Chapter 15: Q55P (page 732)

How could you use ¹H NMR spectroscopy to distinguish the following esters?

Short Answer

Expert verified

The four facets of proton NMR spectroscopy are-

The number of signal sets- the number of unique hydrogen types.
The chemical shifts (frequency) of each signal set- the chemical environment, hybridization and functional group dependent.
The integration of each signal set- How many hydrogen atoms cause a signal.
3H- CH₃group
2H- CH₂ group
1H- CH or -OH group.
The splitting of each signal set- it gives the idea of what is connected to a given carbon.

N line- N-1 neighbour hydrogens (in spectrum).
N neighbours- N+1 lines or signals (when structure of the compound is known and we are trying to find what the spectrum would look like).

The frequency of a signal is proportional to the number of hydrogen atoms (neighbouring hydrogen atoms +1) corresponding to that signal.

Step by step solution

Distinguishing esters based on proton NMR spectroscopy

B can be distinguished from the rest of the three A,C and D because B has 4 signals while the rest have three signals. Now, D can be distinguished from A and C on the basis of the splitting present. The three signals in D are singlet (1 line), doublet (2 lines), and septet (7 lines) while the signals in A and C are singlet (1 line), quartet (4 lines), and triplet (3 lines).

Now, these A and C can be distinguished from each other on the basis of frequency, the highest frequency signal in A is a singlet whereas the highest frequency signal in C is a quartet.