Question

Page 2 of 17 pages 1 Give brief, clear explanations for the following observations 120 marks total CH2 (a) The 13c NMR spectrum of isobutylbenzene, shown on the right, exhibits 7 resonances. CH CH 13] H3C ње (b) In the mass spectra of the three aliphatic alcohols 1-butanol, 2-butanol, and tert-butanol (CsH1o0 (molecular weight 74 g/mol) the molecular ion peaks are very small or non-existent. The base peaks in the spectra are miz 56 (1-butanol), 45 (2-butarnol), and 59 (tert-butanol), respectively CH3 CH3 [41 H2 H2 Hz

Answer 1

The C¹³ NMR of isobutylbenzene exhibits 7 resonances.

This is due to the presence of 7 different Carbon atoms present in the compound.

Totally 7 different environments are present.

Carbon a gives one resonance.

There are Two b carbons i.e. they are in similar environment they show one resonance.

Two c Carbons i.e. both the c carbons in similar environment they show one resonance.

D carbon and E carbon and F carbon shows one resonance each.

And Two g Carbons together shows one resonance.

Therefore totally 7 resonances are exhibited by Isobutylbenzene.