Q: Given the acid dissociation constant $$K_a$$ for acetic acid is $$1.8 \times 10$$^{-5}$$, what is the pK_a$?

$$pK_a = -\log_{10}(1.8 \times 10$$^{-5}$$) \approx 4.74$$

Q: A mixture contains 70% of the R enantiomer and 30% of the S enantiomer. What is the enantiomeric excess (ee)?

$$ee = \frac{70\% - 30\%}{100\%} \times 100 = 40\%$$

Question 1

Which of the following is the correct IUPAC name for a molecule with a five-carbon chain, a methyl group on the second carbon, and a double bond between carbons 2 and 3?

Accepted Answer

2-methylpent-2-ene

Question 2

Which statement best describes the difference between enantiomers and diastereomers?

Accepted Answer

Enantiomers are non-superimposable mirror images, while diastereomers are stereoisomers that are not mirror images.

Question 3

A compound has the following substituents on a double bond: on one carbon, a methyl and a hydrogen; on the other, an ethyl and a hydrogen. What is the E/Z configuration if the methyl and ethyl are on opposite sides?

Accepted Answer

E

Question 4

Which of the following best explains why cyclohexane adopts a chair conformation?

Accepted Answer

To minimize torsional and steric strain by maximizing staggered interactions

Question 5

Given the acid dissociation constant $$K_a$$ for acetic acid is $$1.8 	imes 10$$^{-5}$$, what is the pK_a$?

Accepted Answer

$$pK_a = -\log_{10}(1.8 	imes 10$$^{-5}$$) \approx 4.74$$

Question 6

Which of the following is true about optical activity?

Accepted Answer

A chiral compound rotates plane-polarized light, and a racemic mixture does not.

Question 7

A mixture contains 70% of the R enantiomer and 30% of the S enantiomer. What is the enantiomeric excess (ee)?

Accepted Answer

$$ee = \frac{70\% - 30\%}{100\%} 	imes 100 = 40\%$$

Question 8

Which of the following best describes the movement of electrons in a curly arrow mechanism for a nucleophilic substitution reaction?

Accepted Answer

Electrons move from the nucleophile to the electrophile, starting at a lone pair or bond.

Question 9

Which of the following is NOT a correct step in assigning E/Z alkene geometry?

Accepted Answer

Assign priorities based on mass number.

Question 10

Which of the following statements about Newman projections is correct?

Accepted Answer

They are used to visualize conformations and rotations about single bonds.

Question 11

A student is asked to draw the mechanism for the reaction of hydroxide ion with methyl bromide. Which arrow should be drawn first?

Accepted Answer

From the lone pair on the oxygen of hydroxide to the carbon of methyl bromide.

Question 12

Which of the following is a correct statement about diastereomers?

Accepted Answer

Diastereomers have different physical properties and are not mirror images.

Question 13

Which of the following is the correct formula for calculating enantiomeric excess?

Accepted Answer

$$ee = \frac{	ext{major} - 	ext{minor}}{	ext{major} + 	ext{minor}} 	imes 100$$

Question 14

Which of the following is a correct statement about assigning priorities in chiral centers?

Accepted Answer

Assign priorities based on atomic number: the higher the atomic number, the higher the priority.

Question 15

Which of the following is the correct relationship between p$$K_a$$ and acid strength?

Accepted Answer

Lower p$$K_a$$ values indicate stronger acids.

Question 16

Which of the following is a correct statement about conformational analysis of cyclohexane?

Accepted Answer

Bulky substituents prefer the equatorial position to minimize steric strain.

Question 17

Which of the following is NOT a type of isomerism described in the study materials?

Accepted Answer

Resonance isomerism

Question 18

Which of the following is the correct order for assigning IUPAC names?

Accepted Answer

Identify longest carbon chain, number to give lowest substituent numbers, assign substituents, assign R/S or E/Z, indicate positions for double/triple bonds.

Organic Chemistry Critical Concepts: Nomenclature, Isomerism, Stereochemistry, and Mechanisms

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