Structural and conformational studies of N,N-dichloroethanamine and N,N-dichloro-2-propanamine by gas electron diffraction combined with ab initio calculations

The molecular structure and conformation of N,N-dichloroethanamine (EtNCl2, NDCEA) and N,N-dichloro-2-propanamine (i-PrNCl2:, NDCPA) were studied by g as electron diffraction. The optimized structures and the force constants o btained by MP2/6-31G** abinitio calculations were used in the analyses, The force constants were scaled to reproduce the vibrational wavenumbers of th e gas-phase infrared spectra measured in the present study. At room tempera ture, NDCEA exists in a conformational equilibrium of CI and C-s, forms and the abundance of the CI conformer is 79 +/-: 9%. The abundance of the C-1 for NDCPA is 88 +/- 12%. The structural parameters (r(g), and angle alpha,) for the CI conformer of NDCEA are as follows: r(N-C) = 1.479(6) Angstrom; r(C-C)= 1.542(7) Angstrom; (r(N-Cl)) :1.759(2) Angstrom; (r(C-H))= 1.107(8) Angstrom; LN-C-C 108.2(8)degrees; (angle C-N-Cl) 108.2(3)degrees; angle Cl -N-Cl = 106.9(2)degrees; phi C-C-N-Cl-g, = -76(2)degrees. Angle brackets de note averaged values and parenthesized values are the estimated limits of e rror (3 sigma) referring to the last significant digit. C1, means the C1 at om gauche to the C-C bond. Those for the C1 conformer of NDCPA are as follo ws: r(N-C) = 1.496(11) Angstrom; (r(C-C)) 1.762(2) Angstrom; (r(C-H)) = 1.1 19(5) A; (LN-C-C) 112.4(8)degrees; LC-C-C = 108.3(18)degrees; (angle C-N-Cl )= 109.1(6)degrees; angle Cl-N-Cl = 106.7(4)degrees; phi C-t-C-N-Cl-g 63(3) degrees. C-t means the C atom trans to the lone pair of the N atom, and C1, means the C1 atom gauche to the C-H bond of the alpha carbon.