Question 1

Which of the following statements about resonance structures is CORRECT?

Accepted Answer

The actual molecule is a hybrid of all valid resonance structures, with delocalized electrons.

Question 2

Given the molecule 3-chloro-4,4-diethyl-2-methylhexane, which of the following is the correct IUPAC name for its constitutional isomer with the same number of carbons and chlorines but a different connectivity?

Accepted Answer

$$5-$$chloro-$$2-$$methyl-$$4,4-$$diethylhexane

Question 3

Which of the following best describes the most stable chair conformation of trans-1-ethyl-3-methylcyclohexane?

Accepted Answer

Both ethyl and methyl groups are equatorial.

Question 4

A molecule with the formula $$C_6H_{10}O_2$ shows IR absorptions at 1720$–1680$ cm$$^{-1}$$ and 3300$–2400$ cm$$^{-1}$$. Which functional groups are most likely present?

Accepted Answer

Carboxylic acid and ketone

Question 5

Which of the following is the correct number of possible stereoisomers for a molecule with three stereocenters and no internal plane of symmetry?

Accepted Answer

$$8$$

Question 6

Given the Fischer projection below, classify the configuration of the chiral center as $$R or$$ $$S$$:

$$\begin{array}{c}
\mathrm{CHO} \
| \
\mathrm{H} - \mathrm{C} - \mathrm{OH} \
| \
\mathrm{CH}_3
\end{array}$$

Accepted Answer

$$S$$

Question 7

Which of the following statements about Newman projections is TRUE?

Accepted Answer

The most stable conformation places the largest groups anti to each other.

Question 8

A molecule has the following IR absorptions: a strong, broad peak at $$3300 cm$^{-1}$$ and a sharp peak at $$2100 cm$^{-1}. $$Which functional groups are most likely present?

Accepted Answer

Alcohol and alkyne

Question 9

Which of the following is the correct line-angle structure for $$(R)-1$$,1-dimethyl-3-propylcycloheptane?

Accepted Answer

A cycloheptane ring with two methyl groups on C1 and a propyl group on C3, with the correct $$(R)$$ configuration at C3.

Question 10

Which of the following is the most stable resonance form for the acetate ion ($$CH_3COO^-$$)?

Accepted Answer

Both oxygen atoms share the negative charge equally, with one double bond and one single bond to carbon.

Question 11

Which of the following best describes the relationship between enantiomers and diastereomers?

Accepted Answer

Enantiomers are non-superimposable mirror images; diastereomers are not mirror images.

Question 12

Which of the following is the correct order of priority for the groups attached to a stereocenter according to the Cahn-Ingold-Prelog (CIP) rules?

Accepted Answer

The group with the highest atomic number has the highest priority.

Question 13

Which of the following molecules contains both an ester and an alkene functional group?

Accepted Answer

$$CH_2$$=$$CHCOOCH_3$$

Question 14

Which of the following is a correct statement about the stability of chair conformations in cyclohexane derivatives?

Accepted Answer

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

Question 15

A student draws a resonance structure for the nitrite ion ($$NO_2$$^-$$) with both oxygens single-bonded to nitrogen and a negative charge on each oxygen. What is the error in this resonance structure?

Accepted Answer

It violates the octet rule for nitrogen.

Question 16

Which of the following best describes the relationship between the two chair conformations of methylcyclohexane?

Accepted Answer

They are conformational isomers that interconvert via ring flip.

Question 17

Which of the following is the correct number of possible stereoisomers for a molecule with two stereocenters and a plane of symmetry?

Accepted Answer

$$2$$

Question 18

Which of the following is the correct line-angle structure for 5-chloro-2-methylheptane?

Accepted Answer

A seven-carbon chain with a chlorine on C5 and a methyl group on C2.

Question 19

Which of the following is the correct relationship between the enantiomer and the diastereomer of the following molecule?

$$\begin{array}{c}
	ext{Cyclopentanol with an OH group at C1 and a methyl group at C2}
\end{array}$$

Accepted Answer

They are stereoisomers but not mirror images.

Organic Chemistry Exam Study Guide: Resonance, Stereochemistry, Conformations, and Nomenclature

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