13C NMR spectra and structure of mono-, di- and trimethoxyphenylethylamines and amphetamines

Carbon-13 and proton chemical shifts of mono-, di- and trimethoxylated phenylethylamines (PEAs) and their hydrochlorides were determined and the signals were assigned and are reported. The data are interpreted to indicate that the side-chains of PEA derivatives and amphetamine salts have the amino and aromatic moieties predominantly trans (antiperiplanar), that ‘sandwiched’ OCH₃ groups and side-chains are forced out of the ring plane and that planar ortho-OCH₃ groups have their electron lone pairs oriented toward the side-chain and partially stabilize gauche rotamers. It is suggested that the location and density of electronic charges just outside the aromatic ring will significantly affect interactions with putative receptors.