Why does the gem-dimethyl groups appear as separate peaks in the proton NMR spectrum of isoborneol although they almost overlap in borneol?

Answer 1

short answer is think about the relative interactions each of the methyl groups see.

For borneol each methyl group sees very similar environments, the ALCOHOL is endo so it is far away from the methyl group closest to it, right??:) SO then each methyl group sees the CH--CH2 ring systems with the OH group being far away from the methyl group.

For ISoborneol the alcohol is much closer to the methyl group and makes it very different than the other methyl group that is on the other side (anti). In this case on methyl group sees the COH--C ring while the other sees CH2--CH2 groups

Answer 2

In isoborneol, the gem-dimethyl groups are non-equivalent due to the chiral center in the molecule, causing them to have different chemical environments and therefore exhibit as separate peaks in the NMR spectrum. In borneol, the gem-dimethyl groups are equivalent due to the molecule's symmetry, resulting in their signals overlapping as a single peak in the NMR spectrum.