A 13C and 15N experimental NMR and theoretical study of the structure of linear primary aliphatic amines and ammonium salts: from C1 to C18

Eighteen aliphatic linear amines, from methylamine to stearylamine, have been experimentally studied by NMR and theoretically calculated at the GIAO/B3LYP/6-311++G(d,p) level. A partial exploration of their conformation has been carried out, mainly to determine the effect on the chemical shifts. In solution and for neutral amines, 15N chemical shifts indicate a mixture of two conformations. In the solid state (CPMAS NMR) only the subset of solid amines has been studied (from C14 to C18). The 15N signals of the corresponding ammonium salts in the solid state depend on the counteranions, Cl− and CF3CO2−, a result that is theoretically proven.

Regular trends in linear amines for 13C and 15N NMR chemical shifts (in black) plus protonation effects (in red) in parts per million.