Question 1

What descriptive term is applied to the type of diene represented by 2,4-hexadiene?

Accepted Answer

The term "conjugated diene" is applied to a diene in which the double bonds are separated by only one single bond and alternated with each other, such as in 2,4-hexadiene.

Question 2

Which of the following compounds contains the longest carbon-carbon single bond?

Accepted Answer

Ethane contains a single bond between its two carbon atoms, which is the longest carbon-carbon single bond. Allene, 1,3-butadiyne, 1,3-butadiene, and propyne all contain shorter carbon-carbon single bonds due to their triple or double bonds.

Question 3

Which of the following is a benzylic cation?

Accepted Answer

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Question 4

Among a series of isomeric trienes,the more negative the ΔH° of the hydrogenation reaction of a given triene,the ________ stable it is relative to the others in the isomeric series.

Accepted Answer

The answer of Among a series of isomeric trienes,the more...

Question 5

Which of the following is an allylic cation?

Accepted Answer

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Question 6

Draw the distribution of π electrons in the molecular orbitals of cyclobutadiene.

Accepted Answer

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Question 7

Which of the following is the most stable cation?

Accepted Answer

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Question 8

What is the hybridization of the central carbon of allene (1,2-propadiene)?

Accepted Answer

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Question 9

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

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Question 10

Which of the following numbered hydrogens is most easily abstracted by heterolytic cleavage? Explain.

Accepted Answer

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Question 11

Indicate whether the following molecule is aromatic,antiaromatic,or nonaromatic.

Accepted Answer

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Question 12

Which of the following compounds is more stable? Explain.

Accepted Answer

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Question 13

Which of the following is the most stable diene?

Accepted Answer

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Question 14

Which of the following is a cumulated diene?

Accepted Answer

A cumulated diene has all the carbon atoms in the double bond system adjacent to each other. In option C, there are two double bonds and all the carbon atoms are adjacent to each other, so it is a cumulated diene. Options A, B, D, and E have isolated double bonds, so they are not cumulated dienes.

Question 15

How many allylic hydrogen atoms are present in the following molecule?

Accepted Answer

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Question 16

Which species is represented by the following distribution of p electrons in the molecular energy diagram?

Accepted Answer

The diagram shows a total of 10 p electrons which means the species is a neutral carbon atom. Among the given options, only option C represents the molecular energy diagram of a neutral carbon atom.

Question 17

Which of the following is a conjugated diene?

Accepted Answer

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Question 18

Which of the following statements about the π molecular orbital description of cyclobutadiene is not correct?

Accepted Answer

This statement is incorrect. Cyclobutadiene has two degenerate bonding and antibonding π molecular orbitals. The four π electrons of cyclobutadiene would fit perfectly in the two bonding π molecular orbitals, resulting in a perfectly stable molecule. However, placing two electrons in the antibonding π molecular orbital would destabilize the molecule, making it antiaromatic. Therefore, cyclobutadiene is an example of an antiaromatic molecule.

Question 19

What descriptive term is applied to the type of diene represented by 1,5-octadiene?

Accepted Answer

Isolated dienes have double bonds separated by more than one single bond, as in 1,5-octadiene, where the double bonds are separated by two single bonds.

Question 20

How many benzylic hydrogens are present in the following molecule?

Accepted Answer

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Quiz 8: Delocalized Electrons: Their Effect on Stability, pka, and the Products of a Reaction - Aromaticity and Electronic Effects: an Introduction to the Reactions of Benzene