Question

A compound has an M+ ion at 132 amu. There is a peak at 133 amu whose intensity is 6.6% of the M+ peak and one at 134 amu whose intensity is 33% of the M+ peak. The only IR absorbances in the interpretable region (1500-4000 cm−1) are at 2900 and 1715 cm−1. The 13C NMR spectrum shows six resonances at δ 200 (s), 55 (d), 30 (t), 26 (t), 24 (t), and 20 (t). Draw a structure consistent with this information.

Answer 1

1.

MS spectrum of given compound shows molecular weight of 132 amu. Peak at M+2 = 134, having intensity of 33% indicates presence of one chlorine atom. Peak at M+1=133 having intensity of 6.6% indicates presence of six carbon atoms as obtained from following expression:

Number of carbon atoms = intensity of M+1 peak / 1.1

Number of carbon atoms = 6.6 % / 1.1

Number of carbon atoms = 6

Presence of six carbon atoms is further confirmed by presence of six peaks in 13C-NMR.

2.

IR absorption near 2900cm-1 indicates presence of aliphatic C-H stretching vibrations. IR absorption near 1715 cm^-1 indicates presence of carbonyl C=O stretching.

3.

13C-NMR shows a singlet at 200ppm, which can be attributed to carbonyl carbon of ketone. Doublet at 55 ppm indicates presence of carbon with one hydrogen and electron withdrawing group such as chlorine. Four triplets at 30, 26. 24 and 20, indicates presence of four CH2 groups.

Thus, based on above observations given compound is 2-chlorocyclohexan-1-one

CI 2-chlorocyclohexan-1-one