The molecular structure of allenes and ketenes. XIV—semi‐empirical descriptions of 13C chemical shifts of ketene imines and deduced from the effects of isoelectronic substitutions in allenes

An essentially algebraic model for semi‐empirical calculations of 13C chemical shicts of ketene imines and ketenes is presented which utilizes geometrical and non‐geometrical aspects of symmetry. In particular, emphasizing isoelectronic substitution as a generalized symmetry principle, it is shown that approximation functions for the description of 13C chemical shifts of ketene imines and ketenes can be deduced from those used for the allenes, and that the parameters which are necessary for the calculations of the carbon resonances of the heterocumulenes are simply related to those used for the allenes. A comparison between calculated and experimental 13C chemical shifts of complex ketene imines and ketenes demonstrates the relevance of the suggested model.