Master Reaction Mechanisms in Chemistry: Online Quizzes and Study Guide

Question 1

Identify the defining feature of a nucleophilic reaction:

Accepted Answer

An electron-rich species initiates the reaction.

Answer

A new bond forms between the nucleophile and electrophile.

Answer

The nucleophile breaks a bond with the leaving group.

Answer

A carbocation intermediate forms.

Question 2

In an SN2 reaction, which step governs the reaction rate?

Accepted Answer

Nucleophile attacking the electrophile

Answer

Nucleophile formation

Answer

Leaving group dissociation

Answer

Rearrangement of the carbocation intermediate

Question 3

Predict the product of the reaction: CH3CH2Br + NaOH →

Accepted Answer

CH3CH2OH

Answer

CH3CH2Br

Answer

CH3CH=O

Answer

NaBr

Question 4

Identify the reagent class capable of facilitating elimination reactions:

Accepted Answer

Strong base

Answer

Strong acid

Answer

Oxidizing agent

Answer

Reducing agent

Question 5

State Zaitsev's rule:

Accepted Answer

In elimination reactions, the more substituted alkene is the major product.

Answer

In elimination reactions, the less substituted alkene is the major product.

Answer

In elimination reactions, the product alkene is always trans.

Answer

In elimination reactions, the product alkene is always cis.

Question 6

Predict the product of the Diels-Alder reaction: CH2=CHCH=CH2 + cyclopentadiene →

Accepted Answer

Norbornene

Answer

Cyclohexene

Answer

Cycloheptene

Answer

Cyclooctene

Question 7

Characterize an electrophilic reaction:

Accepted Answer

An electron-deficient species initiates the reaction.

Answer

A new bond forms between the electrophile and nucleophile.

Answer

The electrophile breaks a bond with the leaving group.

Answer

A carbocation intermediate forms.

Question 8

In an electrophilic aromatic substitution reaction, which step determines the reaction rate?

Accepted Answer

Electrophile attacking the aromatic ring

Answer

Electrophile formation

Answer

Leaving group dissociation

Answer

Rearrangement of the carbocation intermediate

Question 9

Select the correct mechanism for the nucleophilic substitution reaction of an alkyl halide with an alkoxide ion:

Accepted Answer

SN2

Answer

SN1

Answer

E1

Answer

E2

Question 10

In an E2 elimination reaction, which step determines the reaction rate?

Accepted Answer

Removal of a proton from the beta-carbon

Answer

Removal of the leaving group

Answer

Formation of the double bond

Answer

Alignment of the orbitals

Question 11

Provide an example of a cycloaddition reaction:

Accepted Answer

Diels-Alder reaction

Answer

Claisen condensation

Answer

Wittig reaction

Answer

Michael addition

Question 12

Distinguish between a heterocycle and a carbocycle:

Accepted Answer

Carbocycles contain only carbon atoms, while heterocycles contain heteroatoms.

Answer

Heterocycles contain only carbon atoms, while carbocycles contain heteroatoms.

Answer

Heterocycles are cyclic compounds, while carbocycles are acyclic compounds.

Answer

Carbocycles are cyclic compounds, while heterocycles are acyclic compounds.

Question 13

State Markovnikov's rule:

Accepted Answer

In an addition reaction of an unsymmetrical alkene, the electrophile adds to the carbon atom with the most hydrogen atoms.

Answer

In an addition reaction of an unsymmetrical alkene, the electrophile adds to the carbon atom with the least hydrogen atoms.

Answer

In an elimination reaction, the proton is removed from the carbon atom bonded to the most electronegative group.

Answer

In an elimination reaction, the proton is removed from the carbon atom bonded to the least electronegative group.

Question 14

Which type of organic reaction involves breaking a sigma bond and forming a pi bond?

Accepted Answer

Elimination

Answer

Addition

Answer

Substitution

Answer

Cycloaddition

Question 15

Identify the definition of a resonance structure:

Accepted Answer

A structure that represents the delocalization of electrons over several atoms

Answer

A structure that represents the highest energy state of a molecule

Answer

A structure that represents the lowest energy state of a molecule

Answer

A structure that represents the transition state of a reaction

Question 16

Which characteristic distinguishes nucleophilic reactions?

Accepted Answer

Attack on a positive or partially positive center.

Answer

Utilize a Lewis acid as a catalyst.

Answer

Form a new carbon-carbon bond.

Answer

Involve the transfer of a proton.

Question 17

Identify an example of an electrophilic addition reaction.

Accepted Answer

Addition of HBr to an alkene.

Answer

Addition of NH3 to a ketone.

Answer

Substitution of a hydroxyl group with a chlorine atom.

Answer

Rearrangement of a carbocation.

Question 18

Which of the following accurately describes the mechanism of the reaction between an alkyl halide and a nucleophile?

Accepted Answer

Nucleophilic attack on the electrophilic carbon, resulting in bond formation and inversion of configuration at the reaction center.

Answer

Radical attack on the electrophilic carbon, leading to the formation of a new radical species.

Answer

Electrophilic attack on the nucleophilic carbon, leading to bond formation.

Answer

Carbocation formation followed by nucleophilic attack, resulting in retention of configuration.

Question 19

In an E2 elimination reaction, which step is rate-determining?

Accepted Answer

Formation of the transition state involving the proton and base, where bond breaking and formation occur simultaneously.

Answer

Formation of the carbocation intermediate, which is a high-energy species.

Answer

Departure of the leaving group, resulting in the formation of a carbocation intermediate.

Question 20

In the Diels-Alder reaction between cyclopentadiene and methyl acrylate, what is the expected major product?

Accepted Answer

A six-membered cyclic product formed through a concerted cycloaddition.

Answer

A four-membered cyclic product resulting from an alternative cycloaddition pathway.

Answer

No reaction, as the reactants are not compatible for a Diels-Alder reaction.

Answer

A polymer product formed through a chain-propagation mechanism.

Question 21

Which characteristic is distinctive of radical reactions?

Accepted Answer

Chain propagation steps, where reactive intermediates react with stable molecules to generate new reactive intermediates, leading to chain reactions.

Answer

Stereospecific products, where the stereochemistry of the starting material is preserved in the product.

Answer

Base-catalyzed, where a base is required to initiate or facilitate the reaction.

Answer

High activation energy, indicating a slow reaction rate.

Question 22

What is the major product of the following reaction: CH3CH=CH2 + HBr → ?

Accepted Answer

CH3CHBrCH3, resulting from the Markovnikov addition of HBr to the alkene.

Answer

CH3CBr=CH2, suggesting rearrangement of the alkene prior to reaction with HBr.

Answer

CH3CH2CH2Br, resulting from anti-Markovnikov addition of HBr to the alkene.

Answer

CH2=CHCH2Br, indicating no reaction between the alkene and HBr.

Question 23

In an electrophilic aromatic substitution reaction, which species is the most reactive electrophile?

Accepted Answer

Nitronium ion (NO2+), a highly electrophilic species generated from nitric acid.

Answer

Chlorine molecule (Cl2), a moderately reactive electrophile that can undergo electrophilic aromatic substitution but is less reactive than NO2+.

Answer

Bromine molecule (Br2), an even less reactive electrophile than Cl2.

Answer

Iodine molecule (I2), a relatively weak electrophile that undergoes electrophilic addition rather than substitution.