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 gas electron diffraction. The optimized structures and the force constants obtained by MP2/6-31G** ab initio calculations were used in the analyses. The force constants were scaled to reproduce the vibrational wavenumbers of the gas-phase infrared spectra measured in the present study. At room temperature, NDCEA exists in a conformational equilibrium of C 1 and C s forms and the abundance of the C 1 conformer is 79 ± 9%. The abundance of the C 1 for NDCPA is 88 ± 12%. The structural parameters (r g and ∠α) for the C 1 conformer of NDCEA are as follows: r(N−C) = 1.479(6) Å; r(C−C) = 1.542(7) Å; 〈r(N−Cl)〉 = 1.759(2) Å; 〈r(C−H)〉 = 1.107(8) Å; ∠N−C−C = 108.2(8)°; 〈∠C−N−Cl〉 = 108.2(3)°; ∠Cl−N−Cl = 106.9(2)°; φ C−C−N−Clg = −76(2)°. Angle brackets denote averaged values and parenthesized values are the estimated limits of error (3σ) referring to the last significant digit. Clg means the Cl atom gauche to the C−C bond. Those for the C 1 conformer of NDCPA are as follows: r(N−C) = 1.496(11) Å; 〈r(C−C)〉 = 1.531(6) Å; 〈r(N−Cl)〉 = 1.762(2) Å; 〈r(C−H)〉 = 1.119(5) Å; 〈∠N−C−C〉 = 112.4(8)°; ∠C−C−C = 108.3(18)°; 〈∠C−N−Cl〉 = 109.1(6)°; ∠Cl−N−Cl = 106.7(4)°; φ Ct−C−N−Clg = 63(3)°. Ct means the C atom trans to the lone pair of the N atom, and Clg means the Cl atom gauche to the C−H bond of the α carbon.