Question

Draw the expected broadband-decoupled ¹³C NMR spectra of the following compounds. Use Figure 13-41 (page 686) to estimate the chemical shift.

Short answer

In this molecule, only three carbons is present which are chemically equivalent. Hence three carbon peak is formed with different chemical shift.

Step-by-step solution

Broadband-decoupled 13C-NMR spectra

The ¹³C NMR spectra tell us about the carbon skeleton of organic molecules. The ¹³C-NMR spectra gives two main pieces of information:

1. The number of signals shows equivalent and different carbons or sets of carbons in molecules.
2. The splitting of a also shows, how many hydrogens are attached to each carbon atom.

All spin-spin interaction is suppressed (decoupled) in NMR spectroscopy approach, resulting in singlets for all signals.

Estimation of 13C-spectra of compound (a)

In this molecule total four carbon is present in the skeleton but only two peak is formed because two-carbon set (a, b)are equivalent.

Chemical shift:2C (75.5), 2C(125.9).

Estimation 13C-spectra of Compound (b)

In this molecule, total si carbon is present but only three^13C-NMR peak formed because in this organic skeleton three carbons set is present which is chemically equivalent.

Chemical shift:2C (22.4), 2C(24.9), 2C (126.0)

Estimation 13C-spectra of Compound (c)

In this molecule, five different carbons is present hence five peak is formed in the spectrum.

Chemical shift:1C (17.4), 1C(26.4), 1C (124.4), 1C(144.6), 1C (196.5).

Estimation 13C-spectra of Compound (c)

Chemical shift:1C (137.6), 1C(138.5), 1C (191.1).

In this molecule, only three carbons is present, which are chemically equivalent. Hence three carbon peak is formed with different chemical shifts.