Abstract: The calculation formulae of the bent bond and strain characteristics in 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 unsaturated 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 bent bonds in strained organic molecules is less than that of acyclic hydrocarbons. The bond length increases with the increase of ring size and the decrease of bent angles. The bond length of C-C bonds in polyhedroang 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°,whatever the bent angle(0-32°) and bond angles(60-140°)are greater or small. The real bond angles of high strained organic molecules are much more greatly deviated from the tetrahedral angle 109.5°than those of less strained or strainless molecules. However, the real bond angles H-C-Hor H-C-C of three-membered rings have a tendency towards the angle 120°rather than 109.5°, It can be concluded that the deviaton(△β) of bent bond angles from the tetrahedral angles 109.5°can be used to evaluate the molecular strain and stability.

Key words: Strain, Behavior of bent bonds, Hellmann-Feynman force