i) Most aromatic acids are solids while acetic acid and others of its series are liquids. Explain why.
ii) Explain why ketones are less reactive towards nucleophiles than aldehydes.
ii) Explain why ketones are less reactive towards nucleophiles than aldehydes.
Solution
(i) Aromatic acids have higher molecular masses and flat rings that stack efficiently; with hydrogen-bonded dimers this gives strong crystal lattices — solids at room temperature. Lower aliphatic acids are light molecules — liquids.
(ii) In ketones two alkyl groups (a) donate electrons (+I), reducing the positive character of the carbonyl carbon, and (b) crowd the approach of the nucleophile. Aldehydes, with one H, are more electrophilic and less hindered — hence more reactive.
(ii) In ketones two alkyl groups (a) donate electrons (+I), reducing the positive character of the carbonyl carbon, and (b) crowd the approach of the nucleophile. Aldehydes, with one H, are more electrophilic and less hindered — hence more reactive.
CBSE Class 12 Board · 2002 · Delhi · Subjective