Q: Predict the major product for the following reaction: [Image 1: 2-bromo-3,3-dimethylpentane + $$NaOCH_3$$, $$HOCH_3$$, heat] Which alkene is the major product?

The more substituted (Zaitsev) alkene: $$\mathrm{2,3\text{-}dimethyl\text{-}2\text{-}pentene}$$

Question 1

Predict the major product for the following reaction:

[Image 1: 2-bromo-3,3-dimethylpentane + $$NaOCH_3$$, $$HOCH_3$$, heat]

Which alkene is the major product?

Accepted Answer

The more substituted (Zaitsev) alkene: $$\mathrm{2,3	ext{-}dimethyl	ext{-}2	ext{-}pentene}$$

Question 2

For the following reaction, what is the stereochemical outcome?

[Image 2: trans-1-bromo-2-methylcyclohexane + $$NaOCH_3$$, $$HOCH_3$$, heat]

Which statement is correct?

Accepted Answer

The product is a trans-alkene due to anti-coplanar elimination.

Question 3

Consider the following sequence:

[Image 3: 2-bromo-4-methyl-4-pentene (Br is wedge) + 1. $$\mathrm{H_2$, Ni} 2$$. $$\mathrm{EtOH, heat}$$]

What is the final product?

Accepted Answer

An alkene formed by elimination after hydrogenation of the double bond.

Question 4

Which sequence of reagents will convert a cyclohexanol (OH is wedge, adjacent H is dash) to a trans-alkene?

[Image 4: 1. $$\mathrm{$$PBr_3$$, base} 2$$. $$\mathrm{NaI} 3$$. $$\mathrm{EtONa, EtOH}$$]

What is the role of $$\mathrm{$$PBr_3$$} in $$this reaction?

Accepted Answer

It converts the alcohol to a bromide, making it a better leaving group.

Question 5

What is the function of $$\mathrm{CH_3SO_2Cl} ($$methanesulfonyl chloride) in the following reaction sequence?

[Image 5: 1. $$\mathrm{CH_3SO_2Cl, base} 2$$. $$\mathrm{NaI} 3$$. $$\mathrm{EtONa, EtOH}$$]

Accepted Answer

It converts the alcohol into a mesylate, a good leaving group.

Question 6

Predict the product for the following reaction:

[Image 6: 2-bromo-2-methylbutane + $$\mathrm{CH_3OH}$$]

What is the major organic product?

Accepted Answer

2-methoxy-2-methylbutane via $$\mathrm{S_N1}$$ substitution

Question 7

Which of the following is the correct rate law for an $$\mathrm{S_N2}$$ reaction?

Accepted Answer

$$\mathrm{rate = k[substrate][nucleophile]}$$

Question 8

What are four ways to turn an alcohol into a good leaving group?

Accepted Answer

Protonation with strong acid, conversion to tosylate, conversion to mesylate, or reaction with $$\mathrm{$$PBr_3$$}$$

Question 9

Draw all resonance structures for the benzylic carbocation shown below:

[Image 9: Benzyl carbocation]

What effect does resonance have on the positive charge?

Accepted Answer

Resonance delocalizes the positive charge over the aromatic ring, stabilizing the carbocation.

Question 10

Given the following compounds, which is the strongest acid?

[Image 10: a) $$\mathrm{CH_3CH_2OH} b$$) $$\mathrm{CH_3CO_2H} c$$) $$\mathrm{HC \equiv CH} d$$) $$\mathrm{CH_2$=CH_2$} e$$) $$\mathrm{CH_3CH_3}$$]

Accepted Answer

$$\mathrm{CH_3CO_2H} ($$acetic acid)

Question 11

In the reaction below, which side is favored at equilibrium?

[Image 11: Phenol + $$\mathrm{CH_3ONa}$$ $$\rightarrow$$ Sodium phenoxide + $$\mathrm{CH_3OH}$$]

Accepted Answer

The products are favored because phenol is more acidic than methanol.

Question 12

Which of the following carboxylic acids is the strongest acid?

[Image 12: a) $$\mathrm{CH_3CH_2CH_2CH_2CHFCO_2H} b$$) $$\mathrm{CH_3CHBrCH_2CH_2CO_2H} c$$) $$\mathrm{CH_3CH_2CH_2CHClCH_2CO_2H} d$$) $$\mathrm{CH_3CH_2CH_2CHFCH_2CO_2H} e$$) $$\mathrm{CH_3CH_2CH_2CHICH_2CO_2H}$$]

Accepted Answer

a) $$\mathrm{CH_3CH_2CH_2CH_2CHFCO_2H}$$

Question 13

Which of the following Fischer projections represents a meso compound?

[Image 13: Four Fischer projections labeled I, II, III, IV]

Accepted Answer

II

Question 14

Rank the following alcohols in decreasing order of acidity:

[Image 14: Three alcohols labeled I, II, III]

Accepted Answer

II \u003e I \u003e III

Question 15

Which of the following is the correct product for the reaction of 2-bromo-3,3-dimethylpentane with $$\mathrm{$$NaOCH_3$$} in$$ $$\mathrm{$$HOCH_3$$}$$ and heat?

[Image 7: Reaction scheme]

Accepted Answer

2,3-dimethyl-2-pentene

Question 16

What is the major product when 2-methyl-2-butanol is treated with $$\mathrm{H_2SO_4}$$?

[Image 8: Reaction scheme]

Accepted Answer

2-methyl-2-butene

Predicting Products of Organic Reactions: E2 Elimination and Substitution

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