Q: Which of the following IR absorptions is most indicative of a carbonyl group (C=O)?

$$\text{Around } 1700\ \text{cm}^{-1}$$

Question 1

Which of the following statements best explains why alcohols often show a weak or absent molecular ion (M) peak in their mass spectra?

Accepted Answer

Alcohols fragment by losing water ($$M-18$$), resulting in a weak or absent M peak.

Question 2

A compound with the formula $$C_4H_9Br$$ shows two peaks of equal intensity at $$m/z = 137$$ and $$m/z = 139 in $$its mass spectrum. What does this indicate about the structure of the compound?

Accepted Answer

The compound contains a single bromine atom, which gives rise to the characteristic $$M$$ and $$M+2$$ peaks of equal intensity.

Question 3

Which of the following IR absorptions is most indicative of a carbonyl group (C=O)?

Accepted Answer

$$	ext{Around } 1700\ 	ext{cm}^{-1}$$

Question 4

In $$^1H $$NMR spectroscopy, a triplet signal integrating to 3 hydrogens is most likely due to which of the following groups?

Accepted Answer

A methyl group ($$CH_3) $$adjacent to a $$CH_2$$ group

Question 5

Which of the following statements about free radical halogenation of alkanes is correct?

Accepted Answer

The stability order of free radicals is: tertiary \u003e secondary \u003e primary.

Question 6

Which solvent is most appropriate for the formation of a Grignard reagent from an alkyl bromide?

Accepted Answer

Diethyl ether

Question 7

A substituted epoxide is treated with sodium methoxide ($$NaOCH_3) in $$methanol. Which carbon will the nucleophile preferentially attack?

Accepted Answer

The least substituted carbon of the epoxide

Question 8

Which of the following best describes the outcome when benzene is treated with $$CH_3Cl$$ and $$AlCl_3$$?

Accepted Answer

Benzene undergoes electrophilic aromatic substitution to form toluene.

Question 9

Which of the following substituents will most strongly deactivate a benzene ring toward electrophilic aromatic substitution when placed in the para position?

Accepted Answer

$$NO_2$$

Question 10

A benzene ring with a nitro group at the para position is treated with $$NaNH_2$$ and $$NH_3 ($$liquid). What is the most likely mechanism for the substitution of a halide on the ring?

Accepted Answer

Addition-elimination via a benzyne intermediate

Question 11

Which of the following carbonyl compounds is most reactive toward nucleophilic addition?

Accepted Answer

Aldehyde

Question 12

Which hydride reagent can reduce both esters and carboxylic acids to primary alcohols?

Accepted Answer

$$LiAlH_4$$

Question 13

A ketone is treated with a Wittig reagent ($$Ph_3P=CHR). $$What is the major product of this reaction?

Accepted Answer

An alkene

Question 14

Which of the following statements about the acidity of alpha hydrogens in carbonyl compounds is correct?

Accepted Answer

Alpha hydrogens are more acidic due to resonance stabilization of the enolate ion.

Question 15

In the aldol reaction, which of the following best describes the product formed when two molecules of acetaldehyde react under basic conditions?

Accepted Answer

A beta-hydroxy aldehyde

Question 16

Which of the following best explains why Gilman reagents ($$R_2CuLi) $$are used in coupling reactions with acyl halides?

Accepted Answer

They selectively replace the halide with an R group without further addition to the carbonyl.

Question 17

A substituted benzene ring with a methoxy group ($$OCH_3) at $$the para position is more reactive toward electrophilic aromatic substitution than benzene itself. What is the reason for this increased reactivity?

Accepted Answer

The methoxy group is an electron-donating group that activates the ring by resonance.

Question 18

Which of the following best describes the product of a Michael addition reaction?

Accepted Answer

A 1,4-addition product to an alpha, beta-unsaturated carbonyl compound

Question 19

When an ether is treated with concentrated $$HI$$, which of the following statements is correct regarding the mechanism?

Accepted Answer

If one R group can form a stable carbocation, the reaction proceeds via SN1; otherwise, it proceeds via SN2 at the least hindered carbon.

Question 20

Which of the following is true regarding the effect of substituents on the pKa of a carboxylic acid group on a benzene ring?

Accepted Answer

An electron-withdrawing group in the ortho or para position lowers the pKa, making the acid stronger.

Advanced Organic Chemistry: Spectroscopy, Free Radicals, Organometallics, Aromatics, and Carbonyl Chemistry

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