Inclusion of hydrogen p orbitals in the semiempirical calculation of NMR parameters. I. Influence on the FPT INDO spin–spin coupling constants

Hydrogen 2p orbitals have been introduced into the basis set to calculate the Fermi contact term of spin–spin coupling constants using the FPT INDO method. Different coupling constants show different sensitivity to these hydrogen polarization functions. Some improvements are found for molecules containing N or F. Calculations of proton-proton geminal coupling constants give more negative results than those of FPT INDO , yielding a better agreement with experimental values. The π-transmission mechanism is notably exaggerated.     

Dependence of geminal1H−1H and31P−1H spin-spin coupling constants on the specific intramolecular C−H...X interaction

Participation of the proton in a specific intramolecular C−H...X (X=N, 0) interaction leads to an increase in its geminal¹H−¹H and¹H−³¹P spin-spin coupling constants (SSCC). According toab initio calculations carried out in the 6–31G^** basis set, the observed effect is mainly due to the change in the diamagnetic spin-orbital contribution to SSCC. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 306–309, February, 1997.     

Diazapolycyclic compounds. XXVII. On the selective hydrogenation of benzo[g]phthalazine-1,4-dione and 5-methoxybenzo[g]phthalazine-1,4-dione adducts

A number of diazapolycyclic structures obtained by cycloaddition reaction of benzo[g]phthalazine-1,4-dione with several 1,3-dienes have been catalytically hydrogenated on palladium over charcoal. In a first step the double bond formed in the cycloaddition was reduced, except in the case of tetrasubstitution. The use of longer reaction times led to the selective reduction of the terminal aromatic rings, although the presence of the 5-methoxy substituent favored tetrahydropyridazine ring opening and prevented aromatic ring reduction. The stereochemical features of new compounds obtained are commented on the basis of X-ray and nmr data.