Compiling toxicological facts from animal testings for numerous N-nitrosamines together with formally derived carbocations or carbenium-ions results in a clear view on these metabolites from N-nitrosamines whether or not they can initiate carcinogenesis in animal organisms. The widely accepted metabolism of N-nitrosamines to carbenium-ions is also demonstrated. However, to understand the carcinogenic potential of one carbenium-ion and the inability of others we calculated the heat of formation (Delta H-ct) for carbenium-ions from easily available thermodynamical data. The calculation of energies of formation (Delta E(ct)) is demonstrated, hypothesis on carcinogenicity/non-carcinogenicity are formulated. Products and compounds are demonstrated.