Question 1

What descriptive term is applied to the type of diene shown in the structure above?

Accepted Answer

A conjugated diene

Question 2

Which of the following compounds has the smallest heat of hydrogenation, indicating the greatest stability?

Accepted Answer

(E)-2-methyl-2,4-hexadiene

Question 3

Rank the following dienes in order of increasing stability: trans-1,3-pentadiene, cis-1,3-pentadiene, 1,4-pentadiene, and 1,2-pentadiene.

Accepted Answer

1,2-pentadiene \u003c 1,4-pentadiene \u003c cis-1,3-pentadiene \u003c trans-1,3-pentadiene

Question 4

Among a series of isomeric trienes, the more negative the $$\Delta H^\circ of $$the hydrogenation reaction of a given triene, the ________ stable it is relative to the others in the isomeric series.

Accepted Answer

less

Question 5

Which of the following compounds is the most stable?

Accepted Answer

(E)-2-methyl-1,3-pentadiene

Question 6

When the relative energies of the s-cis and s-trans conformers of 1,3-butadiene are compared, one finds that ________.

Accepted Answer

the s-trans conformer is lower in energy than the s-cis

Question 7

What is the resonance energy of a system?

Accepted Answer

The energy difference between the actual molecule and the most stable contributing structure

Question 8

Which substrate would react most rapidly in an $$\mathrm{S_N2}$$ reaction?

Accepted Answer

$$\mathrm{CH_3CH_2CH=CHCH_2Br}$$

Question 9

When (S)-3-bromopent-1-ene is heated in water, which of the following compounds is NOT produced?

Accepted Answer

pent-4-en-1-ol

Question 10

Which of the following statements best explains why the double bond labeled 'A' in a conjugated diene reacts preferentially with 1 equivalent of HBr?

Accepted Answer

The resonance structures formed upon addition to double bond 'A' lead to a more stable carbocation intermediate.

Question 11

In a reaction where 1,3-butadiene reacts with Br$$_2 at $$low temperature, which product is expected to predominate?

Accepted Answer

The 1,2-addition product (kinetic product)

Question 12

Which of the following best describes the relationship between resonance energy and molecular stability?

Accepted Answer

Higher resonance energy means higher stability

Question 13

Which of the following is a correct statement about the heat of hydrogenation for conjugated versus isolated dienes?

Accepted Answer

Conjugated dienes have a lower heat of hydrogenation than isolated dienes

Question 14

Which of the following best explains why the s-trans conformer of 1,3-butadiene is more stable than the s-cis conformer?

Accepted Answer

The s-trans conformer has less steric hindrance between substituents

Organic Chemistry: Dienes, Stability, Resonance, and Reaction Mechanisms

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