If you needed to distinguish each of the compounds in the following pairs ( A & B ) from each other, which spectroscopic method: infrared (IR), mass spectrometry (MS), ¹H nmr (NMR) or ultraviolet-visible (UV) would be best suited for this purpose? Assume that you do not have a reference sample of either compound for direct comparison.

Compound A Compound B IR MS NMR UV (CH3)2CHCH2-OH (CH3)3C-OH C2H5-Cl C2H5-Br