Thermal and photochemical behaviour, structure and bonding of the stereoisomers of 6,7,8,9,14a,14b-hexahydrodipyrido[1,2-a:2′,1′-c][1,4]diazocine

The meso and (±) isomers of the title compound have been prepared by reduction of 1,1′-(butane-1,4-diyl)dipyridinium dibromide with sodium amalgam. The meso form converts thermally into the (±) form, which reverts photochemically into the meso form through the diradical intermediate. The diradical generated by photolysis was characterized by EPR and absorption spectroscopy. MNDO calculations indicate that the energetically most favourable meso and (±) conformers possess an extremely long C–C single bond of ca. 1.60 A at the position joining the two 1,2-dihydropyridine rings, the latter being lower in energy than the former by 5.7 kcal mol–1. The available experimental facts are reasonably accounted for by the theoretical results.

[1]  T. Muramatsu,et al.  The Thermal and Photochemical Behaviors of the Cyclomers of Ethylenebis- and Trimethylenebis(pyridinyl) Diradicals , 1990 .

[2]  T. Muramatsu,et al.  The Thermal and Photochemical Behavior of the Cyclomers Derived from 1,1′-(1,3-Propanediyl)bis(pyridinyl) Diradicals , 1990 .

[3]  T. Muramatsu,et al.  Photosensitive cyclomer formation of 1,1'-(1,2-ethanediyl)bis(pyridinyl) diradical and its derivatives , 1989 .

[4]  T. Muramatsu,et al.  The 1,1'-ethylenebis[4-(methoxycarbonyl)pyridinyl] diradical and its photosensitive cyclomers , 1987 .

[5]  P. March,et al.  Conformational studies of annulated 2,2'-bipyridinium salts , 1987 .

[6]  Y. Ikegami.  Kinetic ESR and CIDEP studies on the monomer-dimer equilibrium systems of pyridinyl radicals , 1987 .

[7]  E. Kosower.  Stable Pyridinyl Radicals , 1983, Preparative Organic Chemistry.

[8]  M. Hatano,et al.  CNDO and INDO Calculations of the Magnetic Circular Dichroism of Several Purine Derivatives , 1980 .

[9]  Walter Thiel,et al.  Ground States of Molecules. 39. MNDO Results for Molecules Containing Hydrogen, Carbon, Nitrogen, and Oxygen , 1977 .

[10]  Walter Thiel,et al.  Ground States of Molecules. 38. The MNDO Method. Approximations and Parameters , 1977 .

[11]  H. Schlegel,et al.  Long bonds and through-bond coupling , 1976 .

[12]  R. Gleiter.  Effects of Through-Bond Interaction , 1974 .

[13]  H. Zeldes,et al.  Paramagnetic resonance study of liquids during photolysis. XIV. Pyridine, pyrazine, pyrimidine, and pyridazine , 1972 .

[14]  Michael J. S. Dewar,et al.  The molecular orbital theory of organic chemistry , 1969 .

[15]  R. Hoffmann,et al.  Benzynes, dehydroconjugated molecules, and the interaction of orbitals separated by a number of intervening sigma bonds , 1968 .

[16]  J. Pople,et al.  Approximate Self‐Consistent Molecular‐Orbital Theory. V. Intermediate Neglect of Differential Overlap , 1967 .

[17]  M. Itoh,et al.  Charge-transfer complexes between substituted pyridyl radicals , 1967 .

[18]  E. J. Poziomek,et al.  The Isolation and Distillation of the Stable Free Radical, 1-Ethyl-4-carbomethoxypyridinyl , 1963 .