Chapter 26.SE, Problem 53AP

Interpretation Introduction

Interpretation:

Given that at room temperature the ¹HNMR spectrum of N,N-dimethylformamide shows three peaks at 2.9 δ (singlet, 3H), 3.0 δ (singlet, 3H) and 8.0 δ (singlet, 1H). With increase in temperature the two singlets at 2.9 δ and 3.0 δ slowly merge together. At 180oC, the ¹HNMR spectrum shows only two peaks at 2.95 δ (singlet, 6H) and 8.0 δ (singlet, 1H). This temperature dependence behavior is to be explained.

Concept introduction:

If two methyl groups attached to an atom in a single bond are non-equivalent because of a barrier to rotation of a single bond then the two methyl groups will give separate signals in ¹HNMR. However if the barrier is not there, free rotation becomes possible, the methyl groups become inter-convertible and the two signals will merge to a single signal.

To explain:

The temperature dependence behavior observed in the ¹HNMR spectrum of N,N-dimethylformamide is to be explained.