Q: The position of triple bonds in alkynes can be determined through oxidative cleavage. If an unknown alkyne gives dodecanedioic acid ($$HOOC-(CH_2$)_{10}-COOH) $$after reaction with $$OsO_4$$ and $$H_2O$$, what is the most likely structure of the alkyne?

$$H_3C(CH_2$)_4-C \\equiv C-(CH_2$)_4CH_3$$

Question 1

In a multi-step reaction coordinate diagram, which letters typically represent the transition states, and how can you identify them?

Accepted Answer

The highest energy points (peaks) between intermediates.

Question 2

Given the following p$$K_a$$ values, which base(s) can deprotonate propanoic acid ($$pK_a = 4.88) in a $$reaction that favors product formation?

(i) $$CH_3O^-$$ ($$pK_a of$$ $$CH_3OH = 15.9)
(ii$$) $$NH_3$$ ($$pK_a of$$ $$NH_4^+ = 9.4$)
(iii) CH_3C$$ \	ext{C}^-$$ (pK_a$ of CH_3C$$ \text{CH} = 25$$)
(iv) CH_3CH_2OH$ (pK_a$ of CH_3CH_2OH_2^+ = -2.5$)
(v) H_2O$ (pK_a$ of H_3O^+ = -1.7$)
(vi) Br$$^-$$ (pK_a$ of $$HBr = -9$$)

Accepted Answer

Only (i), (ii), and (iii)

Question 3

In the reaction coordinate diagram, which step is the fastest?

Accepted Answer

The step with the lowest activation energy.

Question 4

Which intermediate in a reaction coordinate diagram is the most stable?

Accepted Answer

The intermediate with the lowest energy.

Question 5

At which carbon would an electrophile most likely attach in hex-1-en-5-yne, and why?

Accepted Answer

Carbon 1, due to the formation of a more stable carbocation.

Question 6

The position of triple bonds in alkynes can be determined through oxidative cleavage. If an unknown alkyne gives dodecanedioic acid ($$HOOC-(CH_2$)_{10}-COOH) $$after reaction with $$OsO_4$$ and $$H_2O$$, what is the most likely structure of the alkyne?

Accepted Answer

$$H_3C(CH_2$)_4-C \equiv C-(CH_2$)_4CH_3$$

Question 7

During the oxymercuration-demercuration of 1-ethyl-4-methylcyclohexene, which product(s) are formed?

Accepted Answer

Trans-2-ethyl-4-methylcyclohexanol and cis-2-ethyl-4-methylcyclohexanol

Question 8

When 1-methylcyclohexene reacts with $$H_2SO_4$$ and $$H_2O$$, what is the major product?

Accepted Answer

2-methylcyclohexanol

Question 9

Why does ring opening occur in opposite directions in the two reactions shown, one with a tetraalkylammonium group and one with an ethoxy group?

Accepted Answer

Because the tetraalkylammonium group stabilizes positive charge, while the ethoxy group is a weaker electron donating group.

Question 10

What is the expected product when 1-ethyl-2-vinylbenzene is treated with excess hot, concentrated potassium permanganate ($$KMnO_4$$)?

Accepted Answer

Benzoic acid and acetic acid

Question 11

Which of the following best explains why the $$S_N2$$ reaction of a 1° bromide by alkynide fails to give the desired product when the substrate contains an alcoholic proton?

Accepted Answer

Due to the presence of an acidic alcoholic proton in the substrate, an acid-base reaction will occur instead of a substitution reaction.

Question 12

Which acetylide ion and carbonyl compound can be used to synthesize 3,7-dimethyloct-4-yn-3-ol?

Accepted Answer

2,6-dimethylhept-3-yn-1-ide and acetone

Question 13

Which of the following bases would NOT be able to deprotonate propanoic acid ($$pK_a = 4.88$$)?

Accepted Answer

$$Br^-$$

Question 14

In the hydrogenation of 3,3-dimethyl-1-butyne with $$H_2$$, $$Pd/C$$, what is the final product?

Accepted Answer

3,3-dimethylbutane

Question 15

Which of the following statements about bond dissociation energy (BDE) is correct for a C–Br bond in a primary versus a tertiary carbon?

Accepted Answer

The C–Br bond in a primary carbon has a higher BDE than in a tertiary carbon.

Question 16

Which reaction conditions would favor the formation of a Markovnikov alcohol from an alkene?

Accepted Answer

$$H_2SO_4$$ and $$H_2O$$

Question 17

Which of the following is a correct statement about the regioselectivity of halohydrin formation from an alkene and $$Br_2$$/$$H_2O$$?

Accepted Answer

The hydroxyl group attaches to the more substituted carbon.

Question 18

Which of the following alkenes will only generate 2-bromo-3,3-dimethylpentane after reaction with HBr?

Accepted Answer

3,3-dimethyl-2-pentene

Question 19

Which of the following is the major product when but-1-yne is treated with $$HgSO_4/H_2SO_4$ and H_2O$?

Accepted Answer

Butan-2-one

Organic Chemistry Reaction Mechanisms and Concepts: Study Notes

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