Question 1

Which of the following molecules is a meso compound?

Accepted Answer

2-bromo-2-chlorobutane

Question 2

How many stereoisomers are possible for a molecule with two chiral centers and no plane of symmetry?

Accepted Answer

$$4$$

Question 3

Which of the following best describes the difference between a reaction intermediate and a transition state?

Accepted Answer

Intermediates are local minima on the reaction coordinate, while transition states are maxima.

Question 4

In the addition of HBr to ethylene ($$CH_2$$=$$CH_2$$), how many transition states are present in the mechanism?

Accepted Answer

$$2$$

Question 5

Which of the following statements about meso compounds is correct?

Accepted Answer

Meso compounds have an internal plane of symmetry and are achiral.

Question 6

Given the molecule below, what is the configuration at the chiral center? (A benzyl group, ethyl group, hydrogen, and a lone pair on a carbon center)

Accepted Answer

$$S$$

Question 7

Which of the following best describes the nucleophile in the reaction between ethylene and HBr?

Accepted Answer

Ethylene, because it donates electrons from its $$\pi$$ bond

Question 8

What is the relationship between the following two molecules: (Both are 2-bromo-3-chloropentane, one with both substituents on wedges, the other with both on dashes)?

Accepted Answer

They are enantiomers

Question 9

Which of the following is the correct classification for the reaction: $$CH_3CH_2O^- + CH_3Br \rightarrow CH_3CH_2OCH_3 + Br^-$$?

Accepted Answer

Nucleophilic substitution (S_N2)

Question 10

In the reaction $$CH_2$$=$$CH_2 + $$HBr \rightarrow CH_3CH_2Br$$, which step involves the formation of a carbocation intermediate?

Accepted Answer

The $$\pi$$ electrons of ethylene attack $$H^+$$, forming a carbocation

Question 11

Which of the following best describes the flow of electrons in the reaction between ethylene and HBr?

Accepted Answer

The $$\pi$$ electrons of ethylene attack the hydrogen of HBr, and the electrons from the H-Br bond move to bromine

Question 12

Which of the following is true about Fischer projections?

Accepted Answer

Horizontal lines represent bonds coming out of the plane

Question 13

A molecule has two chiral centers and is a meso compound. How many stereoisomers are possible for this molecule?

Accepted Answer

$$2$$

Question 14

Which of the following is a correct statement about enantiomers?

Accepted Answer

They have identical physical properties except for the direction in which they rotate plane-polarized light

Question 15

Which of the following best describes the Markovnikov rule as applied to the addition of HBr to an alkene?

Accepted Answer

The hydrogen atom adds to the carbon with the most hydrogens already attached

Question 16

Which of the following is the correct IUPAC name for the molecule shown: (A five-carbon chain with a bromo on C2 and a chloro on C3)?

Accepted Answer

2-bromo-3-chloropentane

Question 17

Which of the following is NOT a characteristic of a transition state?

Accepted Answer

It is a stable species with a finite lifetime

Question 18

In a nucleophilic substitution reaction ($$S_N2$$), which of the following statements is correct?

Accepted Answer

The reaction proceeds with inversion of configuration at the stereocenter

Question 19

Which of the following best describes the electrophile in the reaction between ethylene and HBr?

Accepted Answer

HBr, because the hydrogen atom is electron-deficient

Question 20

Which of the following is a correct statement about diastereomers?

Accepted Answer

They have different physical properties

Organic Chemistry Exam Review: Stereochemistry, Reaction Mechanisms, and Molecular Classification

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