Chapter 14: Q41P (page 659)

Answer the following questions for each compound:
a. How many signals are in its ¹³C NMR spectrum?
b. Which signal is at the lowest frequency?

Short Answer

Expert verified

a)Number of signals for each compound

1) 3

2) 3

3) 2

4) 4

5) 3

6) 4

7) 3

8) 3

9) 2

b) An arrow indicates the lowest frequency signal carbon.

Step by step solution

Step-by-Step SolutionStep 1: Calculating number of signals

The number of different types of carbon present in a molecule gives the number of signals in a 13_C NMR spectrum. In spectra, signals are not split. The number of lines equals the number of signals. Number of signals for each compound is given below.

There are 3 carbons present in this compound. So, number of signal equals 3.

Equivalent carbon atoms in a molecule are calculated as one signal. So, in this compound, the first carbon is bonded to two CH₂ groups giving a total number of signals equal to 3.

CH carbon is attached to 2 CH₃ groups giving 3 signals to this molecule.

All the carbons are different in this compound, and it gives a total of 4 signals.

Two equivalent carbons ‘a’ and other carbon together gives 3 signals in ¹³C NMR spectrum

Chlorohexene compound gives 4 signals in 13C NMR spectrum. 2 pairs of equivalent carbon and other non-equivalent carbon together give 4 signals for this compound.

This compound shows 3 signals in ¹³C NMR spectrum

Both sides of this compound give equivalent protons. Thus, compound gives a total of 3 signals.

Bromoethene compound gives 2 signals.

Lowest frequency carbon in a compound

Carbon bonded to the electron withdrawing groups produce high frequency signals whereas, carbon in electron rich environment produce low frequency signals.

Lowest frequency signal – ‘a’