Q6 · CSIR NET Chemistry, December 2018
Paper: CSIR NET December 2018 · Subject: Organic Chemistry · Chapter: Organic Spectroscopy · Topic: NMR 1H · Marks: 2 · Difficulty: Hard
The compound P undergoes a pericyclic reaction under photochemical conditions to give compound Q. In compound Q, the relative stereochemistry and ${}^{1}\mathrm{H}$ NMR chemical shift values of methyl groups (in $\delta$ ppm), respectively, are 
(a)Cis; -5
(b)Trans; 17
(c)Cis; 17
(d)Trans; -5
Answer
Answer: D ✓ checked by 4AB · confidence high
Explanation
Photochemical 6π electrocyclisation of the metacyclophanediene is conrotatory and gives trans-15,16-dimethyldihydropyrene. Its internal methyls sit in the shielding zone of the aromatic 14π ring current, at δ ≈ −4 to −5 (d).
Study loop for Organic Spectroscopy