INVESTIGATION OF PYROLYSIS PRODUCTS OF PROPYLENIMINE BY GAS ELECTRON-DIFFRACTION COMBINED WITH AB-INITIO CALCULATIONS - MOLECULAR-STRUCTURES OF CH3-NH-CH=CH2 AND CH3-N=CH-CH3

Pyrolysis products of propylenimine have been investigated by gas elec tron diffraction aided by mass spectrometry. Propylenimine vapor was h eated in a quartz tube and effused into the diffraction chamber throug h a nozzle kept at room temperature, When the temperature of the quart z tube was 470 degrees C, propylenimine completely transformed into sy n- and anti-CH3-NH-CH=CH2 (N-methylvinylamine) and trans-CH3-N=CH-CH3 (N-methylethylidenimine), all of which are short-lived species. Geomet rical structures and mole fractions of these species were determined f rom electron diffraction data combined with the results of ab initio c alculations. The principal structural parameters of syn-CH3-NH-CH=CH2 are as follows: r(g)(N-C-vinyl) = 1.391(3) Angstrom; r(g)(N-C-methyl) = 1.465(3) Angstrom; r(g)(C=C) = 1.343(4) Angstrom; angle(alpha)CNC = 119.5(9)degrees; angle(alpha)NCC = 126.5(7)degrees. Those of anti-CH3- NH-CH=CH2 are as follows: r(g)(N-C-vinyl) = 1.395 Angstrom; r(g)(N-C-m ethyl) = 1.472 Angstrom; r(g)(C=C) 1.341 Angstrom; angle(alpha)CNC = 1 18.4 degrees; angle(alpha)NCC = 126.1 degrees. Those of trans-CH3-N=CH -CH3 are as follows: r(g)(N=C) = 1.278 Angstrom; r(g)(N-C) = 1.472 Ang strom; r(g)(C-C) = 1.511 Angstrom; angle(alpha)CNC = 118.0 degrees; an gle(alpha)NCC = 121.4 degrees. Parenthesized values are the estimated limits of error (3 sigma) referring to the fast significant digit. No error estimation is given for dependent parameters. The determined mol e fractions of syn- and anti-NMVA and trans-NMEI are 0.63(7), 0.28(8), and 0.09(4), respectively. The experimental data of electron diffract ion obtained at 530 degrees C could best be reproduced by partial incl usion (about 30%) of decomposition products such as ketenimine and met hane. The reaction path has been discussed on the basis of the tempera ture dependence of the amount of the unstable species.