A has a free OH and can therefore be the only structure to have both free OH stretch and bend present in the predicted spectrum. Isomer A is also the only structure whose predicted spectrum has two sets of doublets in the NH 2 / NH 3 bending/wagging mode region. The spectrum of isomer A appropriately reproduces the free NH stretch, NH 2 twist mode, and the majority of the relative intensity pattern of the IO stretching modes above 700 cm -1 .