Q55 · CSIR-NET Chemistry, June 2016
Paper: CSIR-NET June 2016 · Subject: Organic Chemistry · Chapter: Photochemical Reactions · Topic: Photocycloaddition · Marks: 2 · Difficulty: Hard
The correct match for the following transformations P-S with the processes I-IV is Reactions: 
(P) 
(Q) 
(R) 
(S) Processes: (I) Diels-Alder (II) Norrish Type-I (III) Photocycloaddition followed by Diels-Alder (IV) Norrish Type-II
(P) (Q) (R) (S) Processes: (I) Diels-Alder (II) Norrish Type-I (III) Photocycloaddition followed by Diels-Alder (IV) Norrish Type-II(a)P-II; Q-IV; R-III; S-I
(b)P-II; Q-IV; R-I; S-II
(c)P-IV; Q-II; R-III; S-I
(d)P-IV; Q-II; R-I; S-III
Answer
Answer: C ✓ checked by 4AB · confidence high
The source book printed D; on checking, C is correct — see the explanation.
Explanation
P, 4-heptanone giving 2-pentanone + ethylene, is Norrish II. Q, dibenzyl ketone giving bibenzyl + CO, is Norrish I. R is a benzene–maleic anhydride photo-[2+2] followed by Diels–Alder. S, the endoperoxide, is a Diels–Alder with singlet O₂ (c).
Study loop for Photochemical Reactions