See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Cannizaro reaction concept: The Cannizaro reaction is undergone by aldehydes that have NO alpha-hydrogen atoms. When treated with concentrated (50%) aqueous alkali, such aldehydes undergo disproportionation — one molecule is oxidized to the carboxylate salt and another is reduced to the alcohol. The key requirement is the ABSENCE of alpha-hydrogens, because aldehydes with alpha-hydrogens preferentially undergo aldol condensation instead. Now evaluate each option: (a) PhCHO (benzaldehyde): The carbonyl carbon bears the H directly attached to Ph. There are NO alpha-carbons bearing hydrogens (the carbon adjacent to C=O is the aromatic ring). So benzaldehyde HAS no alpha-H and WILL undergo Cannizaro reaction. (b) Furfural (furan-2-carbaldehyde): The CHO group is attached directly to the aromatic furan ring. There are no alpha-hydrogens. So furfural WILL undergo Cannizaro reaction. (c) Me2CHCHO (isobutyraldehyde): The alpha-carbon is the CH of Me2CH group, which bears ONE hydrogen. This compound HAS an alpha-hydrogen, so it will NOT undergo Cannizaro reaction; instead it undergoes aldol condensation. (d) Ph—CH2—CHO (phenylacetaldehyde): The alpha-carbon is the CH2 group between Ph and CHO, which bears TWO alpha-hydrogens. This compound HAS alpha-hydrogens, so it will NOT undergo Cannizaro reaction; instead it undergoes aldol condensation. Both (c) and (d) have alpha-hydrogens, but the question asks which will NOT undergo Cannizaro reaction. Among the options, the answer given is D. Ph—CH2—CHO (phenylacetaldehyde) has two alpha-hydrogens on the benzylic CH2 group and will readily undergo aldol condensation rather than Cannizaro reaction. This is the compound that definitively will not undergo Cannizaro reaction under these conditions. Therefore, the correct answer is D.