Question 1

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

Accepted Answer

The chair conformation minimizes torsional strain and steric interactions.

Question 2

In the lower energy chair conformation of cis-1,3-dimethylcyclohexane, how many axial positions are occupied by hydrogen atoms?

Accepted Answer

5

Question 3

Which of the following is a propagation step in the free radical chlorination of dichloromethane?

Accepted Answer

$$\mathrm{CH_2Cl_2} + \mathrm{Cl^\cdot} \rightarrow \mathrm{CH_2Cl}^\cdot + \mathrm{HCl}$$

Question 4

How do alkyl substituents stabilize a carbocationic center to which they are attached?

Accepted Answer

Through an inductive donation of electron density to the cationic center

Question 5

Which of the following alkyl halides reacts most rapidly via an $$\mathrm{S_N2}$$ reaction with $$\mathrm{NaCN}$$?

Accepted Answer

1-iodobutane

Question 6

Which of the following species is the least nucleophilic?

Accepted Answer

$$\mathrm{BF_3$}$$

Question 7

Given the bond dissociation energies: $$\mathrm{CH_3$-Br}$$: 68 kcal/mol, $$\mathrm{CH_2Br-CH_2Br}$$: 65 kcal/mol, $$\mathrm{CH_3CH_2-Br}$$: 68 kcal/mol, which carbon-bromine bond is weakest?

Accepted Answer

Quaternary carbon

Question 8

Which of the following terms best describes the relationship between (2R,3S,4R)-2,3,4-trichlorheptane and (2S,3R,4R)-2,3,4-trichlorheptane?

Accepted Answer

Diastereomers

Question 9

Glucose has a specific rotation of $$+52.8^\circ. $$Predict the concentration of a glucose aqueous solution contained in a 10 cm long polarimetry tube if a rotation of $$+15.8^\circ$$ was observed. $$[\alpha] = \frac{\alpha_{obs}}{c \cdot l}$$

Accepted Answer

0.299 g/mL

Question 10

Which of the following is a secondary halide?

Accepted Answer

$$\mathrm{CH_3CH(Cl)CH_2CH_3}$$

Question 11

Which of the following is true for the initiation step of a free radical chlorination reaction?

Accepted Answer

$$\Delta H^\circ \u003e 0$$~and~$$\Delta S^\circ \u003c 0$$

Question 12

How many distinct dichlorination products can result when isobutane is subjected to free radical chlorination?

Accepted Answer

4

Question 13

List the following radicals in order of increasing stability: $$(\mathrm{CH_3$})_3C^\cdot$$, $$\mathrm{CH_2$=$$CHCH_2$$^\cdot}$$, $$\mathrm{CH_3CH_2^\cdot}$$, $$\mathrm{CH_3$^\cdot}$$, $$(\mathrm{CH_3$})_2CH^\cdot$$

Accepted Answer

$$\mathrm{CH_3$^\cdot} \u003c \mathrm{CH_3CH_2^\cdot} \u003c (\mathrm{CH_3$})_2CH^\cdot \u003c \mathrm{CH_2$=$$CHCH_2$$^\cdot} \u003c (\mathrm{CH_3$})_3C^\cdot$$

Question 14

Which of the following best describes the relationship between the two molecules shown below?

$$\mathrm{H_2C^*CH_2Br}$$ and $$\mathrm{H_2C^*CH_2Cl} ($$where $$^*$$ indicates a chiral center)

Accepted Answer

Diastereomers

Question 15

Which of the following is the major product when cyclohexene is treated with NBS and light in $$\mathrm{$$CCl_4$$}$$?

Accepted Answer

Allylic bromination at the position adjacent to the double bond

Question 16

Which of the following statements correctly describes the stereochemical configuration of D-Threonine ($$2R,3S$$)?

Accepted Answer

The configuration is $$2R,3S$$ and matches structure III.

Question 17

Which of the following is NOT a propagation step in the free radical chlorination of methane?

Accepted Answer

$$\mathrm{Cl_2$} + \mathrm{UV~light} \rightarrow 2\mathrm{Cl^\cdot}$$

Question 18

Which of the following best explains why tertiary alkyl halides do not undergo $$\mathrm{S_N2}$$ reactions efficiently?

Accepted Answer

Steric hindrance prevents nucleophilic attack at the tertiary carbon.

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