An ab initio study on selected models of 1,2- cis- and 1,2- trans-cyclic carbamates of glucopyranosyl amine

• Published in: Journal of molecular structure. Theochem 1997-05, Vol.395, p.41-52
• Main Authors: Paizs, B., Pintér, I., Kovács, J., Viviani, W., Marsura, A., Friant-Michel, P., Csizmadia, I.G.
• Format: Article
• Language: English
• Subjects: Ab initio; Amino-cyclohexanol; Amino-tetrahydorpyrane; Configurational stability; Conformational stability; Cyclic carbamate; Glycopyranosyl amine
• ISSN: 0166-1280; 1872-7999
• DOI: 10.1016/S0166-1280(96)04539-3

Total energies of various conformations of trans- and cis-isomers of 2-amino-cyclohexanol ( 5) and those of 2-amino-3-hydroxy-tetrahydropyrane ( 6) as well as those of 2,3-cyclic carbamates of 2-amino-3-hydroxy-tetrahydropyrane ( 7) were computed at HF/6-31G and HF/6-31G ∗∗ level of theory for modelling the energy differences between trans- and cis-1,2-cyclic carbamates of gluco- and xylopyranosyl amine ( 1, 2 and 3, 4, respectively). In the case of the chair forms of both 5 and 6, the trans isomers were found to be more stable than the cis ones. The stability of the different structures was also governed by the internal hydrogen bonds involving NH 2 and OH groups, as well as the ring oxygen atom. In the case of 7, the formation of the oxazolinone ring results in decreasing the total energy of the cis isomer with respect to the trans compound. Using appropriate isodesmic reaction equations, stabilization energies were calculated for all of the model structures of 5–7, as well as for the transition from cyclohexane to tetrahydropyrane. The energy values indicated that the introduction of the ring oxygen causes stabilization in all cases.