Q3. Arrange methanal, ethanal and propanone in order of increasing reactivity towards nucleophilic addition, and give two reasons.
Propanone < ethanal < methanal. Each extra alkyl group hinders the nucleophile’s approach and reduces the electrophilicity of the carbonyl carbon (NCERT page 236; reasoned).
Q4. Name the product when propanone reacts with hydroxylamine, and the product when it is heated with hydrazine and then KOH in ethylene glycol.
(i) Propanone oxime, (CH3)2C=N–OH. (ii) Propane, CH3CH2CH3: the Wolff–Kishner reduction turns >C=O into >CH2 (NCERT pages 238–239).
Q5. Which of hexan-2-one and hexan-3-one gives the iodoform test? Write the products.
Hexan-2-one, CH3COCH2CH2CH2CH3, which has a CH3CO group: it gives CHI3 and sodium pentanoate, CH3CH2CH2CH2COONa, one carbon fewer. Hexan-3-one, CH3CH2COCH2CH2CH3, has no methyl group on its carbonyl carbon (NCERT page 240; reasoned).
Q6. How many first-stage constitutional aldol condensation products can ethanal and butanal give with dilute alkali and heating, ignoring E/Z isomers and further reactions? Name them.
Four under these counting assumptions: each has one enolisable α-carbon and each can be attacked. Self products: but-2-enal (from two ethanal molecules) and 2-ethylhex-2-enal (from two butanal molecules). Cross products: hex-2-enal (ethanal’s enolate adds to butanal) and 2-ethylbut-2-enal (butanal’s enolate adds to ethanal) (reasoned from NCERT pages 241–242).
Q7. How would you tell benzaldehyde from propiophenone, C6H5COCH2CH3, using one test?
Tollens’ test: benzaldehyde gives a silver mirror; propiophenone, a ketone, does not. Fehling’s test would not do, since aromatic aldehydes do not respond to it, and neither would the iodoform test, since neither compound has a CH3CO group (NCERT pages 239–240; reasoned).