[42NSL]

For two different compounds with the same molecular formula, such as propanoic acid and methyl ethanoate, is is possible to distinguish the members of each pair with IR?

[discodermolide]

For two different compounds with the same molecular formula, such as propanoic acid and methyl ethanoate, is is possible to distinguish the members of each pair with IR?

Yes it is, just look at the structures and you will see the differences. Check against the IR frequencies.