Question

Which of the following compounds would not be represented by a lone singlet in the proton NMR?

benzene

cyclohexane

dimethyl ether (CH3-O-CH3)

1,2-ethanediol

None of these choices.

Answer 1

Explanation:

1. Benzene will show singlet for all 6 H at 7.00 ppm.
2. Cyclohexane undergoes rapid flipping of ring at r.t. hence axial and equatorial both groups of proton will exhibit single peak. But at very low temperature conformations get locked in any one of the situation shown in image. And hence 2 peaks observed in H1-NMR.

Axial protons appear high field (low delta value) than equatorial protons.

1. In Ethane diol 2 peaks of proton possible. One for Oh protons in the range 0.5-5.0 0ppm a broad single peak. And Anathor peak at about 3.9 ppm for CH2 protons attached to OH group.