Deck 17: Proton Nuclear Magnetic Resonance Spectroscopy

Question 1

List the following protons in order of increasing chemical shift (smallest shift first).

Answer 1

b > c > a, because of inductive effects.

Question 2

Pyrrole shows two principal CH signals in its NMR spectrum: at 6.5 ppm and 6.7 ppm. Is pyr- role an aromatic compound or a conjugated diene?

Answer 2

Absorption is downfield in the aromatic region; therefore, pyrrole is an aromatic compound.

Question 3

How many types of nonequivalent protons does each of the following compounds contain? (Example: CH₃CH₂Cl has two types, CH₃ and CH₂.)

Answer 3

(a) two
(b) three
(c) three
(d) two
(e) one

Question 4

In the preceding problem, determine the relative areas under the principal signals for each compound.

Question 5

5 What would be the splitting pattern (singlet, doublet, etc.) observed for each of the following indicated protons?

Question 6

A NMR spectrum shows a singlet at 7.3 ppm, a triplet at 4.3, a triplet at 2.9, and a singlet at 2.0. The relative areas are 5, 2, 2, and 3, respectively. Which of the following compounds is compat- ible with this spectrum?

Question 7

How would you distinguish between the following pairs of compounds using NMR spectros- copy? (Include in your answer the expected splitting patterns and relative areas of the NMR absorption.)

Question 8

The following types of protons (underlined) all show NMR absorption between d = 10-16 ppm. How would you use the infrared spectrum to identify the type of compound?