Question

How could IR spectroscopy distinguish between `CH_3CH_2CH_2OH` and `CH_3CH_2OCH_3`?

Answer 1

The IR spectrum of propan-1-ol would show a characteristic broad O-H stretching peak at 3200 to 3550 cm⁻¹. This peak would be absent in methoxyethane.

IR spectroscopy distinguishes compounds based on the vibrations of their bonds.

CH₃CH₂OCH₃ has C-C, C-H, and C-O bonds.

CH₃CH₂CH₂OH has C-C, C-H, C-O and O-H bonds.

So we look for the vibrational frequencies of an OH group.

The O-H group shows a characteristic broad stretching peak at 3200 to 3550 cm⁻¹.

The IR spectrum of propan-1-ol shows a broad peak centred at about 3350 cm⁻¹.

I couldn’t find a spectrum of methoxyethane, but the spectrum of methoxypropane, which should be similar, does not have this peak.