Edexcel IAL Chemistry 15.8 Reactions of carbonyl compounds

Use the reagent and observation to decide whether the compound is an aldehyde, ketone or methyl ketone, then connect product structure to reduction or CN- attack.

Exam points

Distinguish aldehydes and ketones using Tollens, Fehling, Benedict or dichromate results.
Use 2,4-DNPH and iodoform observations to confirm carbonyls or methyl ketones.
Draw HCN nucleophilic addition mechanisms with CN- attack, dipoles and curly arrows.

[Maximum number: 4]

This question is about carbonyl compounds.

(a)

Three carbonyl compounds, A, B and C, are straight-chain structural isomers, with the formula $\mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}$ .
Only isomer A reacts with Tollens' reagent to give a silver mirror.
Only isomer B reacts with iodine in the presence of alkali to produce pale yellow crystals.

Draw the displayed structures of these three isomers.

Figure for Question (a) — Edexcel A-Level Chemistry A2

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(b)

Propanone, an isomer of propanal, also reacts with HCN in the presence of KCN.

Draw the skeletal formula of the product of this reaction.

[ 1 ]

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15.8—The reactions of carbonyl compounds with: i Fehling’s or Benedict’s solution, Tollens’ reagent and acidified dichromate(VI) question 1

Question (a)

Question (b)