Q3. Give the products of (i) benzene with benzoyl chloride and anhydrous AlCl3; (ii) ethanenitrile with phenylmagnesium bromide, then H3O+.
(i) C6H5COC6H5, benzophenone (Friedel–Crafts acylation with an aroyl chloride, Ar–COCl). (ii) C6H5COCH3, acetophenone (Grignard reagent on a nitrile) (reasoned from NCERT page 234).
Q4. Which reagent turns pent-3-enenitrile, CH3CH=CHCH2CN, into pent-3-enal without touching the C=C bond?
Diisobutylaluminium hydride (DIBAL-H), then water: it reduces the nitrile to the imine, which water hydrolyses to the aldehyde, CH3CH=CHCH2CHO, and it leaves the C=C alone, as in NCERT’s example (NCERT page 232).
Q5. How would you make diethyl ketone, (C2H5)2CO, from propanoyl chloride, and why is a cadmium reagent used rather than the Grignard reagent itself?
Treat propanoyl chloride with diethylcadmium, (C2H5)2Cd, made from C2H5MgBr and CdCl2 (NCERT page 233). A Grignard reagent would attack the ketone as it formed (reasoned: Grignard reagents add to ketones, NCERT Unit 7, page 201), so the less reactive dialkylcadmium is used.
Q6. Ozonolysis of an alkene, followed by zinc dust and water, gives only propanone. Identify the alkene.
2,3-Dimethylbut-2-ene, (CH3)2C=C(CH3)2: each half of the double bond becomes a (CH3)2C=O (reasoned from NCERT pages 231–232).
Q7. What does dehydrogenation of propan-2-ol vapour over heated copper give, and why is this method used in industry?
Propanone: secondary alcohols give ketones over Ag or Cu. The method suits volatile alcohols and needs no oxidising agent, which is why it is an industrial method (NCERT page 231; reasoned).