The distance between 4-H and adjacent H on the substitutional benzene ring in benzo[c]carbazole was calculated in terms of molecular structure parameters. The result showed that the distance is shorter than the sum of van der Vaals’ radii of two hydrogen atoms. This means that there is a steric hinderance between them. This effect will make the bond angle stretch and the bond length extend, or cause the molecule to distort, thus making benzo[c]carbazoles become unstable in thermodynamics. On the contrary there is no such effect for benzo[a]car...
