91Ó°ÊÓ

C NMR chemical shifts follow the same principles as those of ¹H, although the typical range of chemical shifts is much larger than for ¹H. The chemical shift reference standard for ¹³C is the carbons in tetramethylsilane (TMS), whose chemical shift is considered to be 0.0 ppm.

The assignment of the\(^1H\)NMR spectrum of the ketone A is as follows:

Assignment of the\(^1H\)NMR spectrum (a)

The assignment of the\(^{13}C\)NMR spectrum of the ketone A is as follows:

Assignment of the\(^{13}C\)NMR spectrum (a)

The key features of this\(^1H\)NMR spectrum are:

*The methyl protons marked at 1.15\(\delta \)as a 12H, doublet as the molecule under consideration is symmetric and the methyl protons are equivalent. There is one adjacent proton for each of these protons.

*The protons adjacent to the carbonyl group give a septet around\(\delta \)2.75. The value is high due to the electron-withdrawing effect of the carbonyl group. As there are 6 neighboring protons the multiplicity is 6+1=7.

(b) The assignment of the\(^1H\)NMR spectrum of the ketone B is as follows:

Assignment of the\(^1H\)NMR spectrum (b)

The assignment of the\(^{13}C\)NMR spectrum of the ketone B is as follows:

Assignment of the\(^{13}C\)NMR spectrum (b)

The key features of this\(^1H\)NMR spectrum are:

*The methyl protons at\(\delta \)1.05 as a 9H, singlet as tertiary butyl protons are equivalent. As there is no adjacent proton the peak will come as a singlet.

*The methyl protons adjacent to the carbonyl group give another singlet around\(\delta \)2.15. The value is high due to the electron-withdrawing effect of the carbonyl group.

*The methylene protons are marked to give a singlet around\(\delta \)2.35.

(c) The assignment of the\(^1H\)NMR spectrum of the ketone C is as follows:

Assignment of the\(^1H\)NMR spectrum (c)

The assignment of the\(^{13}C\)NMR spectrum of the ketone C is as follows:

Assignment of the\(^{13}C\)NMR spectrum (c)