Experimental Enthalpies of Formation and Strain of the Methylated 1-Amino-2-phenylethanes

The standard molar enthalpies of formation H _f ^00B0; (liq) at the temperature t = 298.15 K were determined using combustion calorimetry for N-methyl-3-methyl-3-phenyl-2-butaneamine 1a, N,N-dimethyl-3-methyl-3-phenyl-2-butaneamine 1b N-methyl-2,3-dimethyl-3-phenyl-2-butaneamine 2a, and N,N-dimethyl-2,3-dimethyl-3-phenyl-2-butaneamine 2b. The standard molar enthalpies of vaporization H _vap ^00B0; of these compounds were obtained from the temperature variation of the vapor pressure measured in a flow system. The following standard molar enthalpies of formation in gaseous phase H _f ^00B0; (g) are obtained from these data: for 1a – 10.9 ± 1.9; 1b – 3.6 ± 1.8; 1c – 26.6 ± 1.4, and 1d – 23.0 ± 1.8 kJ mol^–1. From the standard molar enthalpies of formation for gaseous compounds which are available in the literature, improved values for the increments of the Benson group addivitiy scheme of amines were calculated. They are used to determine the strain enthalpies of the amines 1 and 2 from this investigation.