Triaziridines. Part III. Triaziridine, azimine, and triazene: A SCF study of the energy and structure of N₃H₃‐isomers

Abstract

The portions of the N,H, singlet potential energy surface corresponding to triaziridines (l), azimines (2) and triazenes (3) have been calculated by ah initio SCF using 3-21G, 6-31G, and 6-31G** basis sets. Minima and transition states were located by force gradient geometry optimization. The most important computation results are: 1) Triaziridines (1): The configuration at the 3 N-atoms is pyramidal. There are 2 stereoisomers, l a and lb. The c,t-isomer l a has less energy than the c,c-isomer lb. The 2 stereoisomerizations by N-inversion have rather high activation energies. The N,N bonds in 1 are longer and weaker (STO-3G estimation) than in hydrazine. The Nhomocycle 1 exhibits less ring strain than the C-homocycle cyclopropane or threemembered heterocycles. 2) Azimine (2): All 6 atoms are in the same plane. There are 3 stereoisomers, 2a, 2b, and 2c. The order of ground state"energies is ' ) Part 11, see [I]. ' )

Triaziridines. Part V. A semiempirical MNDO study of nitrogen inversion and amide rotation in Formyltriaziridines

“…The i-Pr-bearing N (2) and N(3) of 3 are somewhat more flattened than the N-atoms in 1. This effect, which is more pronounced in 3a and 3c with their cis-related i-Pr groups, may be due to steric bulk of the N-substituents; the relatively large (i-Pr)-N(2)-N(3) and (i-Pr)-N(3)-N(2) bond angles of about 127" in 3a and 3c point in the same direction.…”

“…- Table I shows the results of our MNDO calculations on the ground-state structure of the two stereoisomers of 1 together with our previous results [2] of ab initio SCF calculations using the 6-31G basis set (the best data available). As can be seen, the two methods lead to rather similar results, insofar as the N-N bond lengths differ by not more than 4%, the degree of N-pyramidality by not more than 3 YO, and the differences in energies5) by not more than 17 % (6-3 1G//6-3 1G).…”

“…To test the validity of this method for our N,-homocyclic system, we first applied it to the ground-state geometries and energies of c,t-(la) and c,c-triaziridine (lb)4), which had recently been calculated [2] by ab initio SCF MO. A comparison of the MNDO results with those of the ab initito calculations showed a qualitative agreement (see Chap.…”

“…The atom numbering is determined by the constitution (cf: IUPAC rules). When there is a choice of numbering then the one which leads to the lexicographically preferred descriptor (c,c < c,/ < t,c < t,t) is used (see [2], Footnote 3).…”

“…In the two t,c-examples 2a and 3a, 8 is about -55", which means that the nature of the substituents at N(2) and N(3) (H or alkyl) does not influence 0, probably because these substituents are both trans to the fonnyl group. When one of the substituents or both of them at N (2) and N(3) are cis to the formyl group, as in 2b, 3b, 2c, and 3c, 0 varies considerably. The cis-oriented H-atoms at these positions, as in 2b and 2c, appear to attract the formyl O-atom, since in 2b (H-N(2) cis to formyl) B = -32" meaning that the O-atom is closer to N(2) than in 2a (both H-N trans to formyl) and in 2c (both H-N cis to formyl) 0 = 15", i.e.…”