Calculations of geometries of organic molecules using the CNDO/2 method—I : Empirical correlations between observed and calculated bond lengths in simple acyclics, strained cycloalkenes and some polycyclic molecules

Abstract

It is shown that calculations of CC and CH bond lengths in hydrocarbons using the CNDO/2 semi-empirical MO method exhibit systematic deviations from the observed values. An empirical correlation relating the observed and calculated bond lengths with the number of substituents attached to the bond may be devised. This correlation is capable of providing theoretical bond lengths within 0·008 Å of the experimental for a wide range of simple acyclic molecules. Furthermore, calculations of molecular geometries for some strained cycloalkenes and also some larger molecules, e.g., naphthalene, biphenylene and azulene, are similarly found to be in good agreement with experiment.