Wendy J. Dixon, Frank Hibbert and Richard E. Overill
Theoretical calculations of minimum energy structures and thermodynamic terms using SCF theory with thermodynamic and solvation corrections have been made of the cyclisation of 1-amino-8-(acetylamino)naphthalene to give 2-methylperimidine with the liberation of water and of the related reaction of 1-hydroxy-8-(acetylamino)naphthalene to 2-methylnaphtho[1,8-d,e][1,3]oxazine. The calculations predict that in the gas phase the former reaction is strongly thermodynamically favourable (ΔG = –37.9 kJ mol–1, ΔH = –0.6 kJ mol–1 and TΔS = +37.3 kJ mol–1 at 298.2 K) whereas the latter is much less favourable (ΔG = –2.0 kJ mol–1, ΔH = +31.1 kJ mol–1 and TΔS = +33.1 kJ mol–1 at 298.2 K). The results are in qualitative agreement with experimental observations for the reactions in solution. Reasons for the different behaviour of the two reactions are discussed.