Q8 · CSIR-NET Chemistry, June 2018
Paper: CSIR-NET June 2018 · Subject: Organic Chemistry · Chapter: Organic Spectroscopy · Topic: NMR 13C · Marks: 2 · Difficulty: Medium
Number of signals observed in the ${ }^{13} \mathrm{C} \mathrm{NMR}$ spectrum of the following compound is 
(a)4
(b)5
(c)6
(d)8
Answer
Answer (as printed): C
Explanation
The compound is bicyclo[2.2.2]octane-2,6-dione: both C=O groups are on different bridges but adjacent to the same bridgehead C-1. The only symmetry element is a mirror plane through C-1, C-4 and the unsubstituted bridge (C-7/C-8 lie in different environments).
Distinct carbons: C-1 (bridgehead next to both C=O), C-4 (other bridgehead), C-2/C-6 (two C=O, equivalent), C-3/C-5 (CH₂ next to C=O, equivalent), C-7 and C-8 (the two CH₂ of the third bridge, non-equivalent). Total = 6 signals in the ¹³C NMR spectrum. Answer (c).
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