactions that alkyl halides undergo with nucleophiles or bases?
Substitution of the X group by the nucleophile and elimination of HX by the base to yield an alkene.
What is formed during the S N 1 reaction?
A carbocation intermediate and an ion-pair.
Which atoms must lie in the same plane during an E2 reaction?
The hydrogen, the two carbons, and the leaving group.
What is produced during the elimination reaction of alkyl halides?
An alkene is produced by the elimination of HX.
Rank the following in terms of nucleophilicity from most to least: OH-, CH3CO2-, H2O.
OH- > CH3CO2- > H2O.
What reagents are commonly used to convert HO– into a better leaving group for S N 2 reactions?
SOCl2 or PBr3.
What are the two characteristics of the carbon atom in Grignard reagents?
It is both nucleophilic and basic.
What type of activity does Halomon exhibit?
Anticancer activity against several human tumor cell lines.
What type of intermediate is formed during the S N 1 reaction?
Carbocation intermediate.
Which components participate in the rate-limiting step of E2 reactions?
Both base and alkyl halide.
How stable are secondary allylic and secondary benzylic carbocations compared to tertiary alkyl carbocations?
They are about as stable as tertiary alkyl carbocations.
How are alkyl halides involved in biochemical pathways of terrestrial organisms?
They are not often involved, but their reactions are frequently involved.
What naming convention will not be used in this textbook?
Names shown in parentheses.
What does the rate of an S N 1 reaction depend on?
Only on the alkyl halide concentration, independent of the nucleophile concentration.
What role does alkyl halide chemistry play in understanding biochemical reactions?
It acts as a relatively simple model for more complex reactions in biomolecules.
What is the product of converting 1-methylcyclohexanol?
1-chloro-1-methylcyclohexane.
What is a common outcome of allylic bromination of an unsymmetrical alkene?
It often leads to a mixture of products.
What is Halomon and where is it isolated from?
A pentahalogenated alkene isolated from the red alga Portieria hornemannii.
What are S N 1 and S N 2 reactions known for in biological chemistry?
They are types of nucleophilic substitution reactions.
What are the pathways for the biosynthesis of?
The many thousands of terpenes.
What happens when HX reacts with a tertiary alcohol?
The reaction is so rapid that it can be carried out by bubbling pure HCl or HBr gas into a cold ether solution of the alcohol.
What is a key characteristic of the carbocation involved in S N 1 reactions?
It is typically a 1° (primary) carbocation.
What is the significance of other halo-substituted compounds?
They provide important leads to new medicines.
How does charge stabilization by the leaving group affect the transition state?
The greater the stabilization, the lower the energy of the transition state and the more rapid the reaction.
What is the E1cB reaction characterized by?
The formation of a conjugate base as an intermediate.
What type of elimination occurs with primary alkyl halides when a strong base is used?
E2 elimination.
What are alkyl halides also known as?
Haloalkanes.
What type of acid is involved in the E1cB reaction?
A -acid.
What is the charge distribution in the carbon-halogen bond of alkyl halides?
The carbon atom bears a slight positive charge (δ+) and the halogen a slight negative charge (δ-).
What are the different mechanisms by which elimination reactions can occur?
E1, E2, and E1cB reactions.
What is the charge of the product if the nucleophile is neutral?
The product is positively charged.
How stable are primary allylic and primary benzylic carbocations compared to secondary alkyl carbocations?
They are about as stable as secondary alkyl carbocations.
What is the significance of resonance stabilization in carbocations?
It increases the stability of primary allylic and benzylic carbocations.
How are simple alkyl halides typically named?
By identifying the alkyl group first and then the halogen.
What type of bases make good leaving groups?
Weak bases such as Cl⁻ and tosylate ion.
What types of reactions do alkyl halides undergo?
Nucleophilic substitutions and eliminations.
What type of kinetics do E2 reactions exhibit?
Second-order kinetics.
In which type of solvents do S N 1 reactions occur more rapidly?
In polar solvents such as water and methanol.
Why are allylic radicals considered stable?
Because they are stabilized by resonance.
What role do protic solvents play in S N 1 reactions?
They can help the leaving group to leave.
How do S N 2 reactions differ from S N 1 reactions in terms of conditions?
S N 2 reactions occur under basic conditions, making the nucleophile stronger.
What type of arrow should be used in allylic bromination mechanisms?
A single arrow (單箭頭).
What is a characteristic of the S N 1 reaction?
It involves nearly second-ordered substrates.
What does S N 1 stand for?
Unimolecular nucleophilic substitution reaction.
Can allylic and benzylic substrates undergo both S N 2 and S N 1 reactions?
Yes, they can undergo both types of reactions.
What is the structure represented by H3C–C–CH2–OH?
It is an alcohol with a hydroxyl group (-OH) attached to a carbon chain.
What are some industrial applications of alkyl halides?
Inhaled anesthetics, refrigerants, pesticides, and solvents.
What is the general formula for Grignard Reagents?
RMgX, where R is an alkyl group and X is a halide.
What type of carbocation intermediates does the S N 1 reaction favor?
More highly stabilized carbocation intermediates.
How are alkyl halides used in dry-cleaning?
As solvents.
What is the main focus of Worked Example 12.4?
Predicting the product of an elimination reaction.
What type of alkene is typically used in allylic bromination?
Unsymmetrical alkene.
What role does the leaving group play in the S N 1 reaction?
It shields one side of the carbocation intermediate and forms an ion-pair.
What is the role of the nucleophile in the S N 1 reaction?
It does not affect the S N 1 reaction rate.
What is the biological equivalent of a halogen?
The diphosphate group.
What are haloalkanes commonly called?
Alkyl halides.
What type of electrons act as nucleophiles in biological substitution reactions?
π electrons.
Where do S N 2 reactions occur?
Only at relatively unhindered sites.
What influences the speed of an S N 1 reaction?
The stability of the carbocation intermediate.
What type of nucleophile is favored in basic conditions?
Strong nucleophile.
What types of charges can a nucleophile have?
It can be either neutral or negatively charged.
How does steric hindrance affect nucleophilicity?
Less hindered nucleophiles are more reactive than much hindered ones.
What is the relationship between ∆ G ‡ and the rate of S N 2 reactions?
A decrease in ∆ G ‡ increases the S N 2 reaction rate.
What effect does steric hindrance have on the S N 2 transition state?
It raises the energy of the transition state, increasing ∆G ‡ and decreasing the reaction rate.
What is the relationship between nucleophile strength and basic conditions?
In basic conditions, strong nucleophiles are more effective.
What type of reaction is characterized by steric effects?
The S N 2 reaction.
Which elimination mechanism predominates in biological pathways?
E1cB.
What is a key characteristic of the S N 2 reaction regarding the leaving group?
The leaving group is crucial for the reaction's success.
What type of reaction occurs when 1-chloro-1-methylcyclohexane reacts with KOH in ethanol?
An elimination reaction.
What does an elimination reaction involve when a nucleophile reacts with an alkyl halide?
The elimination of HX by reacting at a neighboring hydrogen.
What rule is associated with elimination reactions?
Zaitsev’s Rule.
What is the rate-limiting step in an S N 1 reaction?
The spontaneous dissociation of the alkyl halide to give a carbocation intermediate.
What type of alcohol is found in roses and used in perfumery?
A fragrant alcohol.
What does Zaitsev's rule state regarding elimination reactions?
In the elimination of HX from an alkyl halide, the more highly substituted alkene product predominates.
Which ion is more basic and more nucleophilic than acetate ion (CH3CO2-)?
OH- (hydroxide ion).
What are the two types of periplanar arrangements in E2 reactions?
Anti periplanar and syn periplanar.
What type of carbon atom is bonded to a halogen in alkyl halides?
A saturated sp3-hybridized carbon atom.
What is a nucleophile?
A Lewis base in inorganic chemistry that has an unshared pair of electrons.
What is the precursor of epinephrine?
Norepinephrine.
What does the Hammond postulate state?
Any factor that stabilizes a high-energy intermediate also stabilizes the transition state leading to that intermediate.
What type of reaction shows an identical reactivity order for leaving groups?
Both S N 1 and S N 2 reactions.
What types of reactions can occur when a nucleophile reacts with an alkyl halide?
Substitution and elimination.
What is the purpose of Worked Example 12.1?
To illustrate a specific concept or problem-solving method.
What are the reactions of HX and X2 with alkenes classified as?
Electrophilic addition reactions.
What type of alkyl halide or tosylate undergoes nucleophilic substitution with inversion of configuration?
Primary or secondary alkyl halide or tosylate.
How do protic solvents affect S N 2 reactions?
They generally slow down S N 2 reactions.
What is the second solution in the sequence?
2
What type of substitution occurs with primary alkyl halides when a good nucleophile is used?
S N 2 substitution.
What happens during the substitution reaction of alkyl halides?
The X group is replaced by the nucleophile.
Which solvents slow down S N 1 reactions?
Nonpolar solvents such as ether and chloroform.
What is the rate-limiting step in a chemical reaction?
The slowest step of a multi-step chemical reaction.
How does acetate ion (CH3CO2-) compare to water (H2O) in terms of basicity and nucleophilicity?
Acetate ion is more basic and more nucleophilic than water.
What is the product of the E2 reaction with HBr?
(Z)-1-bromo-1,2-diphenylethylene.
What type of base is typically used in an E2 reaction?
A strong base, such as hydroxide ion or alkoxide ion (RO-).
What type of nucleophiles are usually more reactive in S N 2 reactions?
Negatively charged nucleophiles.
How does the E2 reaction occur?
In a single step through a transition state where the double bond forms as H and X groups leave.
为什么在反应中会出现反转产物？
因为反应是一步骤两箭头的机制，导致反加成。
What type of reaction is S N 2?
A nucleophilic substitution reaction.
What is the focus of the topic 'Naming Alkyl Halides'?
It involves the systematic naming of alkyl halides based on their structure.
What does the structure H3C CH3 CH2–O represent?
It is an ether with an alkoxy group (-O) attached to a carbon chain.
Which method is considered the simplest for converting alcohols to alkyl halides?
Treating the alcohol with HCl, HBr, or HI.
Which hydrogen halides react with alkenes to produce Markovnikov addition products?
HCl, HBr, and HI.
What is the stereochemical outcome of nucleophilic substitution reactions of primary or secondary alkyl halides?
Inversion of configuration.
In which type of biological pathways do elimination reactions occur?
Various biological pathways.
What is the impact of good leaving groups on the rate of S N 2 reactions?
They increase the S N 2 reaction rate.
Which types of alcohols are best converted into alkyl halides using SOCl2 or PBr3?
Primary and secondary alcohols.
What type of nucleophile stabilizes the transition state in S N 2 reactions?
Soft nucleophiles (Nu) or leaving groups (X).
What type of bases make poor leaving groups?
Strong bases such as OH⁻ and NH₂⁻.
What happens if X is a good leaving group in the context of E1cB?
E1 and E2 reactions might occur.
Under what condition does E1cB elimination occur?
When the leaving group is two carbons away from a carbonyl group.
How is the halogen treated in the naming of alkyl halides?
As a substituent on a parent alkane chain.
What is the most commonly occurring pathway for elimination in the laboratory?
E2 Reaction.
What is significant about the oxygen in TosO?
There is a change in the color of oxygen, indicating resonance.
What is the Deuterium isotope effect?
It refers to the observation that a C-H bond is more easily broken than an equivalent C-D bond.
在酸性条件下，弱亲核试剂的反应机制是什么？
是 S N 2 的混合体，因为有反转产物和反加成。
How much more stable are allylic radicals compared to vinylic radicals?
About 85 kJ/mol (19 kcal/mol).
What is the charge of the product if the nucleophile is negatively charged?
The product is neutral.
What must happen to the sp3 orbitals in the reactant C-H and C-X bonds during the E2 reaction?
They must overlap and become p orbitals in the alkene product.
In a substitution reaction, what does the nucleophile substitute for?
The halide.
What is Zaitsev's Rule?
Zaitsev's Rule states that in elimination reactions, the more substituted alkene is the major product.
What is the first solution in the sequence?
1
What is the role of NBS in the reaction with 4,4-dimethylcyclohexene?
NBS acts as a brominating agent.
What type of bond is formed in allylic bromination?
σ bond = sp2 + s.
What does Zaitsev's Rule predict about alkene formation?
It predicts that the more stable, more substituted alkene will be favored in elimination reactions.
In what type of solvent do E1 and S N 1 reactions typically occur?
In a protic solvent.
What does S N 2 stand for?
Substitution Nucleophilic Bimolecular.
What happens to the reaction rate if the concentration of OH- doubles?
The reaction rate also doubles.
In the E1 reaction, which bond breaks first?
The C-X bond breaks before the C-H bond.
What characterizes the S N 2 reaction?
It involves a single concerted step with a backside attack by the nucleophile.
What type of cations are stabilized by resonance in the context of S N 1 reactions?
Allylic and benzylic cations.
What effect does resonance have on allylic and benzylic cations in S N 1 reactions?
It stabilizes the cations, favoring the reaction.
What characterizes the best leaving groups in a reaction?
They stabilize the negative charge in the transition state.
What is the rate law for E2 reactions?
Rate = k [RX][Base].
What are the characteristics of the S N 1 reaction?
The reaction rate is independent of the nucleophile.
What type of reactions are discussed in the context of biological chemistry?
Biological substitution reactions.
What is the process of forming alkyl halides from alkenes called?
Allylic bromination.
How do halogens change in size down the periodic table?
They increase in size.
What is a key characteristic of S N 2 reactions?
They require relatively unhindered substrates for reactivity.
What stereochemical configuration is formed in the E2 reaction described?
Z-form.
What does isotope-labeled refer to in nucleophilic substitution reactions?
The use of isotopes to track the reaction mechanism.
What trend is observed in carbon-halogen bond strengths as you move down the periodic table?
The C-X bond strengths decrease.
What types of reactions occur together under neutral conditions for tertiary alkyl halides?
S N 1 substitution and E1 elimination.
What type of reaction occurs when 4,4-dimethylcyclohexene reacts with NBS?
Allylic bromination.
What are nucleophilic substitution reactions?
One of the most common and versatile reaction types in organic chemistry.
What are the three types of elimination reactions mentioned?
E1, E1cB, and E2.
What type of problem is typically addressed in Worked Examples?
Practical applications of theoretical concepts.
What is the key characteristic of the S N 1 reaction mechanism?
It involves a two-step process where the rate-determining step is the formation of a carbocation.
What is the stereochemistry of the reactant (R)-1-bromo-1-phenylethane?
It has an R configuration.
What postulate explains the relationship between carbocation stability and S N 1 reaction rate?
Hammond postulate.
Why are epoxides more reactive than other ethers?
Due to angle strain in the three-membered ring.
What role does the Br• radical play in the allylic bromination mechanism?
It cycles back to carry on the chain reaction.
What happens to the nucleophile in protic solvents during S N 2 reactions?
Solvent molecules hydrogen bond to the nucleophile, forming 'a cage' around it.
What reaction is likely to predominate when a secondary, non-allylic substrate is treated with a strong base?
E2 reaction.
How do primary and secondary alcohols react in the transformation to alkyl halides?
They react slowly and at higher reaction temperatures.
What is retention in the context of chemistry?
Retention refers to the ability of a substance to remain in a particular phase or medium during a separation process.
What was the focus of investigations in the 1920s and 1930s regarding nucleophilic substitution reactions?
To clarify the mechanism of nucleophilic substitution reactions and understand how inversions of configuration occur.
What do Grignard Reagents react with?
Weak acids such as H2O, ROH, RCO2H, and RNH2.
What type of nucleophile is preferred in acidic conditions?
Weak nucleophile.
What is a characteristic of S N 1 reactions under acidic conditions?
Neutral water can sometimes be the leaving group.
What type of addition occurs under acidic conditions?
Anti-addition.
What is the equation for the rate of an S N 1 reaction?
Rate = Rate of disappearance of alkyl halide = RX × k.
What must be done to a primary or secondary alcohol to carry out an S N 2 reaction?
The HO– must be converted into a better leaving group by reaction with SOCl2 or PBr3.
What is a key characteristic of the leaving group in nucleophilic substitution reactions?
An identical reactivity order is found for the S N 1 reaction as for the S N 2 reaction.
How does the ground-state energy of good nucleophiles affect the reaction rate?
Good nucleophiles have high ground-state energy, which decreases ∆ G ‡ and increases the S N 2 reaction rate.
What is a protic solvent?
A solvent that has hydrogen atoms bonded to electronegative atoms, allowing it to donate protons (H+).
How does the rate of C-H bond cleavage compare to C-D bond cleavage?
The rate of C-H bond cleavage is faster than that of C-D bond cleavage.
What is the effect of good leaving groups on the transition state in S N 2 reactions?
Good leaving groups lower the energy of the transition state.
What are the best reagents for converting primary and secondary alcohols into alkyl halides?
Thionyl chloride (SOCl2) or phosphorus tribromide (PBr3).
What type of stereochemical change occurs during the nucleophilic substitution reaction of (R)-1-bromo-1-phenylethane?
Inversion of configuration occurs.
Under what condition can an E2 reaction occur in cyclohexane?
When the hydrogen and the leaving group are trans diaxial.
What is essential for the overlap of orbitals in the transition state of an E2 reaction?
All orbitals must be periplanar.
What type of reaction is characterized by a single concerted step?
S N 2 reaction.
What is the stability comparison between negatively charged nucleophiles and neutral nucleophiles?
Negatively charged nucleophiles are less stable and have a higher ground-state energy than neutral ones.
What type of reaction is the E1 reaction?
A unimolecular elimination reaction.
What do polar solvents solvate in a reaction?
Metal cations rather than nucleophilic anions.
What type of bond is formed in the context of alkyl radicals?
σ bond = sp3 + s.
How do protic solvents affect nucleophiles in S N 2 reactions?
Protic solvents solvate the nucleophile, lowering its ground-state energy, increasing ∆G ‡, and decreasing the S N 2 reaction rate.
What type of substrates yield the most stable carbocations in S N 1 reactions?
Tertiary, secondary, allylic, and benzylic halides.
What type of intermediate is formed in an S N 1 reaction with a chiral reactant?
An achiral carbocation intermediate.
When does the rupture of the C-H (or C-D) bond occur in E1 reactions?
After the rate-limiting step rather than during it.
What is required for a successful backside displacement in S N 2 reactions?
The nucleophile must approach the carbon atom from the opposite side of the leaving group.
What is Zaitsev's Rule?
A principle that states that the more substituted alkene will be the major product in elimination reactions.
In what solvent is the reaction of 1-chloro-1-methylcyclohexane with KOH conducted?
In ethanol.
What is the rate-determining step in an S N 1 reaction?
The formation of the carbocation.
What type of reaction is the E1cB reaction?
A unimolecular elimination reaction.
Which compounds do not typically undergo S N 2 reactions?
Alkyl fluorides, alcohols, ethers, and amines.
What type of elimination occurs in the E2 reaction of HBr?
Anti periplanar elimination.
What determines the rate of a chemical reaction?
∆G‡, the energy difference between the reactant ground state and the transition state.
Where are alkyl halides commonly found?
Widespread in nature.
How much more stable are allylic radicals compared to related alkyl radicals?
About 40 kJ/mol (9 kcal/mol).
What must be included in the parent chain if present?
A double or triple bond.
Who discovered Grignard Reagents?
Victor Grignard.
Where do all three elimination mechanisms occur?
In the laboratory.
Under what conditions are S N 2 reactions often carried out?
Basic conditions.
What factor increases the rate of an S N 1 reaction?
Any factor stabilizing the intermediate carbocation.
What follows the dissociation in an E1 reaction?
Loss of H+ from the adjacent carbon.
How does nucleophilicity relate to basicity in S N 2 reactions?
Nucleophilicity roughly parallels basicity when comparing nucleophiles with the same reacting atom.
What type of conditions are required for the conversion of alcohols to alkyl halides?
Mild conditions.
What does kinetics study?
The relationship between the reaction rate and the concentrations of the reactants.
When does E1cB elimination take place?
If the leaving group is two carbons away from a carbonyl group.
What type of addition do bromine and chlorine undergo with alkenes?
Anti addition through a halonium ion intermediate.
What do Grignard reagents model?
More complex carbon-based nucleophiles important in biological chemistry.
What is the typical excess of inversion in S N 1 reactions?
0-20%.
What are Grignard Reagents?
Magnesium salts of carbon acids, represented as R3C-MgX.
What ion is substituted by acetate in the nucleophilic substitution reaction?
Tosylate ion.
At what temperature is 2-chloro-2-methylpropane warmed during the reaction?
65ºC.
What intermediate is formed during the E1 reaction?
A carbocation intermediate.
What is basicity?
The affinity of a base for a proton (H+).
How can the product composition of an S N 1 reaction be expressed in terms of percentages?
40% R and 60% S.
What is the relationship between symmetrical and unsymmetrical epoxides in terms of product formation?
Unsymmetrical epoxides yield a minor product, while symmetrical ones yield a major product.
What factors can influence retention in chromatography?
Factors include the nature of the stationary phase, mobile phase, temperature, and the chemical properties of the analytes.
What is t-heptoxide?
A strong base similar to t-butoxide, used in elimination reactions.
What are the key characteristics of the S N 2 reaction?
Inversion of configuration and second-order kinetics.
What is the geometry of the transition state in an S N 2 reaction?
The transition state has a trigonal bipyramidal geometry, where the nucleophile, substrate, and leaving group are arranged around the central carbon atom.
What effect does raising the reactant energy have on the reaction rate?
It decreases ∆G‡ and increases the reaction rate.
What is TosO in the context of nucleophilic substitution reactions?
A good leaving group with resonance.
What characterizes good nucleophiles in terms of stability?
Good nucleophiles are less stable.
How does the carbon atom in alkyl halides behave in polar reactions?
It behaves as an electrophile.
What is the order of halide reactivity?
I- > Br- > Cl-.
What affects the reactivity of substrates in S N 2 reactions?
The steric hindrance of the site where the reaction occurs.
Rank the stability of carbocations from most to least stable.
3º > 2º > 1º > –CH3.
What are common methods to transform alcohols into alkyl halides?
Treat the alcohol with HCl, HBr, or HI.
What type of reaction is S N 1?
A unimolecular nucleophilic substitution reaction.
What is the role of Grignard reagents in biochemistry?
They have no role in biochemistry.
What is the stereochemical consequence of anti periplanar geometry in E2 eliminations?
It leads to the formation of specific alkene isomers.
Who discovered the nucleophilic substitution reaction?
Paul Walden, a German chemist.
What does the first-order kinetics in E1 reactions indicate?
It indicates a rate-limiting, unimolecular dissociation process.
What mechanism does the Deuterium isotope effect support?
The E2 mechanism.
What product is formed when meso-1,2-dibromo-1,2-diphenylethane undergoes E2 elimination?
Only the E alkene is formed.
How can worked examples benefit students?
They provide step-by-step guidance on solving problems.
What is N-bromosuccinimide (NBS) used for in organic chemistry?
It is used for bromination of alkenes to prepare alkyl halides.
What is Zaitsev’s Rule related to?
The preference for the more substituted alkene in elimination reactions.
What is a summary of the reactivity of tertiary alkyl halides?
S N 1, S N 2, E1, E1cB, and E2.
What type of orbitals do sp3 orbitals become in the alkene product of an E2 reaction?
They become sp2 orbitals.
How does carbocation solvation affect S N 1 reactions?
It stabilizes the carbocation intermediate, increasing the reaction rate.
What process allows the interconversion of enantiomers in Walden's discovery?
A series of simple substitution reactions.
What types of substances can be prepared using S N 2 reactions?
A wide array of organic compounds, including alkyl halides and ethers.
What is the sequence involved in the interconversion of enantiomers of 1-phenylpropan-2-ol?
A three-step sequence.
How does nucleophilicity change in the periodic table?
Nucleophilicity usually increases going down a column.
How is racemization calculated in S N 1 reactions?
Racemization = 40% + 40%.
What is the pKa range of hydrocarbons?
44 to 60.
How is the E1 reaction analogous to another type of reaction?
It is analogous to the S N 1 reaction.
What is the role of stereochemistry in determining the product of an E2 reaction?
The stereochemistry of the starting material influences the stereochemical outcome of the alkene product.
What happens after the carbanion is formed in the E1cB reaction?
The carbanion expels a leaving group on the adjacent carbon.
What effect do acidic conditions have on S N 1 reactions?
They make the substrate dissociate.
What is the mechanism associated with biological substitution reactions mentioned?
S N 1.
Which is more nucleophilic: HS- or HO-?
HS- is more nucleophilic than HO-.
What is involved in the S N 2 transition state?
Partial bond formation between the incoming nucleophile and the alkyl halide carbon atom.
What is the main difference between E1, E2, and E1cB reactions?
They differ in the timing of C-H and C-X bond breaking.
What type of reaction is involved in the biosynthesis of epinephrine?
Biological substitution reactions.
What happens to reactivity as you go down the periodic table?
Elements have their valence electrons in successively larger shells, farther from the nucleus, less tightly held, and consequently more reactive.
What initiates the E1 elimination reaction?
A unimolecular dissociation similar to the S N 1 reaction.
What is the role of light in the preparation of alkyl halides from alkenes?
It facilitates the reaction with N-bromosuccinimide (NBS).
What does the Hammond postulate suggest about allylic radicals?
Allylic radicals should form faster.
What is required for E2 elimination to occur?
A strong base.
What are the characteristics of S N 2 reactions?
They involve a single concerted step and result in inversion of configuration.
What type of solvent is used in the reaction of 2-chloro-2-methylpropane?
Protic solvent.
What does Zaitsev's Rule imply about alkene stability?
It implies that more substituted alkenes are generally more stable due to hyperconjugation and inductive effects.
What type of reaction can a secondary, non-allylic substrate undergo with a good nucleophile in a polar aprotic solvent?
S N 2 reaction.
What to do if the parent chain can be numbered from either end?
Begin at the end nearer the substituent that has alphabetical precedence.
What is the stereochemistry of the product (S)-1-cyano-1-phenylethane?
It has an S configuration.
In which type of reactions is Zaitsev's Rule commonly applied?
In elimination reactions, specifically E1 and E2 mechanisms.
What compounds did Paul Walden study in his discovery?
Pure enantiomers (+) and (-)-Malic acids.
What is nucleophilicity?
The affinity of a Lewis base for a carbon atom (C(δ+)) in the S N 2 reaction.
Can Grignard Reagents be made from other types of halides?
Yes, they can also be made from alkenyl (vinylic) and aryl (aromatic) halides.
What is the effect of using a protic solvent on a secondary benzylic substrate?
It favors E2 reaction when treated with a base.
With what do epoxides react readily?
Many other nucleophiles.
What reaction is used to convert allylic bromination products into conjugated dienes?
Dehydrohalogenation with base.
What is the fifth solution in the sequence?
2
What type of reaction is characterized by a single transition state and a concerted mechanism?
S N 2 reaction.
What type of elimination reaction is favored with a secondary alkyl halide and a strong base?
E2, producing an alkene.
What type of substrates favor S N 2 reactions?
Primary and some secondary substrates are favored due to less steric hindrance.
What is a characteristic of a strong base?
It completely dissociates in solution and has a high pH.
Who suggested the S N 2 mechanism?
E. D. Hughes and Christopher Ingold in 1937.
What types of substrates are particularly reactive in S N 2 and S N 1 reactions?
Allylic and benzylic substrates.
What is the first step in naming alkyl halides?
Find the longest chain and name it as the parent.
What happens to the lengths of carbon-halogen bonds as you move down the periodic table?
They increase accordingly.
What is chloromethane released by?
Ocean kelp, forest fires, and volcanoes.
What are the stereochemical descriptors for the product of the E2 reaction?
1S,2S.
What is the significance of anti periplanar geometry in cyclohexane rings?
It creates a rigid relationship between substituents on adjacent carbon atoms.
What is an aprotic solvent?
A solvent that does not have hydrogen atoms bonded to electronegative atoms, and cannot donate protons.
What type of reaction occurs when 2-chloro-2-methylpropane is warmed to 65ºC in 80% aqueous ethanol?
E1 and S N 1 reactions.
What is Zaitsev's Rule?
Zaitsev's Rule states that in elimination reactions, the more substituted alkene is the major product.
For which types of substrates are S N 2 reactions best suited?
Methyl and primary substrates.
What should you do after numbering the carbons of the parent chain?
Assign each substituent a number according to its position on the chain.
How are Grignard Reagents produced?
From the reaction of alkyl halides (RX) with magnesium metal in ether or THF.
What reaction occurs when a secondary benzylic substrate is treated with a base?
E2 reaction.
弱亲核试剂的行为类似于哪种反应机制？
类似于 S N 1 反应机制。
What happens to the optical activity of the product in an S N 1 reaction involving a chiral reactant?
The product will be optically inactive.
What is the electron configuration of the sp3 orbitals in the reactant during the E2 reaction?
2 electrons in sp3 and no electrons in sp3.
What type of solvent is preferred for S N 1 reactions?
Polar solvent.
What is a common feature of worked examples in textbooks?
They often include both the solution and explanations.
What mechanism is involved in the conversion of alcohols to alkyl halides?
S N 2 mechanism.
What is the effect of polar aprotic solvents on nucleophiles in S N 2 reactions?
Polar aprotic solvents surround the cation but not the nucleophilic anion, raising the ground-state energy of the nucleophile, decreasing ∆G ‡, and increasing the S N 2 reaction rate.
What type of compounds are frequently converted to conjugated unsaturated carbonyl compounds?
3-hydroxy carbonyl compounds.
What is the significance of the discovery of the nucleophilic substitution reaction?
It highlights the mechanism and stereochemical outcomes of reactions involving alkyl halides and tosylates.
What type of reaction is likely to occur with a primary alkyl halide in a polar aprotic solvent?
S N 2, resulting in an inversion of configuration.
What type of products are usually obtained from E1 reactions?
Mixtures of substitution and elimination products.
What type of stereochemistry is observed in S N 2 reactions?
Inversion of configuration at the carbon center.
Which step is rate-limiting in the E1 reaction?
The first step.
What is a key feature of the S N 2 reaction mechanism?
It involves a backside attack by the nucleophile.
What is the stereochemical outcome of an S N 2 reaction?
Inversion of configuration at the carbon center.
What is the significance of retention in the context of reaction mechanisms?
Retention can indicate the stability of intermediates and the likelihood of certain pathways in reaction mechanisms.
What is the relationship between transition state energy and reaction rate?
Decreasing transition state energy decreases ∆G‡ and increases the reaction rate.
Why does bromomethane result in a fast S N 2 reaction?
Because it is readily accessible.
What role does norepinephrine play in the synthesis of epinephrine?
It acts as a precursor.
What type of kinetics do E1 reactions exhibit?
First-order kinetics.
What would happen if an E1 reaction occurs regarding C-H and C-D bonds?
There would be no difference in the cleavage rates between C-H and C-D bonds.
How do good leaving groups affect the activation energy (∆ G ‡) in S N 2 reactions?
They decrease ∆ G ‡.
Why is a polar solvent required in chemical reactions?
Because polar solvents can dissolve many salts due to their high polarity.
What position does bromine substitute for hydrogen in allylic bromination?
At the allylic position, which is next to the double bond.
What is the effect of methanol and ethanol on S N 2 reactions?
They slow down S N 2 reactions by solvation of the reactant nucleophile.
What happens to the reaction rate of S N 2 reactions with increased steric hindrance?
The reaction rate decreases.
What products can be expected from the allylic bromination of 4,4-dimethylcyclohexene?
Brominated products at the allylic positions.
What is the expected product from the elimination reaction of 1-chloro-1-methylcyclohexane with KOH?
1-methylcyclohexene.
Why are vinylic halides and aryl halides unreactive in S N 2 reactions?
The incoming nucleophile must approach in the plane of the carbon-carbon double bond, which is electron-rich, making backside displacement difficult.
What is a characteristic of the S N 2 reaction?
It involves a direct nucleophilic attack on the substrate, leading to a simultaneous bond formation and bond breaking.
What can products of allylic bromination reactions be converted into?
Conjugated dienes by dehydrohalogenation with base.
What type of reaction is likely to occur with a tertiary alkyl halide in a polar protic solvent?
S N 1, leading to a racemic mixture of products.
How do good leaving groups affect the reaction rate in S N 1 reactions?
They increase the reaction rate by lowering the energy level of the transition state for carbocation formation.
How does the rate of an S N 2 reaction depend on the reactants?
The rate depends on the concentration of both the nucleophile and the substrate.
What reaction predominates when a strong base is used with secondary alkyl halides?
E2 elimination.
What is the result of Grignard Reagents reacting with weak acids?
They abstract a proton and yield hydrocarbons.
What factors influence the rate of a simple nucleophilic substitution reaction?
Temperature and concentration of reactants.
What type of mechanism does S N 1 follow?
A two-step mechanism.
What is the relationship between retention time and polarity?
Generally, more polar compounds have longer retention times on polar stationary phases.
What intermediate is formed in the E1cB reaction?
A carbanion intermediate, usually a conjugate base.
What is the difference between E2 and E1 mechanisms?
E2 is a one-step mechanism, while E1 involves a two-step process.
What type of solvent is an aprotic solvent?
A solvent that cannot donate protons (H+).
What is the effect of solvent on S N 2 reactions?
Polar aprotic solvents generally favor S N 2 reactions by stabilizing the nucleophile.
How can alkyl halides be prepared from alkenes?
By reaction with N-bromosuccinimide (NBS) in the presence of light.
What is the expected product from the nucleophilic substitution reaction of (R)-1-bromo-1-phenylethane with cyanide ion?
The product is (S)-1-cyano-1-phenylethane.
What are protic solvents?
Solvents that contain an -OH or -NH group.
How should you number the carbons of the parent chain in alkyl halide nomenclature?
Begin at the end nearer the first substituent, whether alkyl or halo.
What is the first step in the mechanism of allylic bromination?
A Br• radical abstracts an allylic hydrogen atom of the alkene, forming an allylic radical plus HBr.
What type of reaction can a secondary benzylic substrate undergo with a nonbasic nucleophile in a polar aprotic solvent?
S N 2 reaction.
弱亲核试剂在反应中可以攻击哪个碳？
带有较多正电荷的高级碳。
How do protic solvents affect nucleophilic substitution reactions?
They stabilize cations and can participate in hydrogen bonding, influencing reaction rates.
What functional group is present in H3C–C–CH2–OH?
Hydroxyl group (-OH).
What year was the nucleophilic substitution reaction discovered?
What is the rate of an S N 1 reaction dependent on?
The concentration of the substrate only, not the nucleophile.
What type of compounds are Grignard Reagents?
Organometallic compounds, as they contain a carbon-metal bond.
What functional group is present in H3C CH3 CH2–O?
Ether group (-O).
What do epoxides react with in aqueous acid?
They give 1,2-diols.
What is the significance of the unsymmetrical nature of 4,4-dimethylcyclohexene in the reaction with NBS?
It leads to the formation of multiple bromination products due to different possible allylic positions.
What is the composition of the product in S N 1 reactions?
Approximately 80% racemized and 20% inverted.
What does S N 2 stand for in organic chemistry?
Nucleophilic Substitution, Second Order.
What is the purpose of forming a tosylate from an alcohol?
To increase its reactivity in nucleophilic substitution reactions.
What happens to the ground-state energy of the nucleophile in protic solvents?
It decreases, which increases ∆G ‡ and decreases the S N 2 reaction rate.
What is the role of t-butoxide in elimination reactions?
It is a strong base that can promote elimination reactions, often leading to less substituted alkenes when kinetic factors are considered.
What is the significance of stereochemistry in E2 reactions?
Stereochemistry affects the orientation of the double bond formed during the elimination process.
What type of solvent is a protic solvent?
A solvent that can donate protons (H+).
What type of reaction mechanism is involved in the conversion of allylic bromination products?
E2 mechanism.
What is a key characteristic of the substrate in S N 1 reactions?
It is typically tertiary or stabilized by resonance.
What is a stable carbocation intermediate?
A positively charged carbon species that is relatively stable due to its structure.
What is the abbreviation for Dimethylformamide?
DMF.
What does it indicate if ΔG > 0 in a reaction?
The reaction is non-spontaneous and requires energy input.
Which compound is a weaker nucleophile: DMSO or DMF?
DMF.
What is an electrophilic donor in the context of epinephrine biosynthesis?
A molecule that donates an electrophile during the reaction.
What is the outcome of S N 1 reactions on enantiomerically pure substrates?
They do not occur with complete racemization.
What is Walden's cycle?
A process that involves the substitution of one nucleophile by another.
What type of reaction is facilitated by anti periplanar geometry in cyclohexane?
E2 reaction.
Which type of alcohol reacts best in the transformation to alkyl halides?
Tertiary alcohols (R3COH).
Which nucleophiles are involved in Walden's cycle?
Chloride ion (Cl-) and hydroxide ion (HO-).
Is there a deuterium isotope effect in E1 reactions?
No, E1 reactions show no deuterium isotope effect.
Is the Z alkene formed during the E2 elimination of meso-1,2-dibromo-1,2-diphenylethane?
No, the Z alkene is not formed.
How can an alcohol be made more reactive toward nucleophilic substitution?
By treating it with p-toluenesulfonyl chloride to form a tosylate.
What role does KOH play in the reaction with 1-chloro-1-methylcyclohexane?
KOH acts as a strong base to facilitate elimination.
What type of substitution occurs with secondary alkyl halides when a weakly basic nucleophile is used in a polar aprotic solvent?
S N 2 substitution.
What is the relationship between E1 substrates and S N 1 substrates?
The best E1 substrates are also the best S N 1 substrates.
What type of reaction is being discussed in the context of kinetics?
Nucleophilic substitution reaction (S N 2).
What are the two types of stereochemical outcomes observed in nucleophilic substitution reactions?
Retention and inversion.
What is the expected product distribution from an S N 1 reaction involving a symmetrical intermediate?
A racemic 50:50 mixture of enantiomers.
Under what condition does E1cB elimination occur?
If the leaving group is two carbons away from a carbonyl group.
In the E1cB reaction, which bond breaks first?
The C-H bond breaks before the C-X bond.
How do kinetic concerns affect elimination reactions?
Kinetic factors can lead to the formation of less stable, less substituted alkenes, contrary to Zaitsev's Rule.
What does S N 1 stand for?
Substitution Nucleophilic Unimolecular.
How does the strength of the nucleophile affect the S N 2 reaction?
A stronger nucleophile increases the reaction rate.
Which mechanism is favored by strong nucleophiles and primary substrates?
S N 2 mechanism.
What characterizes a stable transition state?
It has a low energy level compared to other transition states.
What does the allylic radical react with in the allylic bromination mechanism?
It reacts with Br2 to yield the product and a Br• radical.
How are Grignard reagents useful in laboratory reactions?
They are useful carbon-based nucleophiles.
What are vinylic halides and aryl halides in relation to S N 2 reactions?
They are unreactive toward S N 2 reactions.
How do aprotic solvents influence nucleophilic substitution reactions?
They do not stabilize cations as effectively, often leading to faster reaction rates for nucleophiles.
What types of nucleophiles are typically involved in S N 2 reactions?
Soft and hard nucleophiles.
What type of solvent is required for a secondary benzylic substrate to undergo an S N 2 reaction?
Polar aprotic solvent.
What type of nucleophile is involved in E1 and S N 1 reactions?
A nonbasic nucleophile.
What is a key characteristic of the S N 2 reaction mechanism?
It involves a nucleophile attacking the substrate and displacing a leaving group simultaneously.
What is the effect of doubling the concentration of CH3Br on the reaction rate?
The reaction rate doubles.
What type of solvent is preferred for S N 2 reactions with secondary substrates?
Polar aprotic solvent.
What is the role of the halonium ion in the addition of bromine and chlorine to alkenes?
It acts as an intermediate in the anti addition process.
Is there a geometric requirement for E1 reactions?
No, there is no geometric requirement on the E1 reaction.
What type of reaction is the S N 2 reaction?
Second-order reaction.
What does S N 2 stand for?
Substitution, nucleophilic, bimolecular.
What is the sixth solution in the sequence?
3
What type of elimination mechanism is involved in the reaction of (1S,2S)-1,2-dibromo-1,2-diphenylethane?
E2 elimination mechanism.
Why are carbon anions considered very strong bases?
Because hydrocarbons are weak acids with high pKa values.
What is Dimethyl sulfoxide commonly abbreviated as?
DMSO.
What is the rate-determining step in an S N 1 reaction?
The formation of the carbocation.
What does HMPA stand for?
Hexamethylphosphoramide.
What role does the solvent play in S N 1 reactions?
Polar protic solvents stabilize the carbocation and the leaving group.
In which step does the inversion of stereochemical configuration occur during nucleophilic substitution?
In the second step.
How do negatively charged nucleophiles affect the activation energy (∆G‡) in S N 2 reactions?
They decrease ∆G‡, leading to an increased S N 2 reaction rate.
In the context of Zaitsev's Rule, what is meant by 'more substituted'?
More substituted refers to alkenes that have more alkyl groups attached to the double bond.
What type of products do bromine and chlorine yield when added to alkenes?
1,2-dihalogenated products.
What is the difference between soft and hard nucleophiles in S N 2 reactions?
Soft nucleophiles are more polarizable and less electronegative, while hard nucleophiles are less polarizable and more electronegative.
What is the effect of nucleophile charge on the S N 2 reaction rate?
Basic, negatively charged nucleophiles increase the S N 2 reaction rate.
What is the fourth solution in the sequence?
1
What stereochemistry is expected for the alkene obtained by E2 elimination of (1S,2S)-1,2-dibromo-1,2-diphenylethane?
The alkene will have a trans stereochemistry.
What is one example of a biological process involving elimination reactions?
Biosynthesis of fats.
What is the primary mechanism of the S N 2 reaction?
It involves a single concerted step where the nucleophile attacks the substrate and the leaving group departs simultaneously.
How are the halide and hydrogen lost in E1 reactions?
They are lost in separate steps.
How does the transition state affect the rate of an S N 2 reaction?
The rate of an S N 2 reaction depends on the concentration of both the nucleophile and the substrate, as the transition state involves a simultaneous bond formation and bond breaking.
What reactions occur when a weakly basic nucleophile is used in a protic solvent?
S N 1 and E1 reactions.
What is an example of a nucleophile mentioned?
CN⁻.
What factors affect the rate of an S N 2 reaction?
Nucleophile strength, substrate structure, and leaving group ability.
What role does the leaving group play in an S N 2 reaction?
A better leaving group enhances the reaction rate.
What is formed during the S N 2 reaction?
A transition state.
Is a strong base used in the reaction of 2-chloro-2-methylpropane?
No, a strong base is not used.
Which elimination mechanism is particularly common?
E1cB mechanism.
What is the third solution in the sequence?
3
How is Br2 generated in the allylic bromination process?
Br2 results from the reaction of NBS with the HBr formed in the first step.
What is the significance of Zaitsev's Rule in organic synthesis?
It helps predict the major product of elimination reactions, guiding synthetic strategies.
How does Zaitsev's Rule relate to the stability of alkenes?
More substituted alkenes are generally more stable due to hyperconjugation and inductive effects.
How does the symmetrical intermediate carbocation react with nucleophiles in an S N 1 reaction?
It can react equally well from either side.
What is the effect of a non-polar solvent on S N 1 reactions?
It is less effective as it does not stabilize the carbocation.
Does the nucleophile affect the reaction rate in S N 1 reactions?
No, the nucleophile does not affect the reaction rate.
What is the significance of allylic bromination in organic synthesis?
It allows for the preparation of alkyl halides from alkenes.
What role do polar solvents play in S N 1 reactions?
They stabilize the carbocation intermediate by solvation, thereby increasing the reaction rate.
In which type of mechanism does the nucleophile attack the substrate in a single step?
S N 2 mechanism.
What is the stereochemical outcome of an S N 2 reaction?
It results in inversion of configuration at the carbon center being attacked.
What is the significance of Et3CO in elimination reactions?
It is a strong base that can influence the outcome of elimination reactions, particularly in kinetic scenarios.
What does the Hammond postulate state regarding transition states?
The structure of a transition state resembles the structure of the nearest stable species.
Why do poor leaving groups disfavor alternative E1 and E2 reactions?
Because they do not facilitate the elimination process effectively.
What is a weak base?
A base that does not completely dissociate in solution and has a lower pH.
What is the significance of nucleophilic substitution reactions?
They are fundamental transformations in organic chemistry.
What does S N 1 stand for?
Substitution Nucleophilic Unimolecular.
What type of reaction is described in the context of meso-1,2-dibromo-1,2-diphenylethane?
E2 elimination reaction.
How does retention affect the outcome of chromatographic techniques?
Retention influences the separation efficiency and resolution of different components in a mixture.
How many steps are involved in the E1 reaction?
Two steps.
What is the mechanism of the S N 2 reaction?
A single concerted step where the nucleophile attacks the substrate and displaces the leaving group.
What happens to the ground-state energy of the nucleophile in polar aprotic solvents?
It increases, which decreases ∆G ‡ and increases the S N 2 reaction rate.
What type of substrates favor S N 2 reactions?
Primary and some secondary substrates.
How is inversion calculated in S N 1 reactions?
Inversion = 100% - Racemization.
How is the rate of an S N 2 reaction mathematically expressed?
Reaction rate = k x [CH3Br] x [OH-].
What role does the leaving group play in the transition state of an S N 2 reaction?
The leaving group is partially bonded to the substrate in the transition state, facilitating its departure as the nucleophile forms a new bond.
What type of substrates commonly undergo the E1cB reaction?
Substrates with a poor leaving group, such as –OH, that is two carbons removed from a carbonyl group.
What is the effect of the substrate structure on S N 1 reactions?
Tertiary substrates react faster than secondary and primary substrates.
What is a common characteristic of the products of S N 1 reactions?
They can lead to racemization due to the planar nature of the carbocation.
What initiates the allylic bromination reaction?
The reaction is initiated by light (hν).
What is the relationship between strong bases and E2 reactions in secondary substrates?
Strong bases favor E2 reactions.
What is the transition state in an S N 2 reaction?
The transition state is a high-energy, unstable arrangement of atoms that occurs during the reaction as the nucleophile attacks the substrate and the leaving group departs.
What factors determine whether a nucleophilic substitution reaction is likely to be S N 1 or S N 2?
The structure of the substrate, the strength of the nucleophile, and the solvent used.
What is the relationship between the reaction rate and the concentrations of two species in an S N 2 reaction?
The reaction rate is linearly dependent on the concentrations of both species.
What type of reaction is likely to occur with a weak base and a tertiary alkyl halide?
E1, resulting in the formation of an alkene.
What effect does steric hindrance have on S N 2 reactions?
Increased steric hindrance decreases the rate of the reaction.
What visual representation is used to indicate bonds broken in nucleophilic substitution reactions?
Red wavy lines.
What type of solvent typically favors S N 1 reactions?
Polar protic solvents.
What is the role of NaN3 in the context of nucleophiles?
It acts as a nucleophile in reactions.
What must at least one step of the nucleophilic substitution reaction involve?
Inversion of configuration of the chirality center.
What is the relationship between soft nucleophiles and C(δ+)?
Soft nucleophiles have a strong affinity for C(δ+).
How are chirality centers indicated in the context of nucleophilic substitution reactions?
By asterisks.
What characterizes an S N 1 mechanism?
It involves a two-step process with the formation of a carbocation intermediate.
What do [CH3Br] and [OH-] represent in the rate equation?
[CH3Br] represents CH3Br concentration in molarity, and [OH-] represents OH- concentration in molarity.
What is the role of the incoming nucleophile in the S N 2 reaction?
It reacts with the alkyl halide or tosylate from the opposite direction of the leaving group.
How does the carbonyl group affect the acidity of the adjacent hydrogen in the E1cB reaction?
It makes the adjacent hydrogen unusually acidic by resonance stabilization of the anion intermediate.
What type of elimination reaction is likely to occur with a carbonyl compound and a strong base?
E1cB, leading to the formation of an alkene.
How many steps does the S N 2 reaction take?
It takes place in a single step without intermediates.
What is the primary difference between S N 1 and S N 2 reactions?
S N 1 is a two-step process, while S N 2 is a one-step process.
What is the relationship between stable carbocations and S N 1 reaction rates?
Higher stability of carbocations leads to a higher S N 1 reaction rate.
What is the effect of the solvent on S N 1 reactions?
Polar protic solvents stabilize the carbocation and the leaving group.
What is a common product of S N 1 reactions?
Racemic mixtures due to the planar nature of the carbocation.
What type of alkyl halide is a secondary alkyl halide?
An alkyl halide where the carbon attached to the halogen is bonded to two other carbon atoms.
What is the significance of CH3CN in nucleophilic reactions?
It is often used as a solvent and can act as a nucleophile.
Which mechanism is favored by tertiary substrates?
S N 1 mechanism.
What type of mechanism does S N 1 follow?
A two-step mechanism.
What type of solvent typically favors S N 2 reactions?
Polar aprotic solvents.
What does the constant 'k' represent in the rate equation?
The rate constant, which depends on various factors.
Which compound is a stronger nucleophile: DMSO or DMF?
DMSO.
