DFT-GIAO-NBO and 13C NMR study of the delta-syn-axial effect in 2,4-disubstituted adamantanes.
Six groups of diastereomeric 2,4-disubstituted adamantanes were studied with DFT-GIAO-NBO (natural orbital analysis) methods. The calculated (13)C chemical shifts reproduce well the experimental data. It was found that among all diastereomers, those bearing substituents in delta-syn-axial positions showed the largest overall deshielding, i.e. the sum of all (13)C chemical shifts [Sigmadelta((13)C)] was the greatest and also had the highest delocalization contribution to the molecular energy evaluated with NBO. The higher delocalization energy is proposed to be the origin of the deshielding delta-syn-axial effect.
Mikhova
B
B
Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria. bozhana@orgchm.bas.bg
Stamboliyska
B
B
Koch
A
A
Duddeck
H
H
Kleinpeter
E
E