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The crystal structure of RU60358, C20H21NO3, has been determined using X-raydiffraction to establish the configuration and stereochemistry of the molecule around theC15-C16 triple bond. The compound crystallises in the orthorhombic space group P212121, a= 7.7575, b = 11.3182, c = 21.3529Ã¥, V = 1874.80Ã¥3 and Z = 4. The structure has beenrefined to a final R = 0.068 for the observed structure factors with I ≥ 3à (I). The refinedstructure was found to be significantly non planar. A comparative study, using the ab initiocalculations of the structure at B3LYP/6-31G** levels of theory, shows good geometricalagreement with the X-ray diffraction data. Standard deviations between the calculated andexperimental bond values have been shown to be 0.01 Ã¥ and 0.5° for bond angles.Vibrational wavenumbers were obtained from a normal mode analysis using the ab initiocalculations.