Question 1

Which of the following best describes an allylic carbocation?

Accepted Answer

A carbocation where the positive charge is directly on a carbon atom adjacent to a double bond.

Question 2

Which of the following resonance structures correctly represents the delocalization of charge in an allylic carbocation?

Accepted Answer

$$ \ce{CH2=CH-CH2^+} \leftrightarrow \ce{CH2^+-CH=CH2} $$

Question 3

A student is asked to predict the major product of the reaction between 1-butene and NBS (N-bromosuccinimide) in the presence of light. Which product will be formed?

Accepted Answer

$$ \ce{CH2=CH-CH(Br)-CH3}  ($$allylic bromination at the 3-position)

Question 4

Which statement best explains why allylic radicals are more stable than alkyl radicals?

Accepted Answer

Allylic radicals are stabilized by resonance, allowing the unpaired electron to be delocalized over multiple atoms.

Question 5

Which of the following is a correct resonance structure for the allylic anion formed from propene?

Accepted Answer

$$ \ce{CH2=CH-CH2^-} \leftrightarrow \ce{CH2^- -CH=CH2} $$

Question 6

In a reaction involving the formation of an allylic carbocation, which reagent would most likely facilitate this process?

Accepted Answer

A strong acid such as $$ \ce{HBr} $$

Question 7

Which of the following best describes the product of allylic bromination of cyclohexene using NBS and light?

Accepted Answer

Bromine adds to the allylic position to form 3-bromocyclohexene.

Question 8

Which of the following is the correct order of stability for the following carbocations: primary alkyl, allylic, tertiary alkyl?

Accepted Answer

Tertiary alkyl \u003e Allylic \u003e Primary alkyl

Question 9

A pharmaceutical chemist is designing a drug molecule with an allylic functional group. Which property is most likely to be enhanced by the presence of the allylic group?

Accepted Answer

Increased reactivity towards radical halogenation due to resonance stabilization.

Question 10

Which of the following best explains why NBS is used for allylic bromination instead of molecular bromine ($$ \ce{Br2} $$)?

Accepted Answer

NBS provides a low, steady concentration of $$ \ce{Br2} $$, favoring allylic substitution over addition to the double bond.

Question 11

Which of the following is a correct representation of an allylic radical?

Accepted Answer

$$ \ce{CH2=CH-CH2\cdot} $$

Question 12

A student proposes that the allylic position in a molecule is less reactive than the vinylic position in radical halogenation. Is this correct?

Accepted Answer

No, the allylic position is more reactive due to resonance stabilization of the radical.

Question 13

Which of the following molecules contains an allylic hydrogen?

Accepted Answer

$$ \ce{CH2=CH-CH3}  ($$propene)

Question 14

During the allylic bromination of cyclopentene with NBS and light, which intermediate is formed?

Accepted Answer

An allylic radical on the cyclopentene ring.

Question 15

Which of the following best describes the electronic structure of an allylic carbocation?

Accepted Answer

The positive charge is delocalized over two carbon atoms via resonance.

Question 16

A chemist is analyzing the reactivity of an allylic anion. Which statement is correct regarding its stability?

Accepted Answer

The allylic anion is stabilized by resonance, allowing the negative charge to be delocalized.

Question 17

Which of the following reactions is most likely to occur at the allylic position of an alkene?

Accepted Answer

Radical halogenation using NBS and light.

Question 18

Which of the following best describes the difference between allylic and benzylic positions?

Accepted Answer

Allylic positions are adjacent to a double bond, while benzylic positions are adjacent to an aromatic ring.

Allylic Carbocations and Allylic Radicals: Structure, Resonance, and Reactions

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