Question 1

Which of the following statements about alkanes is correct?

Accepted Answer

The general formula for alkanes is $$\mathrm{C}_n\mathrm{H}_{2n+2}.$$

Question 2

Which of the following best explains why branched alkanes generally have lower boiling points than their straight-chain isomers?

Accepted Answer

Branched alkanes have weaker London dispersion forces due to decreased surface area.

Question 3

Given the following Newman projection of butane, which conformation is shown and what is its relative energy?

Accepted Answer

Gauche conformation; intermediate energy

Question 4

A student is asked to draw all possible structural isomers for C$$_5H$_{12}. $$How many unique isomers should they find?

Accepted Answer

3

Question 5

Which of the following statements about cyclohexane chair conformations is TRUE?

Accepted Answer

Bulky substituents prefer the equatorial position to minimize 1,3-diaxial interactions.

Question 6

Which of the following best describes a meso compound?

Accepted Answer

A compound with chiral centers and an internal plane of symmetry, making it achiral.

Question 7

A mixture contains 70% of one enantiomer and 30% of its mirror image. What is the enantiomeric excess (ee) of the mixture?

Accepted Answer

$$ee = 40\%$$

Question 8

Which of the following is the correct relationship between the equilibrium constant $$K_{eq}$$ and the standard free energy change $$\Delta G^\circ$$?

Accepted Answer

$$\Delta G^\circ = -RT \ln K_{eq}$$

Question 9

Which of the following best describes the rate-determining step in a multi-step reaction mechanism?

Accepted Answer

The slowest step with the highest activation energy barrier.

Question 10

A reaction has a $$\Delta G^\circ of$$ $$-10 kJ/$$mol. What does this indicate about the spontaneity and equilibrium of the reaction?

Accepted Answer

The reaction is spontaneous and favors products at equilibrium.

Question 11

Which of the following is a correct statement about optical activity?

Accepted Answer

A pure enantiomer rotates plane-polarized light, while a racemic mixture does not.

Question 12

Which of the following best describes the Hammond postulate?

Accepted Answer

The transition state of a reaction resembles the structure of the species (reactants or products) to which it is closer in energy.

Question 13

Which of the following is NOT a source of strain in cyclohexane conformations?

Accepted Answer

Hydrogen bonding between axial hydrogens.

Question 14

Which of the following statements about Fischer projections is correct?

Accepted Answer

Horizontal lines represent bonds coming out of the plane of the paper.

Question 15

A compound has two chiral centers and is found to have only three stereoisomers. What is the best explanation?

Accepted Answer

The compound has a meso form, reducing the number of stereoisomers.

Question 16

Which of the following factors will NOT increase the rate of a chemical reaction?

Accepted Answer

Increasing the activation energy.

Question 17

Which of the following best describes the difference between cis and trans isomers in cycloalkanes?

Accepted Answer

Cis isomers have substituents on the same side of the ring; trans isomers have them on opposite sides.

Question 18

Which of the following is the correct IUPAC name for the compound with the structure $$\mathrm{CH}_3\mathrm{CH}_2\mathrm{CH}_2\mathrm{CH}_3$$?

Accepted Answer

Butane

Question 19

If a reaction mechanism involves the formation of a carbocation intermediate, which of the following statements is most likely TRUE?

Accepted Answer

The rate-determining step is the formation of the carbocation.

Question 20

Which of the following is the best method to distinguish between enantiomers in the laboratory?

Accepted Answer

Measuring their optical rotation with plane-polarized light.

Organic Chemistry Exam 2 Study Guide: Alkanes, Stereochemistry, and Chemical Reactivity

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