Q: In an E2 elimination reaction, which of the following is required for the reaction to proceed efficiently?

The leaving group and the $$eta-$$hydrogen must be antiperiplanar.

Q: Which product will be the major alkene when 2-bromopentane is treated with a strong base in an E2 reaction?

$$\mathrm{trans\text{-}2\text{-}pentene}$$

Q: Which region of the IR spectrum is most useful for identifying the presence of an O–H bond in an alcohol?

$$3200\text{–}3600\ \mathrm{cm}^{-1}$$

Q: When 2-butanol is treated with concentrated $$\mathrm{H_2SO_4}$$ and heated, which is the major product and why?

$$\mathrm{trans\text{-}2\text{-}butene}$$, because it is the more stable, more substituted alkene.

Question 1

Which of the following statements best explains why trans-2-butene is more stable than cis-2-butene?

Accepted Answer

Trans-2-butene has less steric hindrance between the methyl groups compared to cis-2-butene.

Question 2

In an E2 elimination reaction, which of the following is required for the reaction to proceed efficiently?

Accepted Answer

The leaving group and the $$eta-$$hydrogen must be antiperiplanar.

Question 3

Which product will be the major alkene when 2-bromopentane is treated with a strong base in an E2 reaction?

Accepted Answer

$$\mathrm{trans	ext{-}2	ext{-}pentene}$$

Question 4

A student is analyzing the $$^1H $$NMR spectrum of ethyl acetate ($$\mathrm{CH_3COOCH_2CH_3}). $$How many unique $$^1H $$NMR signals should they expect?

Accepted Answer

Four

Question 5

Which of the following statements about the E1 elimination mechanism is correct?

Accepted Answer

The rate-determining step involves the loss of the leaving group to form a carbocation.

Question 6

Which region of the IR spectrum is most useful for identifying the presence of an O–H bond in an alcohol?

Accepted Answer

$$3200	ext{–}3600\ \mathrm{cm}^{-1}$$

Question 7

When 2-butanol is treated with concentrated $$\mathrm{H_2SO_4}$$ and heated, which is the major product and why?

Accepted Answer

$$\mathrm{trans	ext{-}2	ext{-}butene}$$, because it is the more stable, more substituted alkene.

Question 8

Which of the following best describes the multiplicity of the $$^1H $$NMR signal for the methylene protons ($$\mathrm{CH_2$}) in $$ethanol ($$\mathrm{CH_3CH_2OH}$$)?

Accepted Answer

A quartet, due to coupling with three adjacent methyl protons.

Question 9

Which of the following alcohols will react fastest with HBr to form an alkyl bromide?

Accepted Answer

Tert-butyl alcohol ($$\mathrm{(CH_3$)_3COH})$$

Question 10

A compound shows a strong IR absorption at $$1715\ \mathrm{cm}^{-1}$$ and a broad absorption at $$3400\ \mathrm{cm}^{-1}. $$Which functional groups are present?

Accepted Answer

A carbonyl (C=O) and an alcohol (O–H)

Question 11

Which of the following statements about the conversion of alcohols to alkyl halides using HX is correct?

Accepted Answer

Primary alcohols react via an $$\mathrm{S_N2}$$ mechanism, while tertiary alcohols react via an $$\mathrm{S_N1}$$ mechanism.

Question 12

Which of the following best explains why the Zaitsev product is usually the major product in elimination reactions?

Accepted Answer

The Zaitsev product is the more substituted and thus more stable alkene.

Question 13

A student observes a $$^1H $$NMR signal at $$\delta = 9.8$$ ppm. Which functional group is most likely present?

Accepted Answer

An aldehyde

Question 14

Which of the following is a correct statement about the effect of electronegative atoms on $$^1H $$NMR chemical shifts?

Accepted Answer

Electronegative atoms deshield nearby protons, causing their signals to appear downfield (higher ppm).

Question 15

Which of the following best describes the mechanism for the dehydration of a secondary alcohol using $$\mathrm{H_2SO_4}$$?

Accepted Answer

Proton transfer, loss of leaving group to form a carbocation, then proton transfer to form the alkene.

Question 16

Which of the following statements about the $$^1H $$NMR spectrum of 1,1-dichloroethane ($$\mathrm{CH_3CHCl_2}) is $$correct?

Accepted Answer

There are two unique signals: a singlet for the methyl group and a quartet for the methine proton.

Question 17

Which of the following best describes the difference between E1 and E2 elimination mechanisms?

Accepted Answer

E1 is a two-step process involving a carbocation intermediate, while E2 is a concerted one-step process.

Question 18

A student treats 1-butanol with concentrated HBr. Which mechanism and product are expected?

Accepted Answer

$$\mathrm{S_N2}$$ mechanism, yielding 1-bromobutane

Question 19

Which of the following IR absorptions would indicate the presence of a triple bond (C≡C or C≡N) in a molecule?

Accepted Answer

$$2100	ext{–}2260\ \mathrm{cm}^{-1}$$

CHEM-245 Exam 3 Review: Elimination Reactions, NMR & IR Spectroscopy, and Alcohol Reactions

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