Relations among Bond Order, Force Constant and Bond Length for the C–C and the C–N Bond in Conjugated Molecules

A general equation correlating bond orders with bond lengths of bonds between any particular pair of atoms in the conjugated systems are proposed. To test this equation applications have been made for C–C and C–N bonds. Because of the scarcity of the calculated values of bond orders for C–N bonds in the literature, bond orders of several molecules containing C–N bonds have been calculated, It is shown that the order-length relation is in good agreement with experiments. A theoretical, although approximate, equation correlating bond lengths with force constants has also been proposed and applied to C–C and C–N bonds. From these relations the length and the stretching force constant of C–N double bond are estimated to be 1.295 Å and 9.1×105 dynes/cm, respectively, the former being in agreement with the value calculated from the covalent radii given by Pauling.