On the existence of intramolecular hydrogen bonds in methyl o-mercaptobenzoate and 2-methoxymethylbenzenethiol

Full analyses of the 1 H nmr spectra of methyl o-mercaptobenzoate and of 2-methoxymethylbenzenethiol yield spectral parameters suggesting that the trans conformer of the former is preferred by 1.6 ± 0.7 kJ/mol in free energy in solution at 305 K. Both cis and trans conformers can be reasonably discussed in terms of "planar" conformations. The ether displays nearly equal concentrations of cis and trans conformers. However, these conformers display considerable conformational freedom of the sulfhydryl group. These results are compared to previous infrared data. It is suggested that in the ester the small tendency towards intramolecular hydrogen bonding involves the carbonyl oxygen. Any interaction in the ether must surely occur for conformations in which the SH and CO bonds are far from the ring plane.