Identify the products and explain their formation.
(a)
(b)
( c)
(d)
( e)
(f)
(g)
(h)
(i) .

Explanation

(a)
(b)
`gamma-`Hydroxy acid forms a more stable five-membered cyclic lactone.
( c) `(A)` is an anhydride which undergoes nucleophilic acyl substitution with amine. Necleophilic attack by amine occurs perferentially at the less-hindered `C-`atom of the formyl group. The leaving group is `MeCOO^(Ө)` ion.

(d) This problem is similar to problem `(c)` above. Here nuceophilic attack by amide takes place at the more-hindered side, since `F_3 c - COO^(Ө)` is a better leaving group than `MeCOO^(Ө)` ion.
( e) Here, a `beta`-lactone is formed, although `beta-`lactone is never formed from `beta-`hydroxy acid. The formation of `beta`-lactone in this case is due to the stabilisation of a carbocation through neighbouring group participation of `(COO^(Ө))` group.

(f) The protonation of `(C=C)` bond in `(A)` gives a stable benzyl carbocation `(I)` which forms `gamma-`lactone through neighbouring group participation of `(COO^(Ө))` group.

(f) The protonation of `(C=C)` bond on `(A)` gives a stable benzyl carbocation `(I)` which forms `gamma-`lactone through neighbouring group participation of `(COO^(Ө))` group.

(g) It is an example of Favorskii rearrangement reaction since both `(A)` and `(B)` are `alpha-`haloketones which on reaction with a base `(RO^(Ө))` give esters or with `overset (Ө) O H` give acid.
The formation of the same product by both `(A)` and `(B)` suggests that a common intermediate is formed.
Base `overset (Ө) O H` abstracts acidic `alpha-H` atom, following by an `SN^2` displacement of `Cl^(Ө)` to give a cyclopropan. one ring. Ring opening occurs to give a more stable benzylic carbanion.

(h) It is also an example of Favorskii rearrangement reaction, since the compound `(A)` is an `alpha`-haloketone. Base abstracks acidic `alpha-H` atom. followed by `SN^2`displacement of `Cl^(Ө)` to give a bicyclo ketone. Ring opening. followed by acidification, gives cyclopentane carboxylic acid `(B)`.

(i) The photochemical demerisation of cinnamic acid `(A)` is `[2 + 2]` cycloaddition reaction.