Microwave spectra and structure of the amine group in 3-aminopyridine and 4-aminopyridine. Ab initio molecular orbital calculations of the structure of the amine group in the aminopyridines

Abstract

Microwave spectra of the ground and first excited vibrational states of the normal and amine deuterated species of 3-aminopyridine and 4aminopyridine have been assigned and the structure of the amine group has been determined in these two molecules. The structure of the amine group in the aminopyridines has been derived from ab initio molecular orbital calculations using single determinant molecular orbital wave functions constructed from standard minimal basis sets of contracted Gaussian orbitals. The experimental and theoretical results are found to be in broad agreement with each other.

From the nonplanarity of the amino group to the structural nonrigidity of the molecule: A post-Hartree-Fock ab initio study of 2-aminoimidazole

“…In our opinion, a considerably deeper understanding of this phenomenon might be achieved if one took into account all possible pathways of Ž interconversion the anisotropic internal rotation of the amino group around the exocyclic C᎐N bond . y and the plane inversion of the CNH fragment 2 of CNH y fragment in amines. To our knowledge, 2 there are only two articles in which this question has been partially investigated regarding the ani-w x line molecule 28, 29 .…”

“…y and the plane inversion of the CNH fragment 2 of CNH y fragment in amines. To our knowledge, 2 there are only two articles in which this question has been partially investigated regarding the ani-w x line molecule 28, 29 . The inversion dynamics of w x the amino group have been investigated in 28 , and the barriers for inversion and the internal rotation of the amino group in a quasi-classical w x approximation have been calculated 29 .…”

“…nonequivalent syn-and anti-amino group rotations and one plane inversion of the CNH fragment. All three transition states 2 are characterized by C point group molecus lar symmetry. All pathways of the intercon-version are accompanied by mutual structural relaxation of the CNH fragment and 2 the rest of the molecule.…”

Structure ofN,N-dimethyl-1,4-phenylenediamine

“…The amino and the dimethylamino groups are pyramidal forms, and the lone-pair orbitals on the N atoms in these groups are oriented on the same side of the phenyl-ring plane in the respective molecules. The planarity of the amino and the dimethylamino groups is conveniently defined by tp, where ~0 is the angle between the bisector of the angle Me--N--Me or H--N--H and the extension of the bond C(ipso)-N (Christen, Norbury, Lister & Palmieri, 1975). The values of ~0(dimethylamino) and ~0(amino) are respectively 41.7 and 48.2 ° for molecule A, and 42.2 and 45.0 ° for molecule B.…”

Structure of 4-dimethylaminopyridine N-oxide dihydrate

“…Torsion angles C(3)-C(4)-N(7)--C(9)=-1.3 (3) and C(5)-C(4)-N(7)-C(8)=-0.7(3) ° show about 1 ° rotation of the dimethylamino group around the bond C(4)-N(7). The planarity of the dimethylamino group is conveniently defined with (0 presented by Christen, Norbury, Lister & Palmieri (1975), where ~0 is the angle between the bisector of the angle C(8)--N(7)--C(9) and the extension of the bond C(4)--N(7). The value of ~0 is 0.3 o; the conformation of the dimethylamino group is completely planar.…”