Q55 · 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 ${ }^{1} \mathrm{H} \mathrm{NMR}$ chemical shift values of methyl groups (in $\delta \mathrm{ppm}$ ), respectively, are 
(a)Cis; -5
(b)Trans; 17
(c)Cis; 17
(d)Trans; -5
Answer
Answer: D ✓ checked by 4AB · confidence high
Explanation
The photochemical 6π electrocyclisation is conrotatory and gives trans-15,16-dimethyldihydropyrene. Its internal methyls sit in the shielding ring current at about δ −4 to −5 (d).
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