DAT Question of the Day

Correct Answer: E. Addition of a nucleophile to the carbonyl is followed by loss of the leaving group.

Carbonyl compounds react with nucleophiles via an addition mechanism: the nucleophile attacks the carbonyl carbon, forming a tetrahedral intermediate. The tetrahedral intermediate itself can be an alcohol or alkoxide, depending on the pH of the reaction. The tetrahedral intermediate of an acyl compound contains a substituent attached to the central carbon that can act as a leaving group. After the tetrahedral intermediate forms, it collapses, recreating the carbonyl C=O bond and ejecting the leaving group in an elimination reaction. In nucleophilic acyl substitution, the leaving group is ejected in a separate exothermic step. The Hammond Postulate predicts that the transition state for this step resembles the tetrahedral intermediate. Therefore, in the transition state for this step minimal bond breaking has occurred, and the importance of the nature of the leaving group is diminished.

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Correct Answer: C. 3

Catalytic hydrogenation reactions lead to a cis addition of hydrogen, or in this case deuterium atoms

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Correct Answer: D. 4

Aromatic compounds are named as derivatives of benzene. Substituents positions are indicated by numbers except that o- (ortho), m- (meta) and p- (para) may be used in place of 1,2-, 1,3-, and 1,4-, respectively, when only two substituents are present. If alkyl substituents are smaller than the ring (6 or fewer carbons), the compound is considered an alkyl substituted benzene. Alkyl substituents larger than the ring (7 or more carbons), are phenyl-substituted alkanes. Compounds are named by numbering the position of each so that the lowest possible numbers are used. The substituents are listed alphabetically when writing the name.

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