Question 1

Which of the following statements best describes the first propagation step in the free-radical chlorination of cyclohexane?

Accepted Answer

A chlorine atom abstracts a hydrogen atom from cyclohexane, forming HCl and a cyclohexyl radical.

Question 2

When 2-methylbutane is heated with Br2, which carbon is most likely to be brominated in the major mono-substitution product?

Accepted Answer

The tertiary carbon (carbon 2), due to the stability of the tertiary radical.

Question 3

How many stereoisomers are possible for the dibromination of 2,3-dimethylbutane (ignoring enantiomers)?

Accepted Answer

2

Question 4

Which monomer is used to make the polymer polyvinyl chloride (PVC)?

Accepted Answer

Chloroethene ($$\mathrm{CH_2$=CHCl})$$

Question 5

For the allyl cation ($$\mathrm{H_2C=CH-CH_2$^+}$$), how many electrons are placed in the molecular orbital diagram, and which orbitals are occupied?

Accepted Answer

2 electrons occupy the lowest bonding ($$\pi) $$orbital; the non-bonding and anti-bonding orbitals are empty.

Question 6

Which molecule absorbs UV–visible light at the longest wavelength?

Accepted Answer

A molecule with the most extended conjugation, such as 1,3,5-hexatriene.

Question 7

Rank the following dienophiles for reactivity in the Diels–Alder reaction (1 = most reactive): $$\mathrm{CH_2$=CH_2$}$$, $$\mathrm{CH_2$=CHCN}$$, $$\mathrm{CH_2$=CHCO_2Me}.$$

Accepted Answer

$$\mathrm{CH_2$=CHCO_2Me}$$ \u003e $$\mathrm{CH_2$=CHCN}$$ \u003e $$\mathrm{CH_2$=CH_2$}$$

Question 8

Which nitrogen atom in histamine is LEAST basic, and why?

Accepted Answer

The nitrogen in the imidazole ring bonded to two carbons, because its lone pair is involved in aromaticity.

Question 9

Which of the following compounds is aromatic according to Huckel’s rule?

Accepted Answer

Cyclopentadienyl anion ($$\mathrm{C_5H_5^-})$$

Question 10

Using Frost’s circle, what is the electron configuration and aromaticity of the cyclopropenyl radical ($$\mathrm{C_3H_3^\bullet}$$)?

Accepted Answer

It has 3 $$\pi$$ electrons, does not satisfy Huckel’s rule ($$4n+2$$), and is anti-aromatic.

Question 11

Which is the least reactive toward electrophilic aromatic substitution?

Accepted Answer

Nitrobenzene ($$\mathrm{C_6H_5NO_2})$$

Question 12

Which is the correct IUPAC name for the compound with an amino group at position 1 and a nitro group at position 3 on benzene?

Accepted Answer

m-nitroaniline

Question 13

What is the hybridization of the oxygen atom in the resonance form of the acetate ion ($$\mathrm{CH_3COO^-}) $$where the negative charge is delocalized?

Accepted Answer

$$sp^2$$

Question 14

In the Diels–Alder reaction between 1,3-butadiene and maleic anhydride, which product is formed and what is its stereochemistry?

Accepted Answer

The endo product, with substituents syn to the bridge.

Question 15

Which of the following is a kinetic product in the addition of HCl to 1,3-butadiene?

Accepted Answer

1,2-addition product ($$\mathrm{CH_2ClCH=$$CHCH_3$$})$$

Question 16

Which of the following best describes the mechanism for the acetylation of benzene using AlCl3 and acetyl chloride?

Accepted Answer

The acetyl cation ($$\mathrm{CH_3CO^+}) is $$generated by reaction of acetyl chloride with AlCl3, then attacks benzene to form an arenium ion, which loses a proton to regenerate aromaticity.

Question 17

Which resonance structure of uracil best shows the delocalization of $$\pi$$ electrons within the aromatic ring?

Accepted Answer

A structure where the lone pair on the nitrogen forms a double bond, and the adjacent carbonyl oxygen receives a negative charge.

Question 18

Which of the following is NOT a requirement for aromaticity?

Accepted Answer

The molecule must have an even number of $$\pi$$ electrons.

Organic Chemistry Exam Study Guidance: Radicals, Resonance, Aromaticity, and Reactions

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