THEORETICAL-STUDIES ON BENT BOND, STRAIN AND BONDING BEHAVIOR OF STRAINED ORGANIC-MOLECULES

The calculation formulae of the bent bond and strain characteristics i n any strained organic molecules are proposed. The relationship among structure, strain, stability and reactivity on 38 typical hydrocarbons -cyclic, bicyclic hydrocarbons, propellanes, polyhedranes and some uns aturated hydrocarbons has been revealed: (a) the C-C bond of strained organic molecules with three- or four-membered rings are much greater than those with five- or six-membered rings, (b) the bond length of be nt bonds in strained organic molecules is Less than that of acyclic hy drocarbons. The bond length increases with the increase of ring size a nd the decrease of bent angles. The bond length of C-C bonds in polyhe droang increases with the increase of the size of polyhedral framework ; (c) the real bond angles (defined as equation 7 in the paper) have a tendency towards tetrahedral angle 109. 5 degrees, whatever the bent angle(0-32 degrees) and bond angles(60-140 degrees) are greater or sma ll. The real bond angles of high strained organic molecules are much m ore greatly deviated from the tetrahedral angle 109. 5 degrees than th ose of less strained or strainless molecules. However, the real bond a ngles H-C-H or H-C-C of three-membered rings have a tendency towards t he angle 120 degrees rather than 109. 5 degrees. It can be concluded t hat the deviaton <Delta beta> of bent bond angles from the tetrahedral angles 109. 5 degrees can be used to evaluate the molecular strain an d stability.