Modeling NMR Parameters by DFT Methods as an Aid to the Conformational Analysis of cis-Fused 7a(8a)-Methyl Octa(hexa)hydrocyclopenta[d][1,3]oxazines and [3,1]benzoxazines

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• 作者：Petri Tä ; htinen ; Alessandro Bagno ; Karel D. Klika ; and Kalevi Pihlaja
• 刊名：Journal of the American Chemical Society
• 出版年：2003
• 出版时间：April 16, 2003
• 年：2003
• 卷：125
• 期：15
• 页码：4609 - 4618
• 全文大小：287K
• 年卷期：v.125,no.15(April 16, 2003)
• ISSN：1520-5126

文摘

The energies of the preferred conformations of four 7a-methyl octa(or hexa)hydrocyclopenta[d][1,3]oxazines, five 8a-methyl octa(or hexa)hydro[3,1]benzoxazines, and 8a-methyl hexahydro[1,3]benzoxazinone, all cis-fused, were investigated by DFT methods. Following geometry optimization at theB3LYP/6-31G(d,p) level, both the proton chemical shifts and the vicinal coupling constants between H-4aand the H-4 and H-5 protons were calculated at the B3LYP/cc-pVTZ level and compared to the previouslyexperimentally measured values. The agreement between the calculated and the experimental chemicalshifts was found to be good. Similarly, the agreement between the calculated and the experimental vicinalcoupling constants was also found to be good, thus providing a methodology for determining theconformational equilibria of such systems that is comparable in many respects to experimental approachessuch as variable-temperature NMR or to the use of model coupling constant values, when available, fromanalogous compounds.