Chapter 20.8, Problem 14P

The following pKa values have been measured. Explain why a hydroxyl group in the para position decreases the acidity while a hydroxyl group in the meta position increases the acidity.

Dihydropyran is synthesized by treating tetrahydrofurfuryl alcohol with an arenesulfonic acid, ArSO3H. Propose a mechanism for this conversion.

H3C. H3C. CH3 nnc» XT :OH 2 CH₂OH HCI catalyst Aldehydes and ketones react reversibly with two equivalents of alcohol in the presence of an acid catalyst to give acetals. Alcohols are poor nucleophiles, and so protonation of the carbonyl oxygen is used to make the carbonyl carbon a stronger electrophile. Addition of the first equivalent of alcohol gives a hemiacetal, a hydroxyether. Addition of the second equivalent of alcohol is accompanied by loss of water to yield the product acetal. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instructions CH3 H3C CH3OH H3CQ OCH3 CH3 H3C. H HO: :OCH 3 CH3 46

H3C- H3C. OCH 3 H3CO CH3 H Aldehydes and ketones react reversibly with two equivalents of alcohol in the presence of an acid catalyst to give acetals. Alcohols are poor nucleophiles, and so protonation of the carbonyl oxygen is used to make the carbonyl carbon a stronger electrophile. Addition of the first equivalent of alcohol gives a hemiacetal, a hydroxyether. Addition of the second equivalent of alcohol is accompanied by loss of water to yield the product acetal. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instructions NA 2 CH₂OH HCI catalyst CH3 HỘ H3CQ H3C- H3CO CH3 H3C. OCH3 CH3 H₂O*: 45

Rank the reactivity of the compounds below toward nucleophilic acyl substitution by writing the compounds' letters in the proper blanks in the box below. `NH CI Br CH3 CH3 A В C E rank compounds for acyl substitution reactivity most least reactive reactive