Refinement of the population and radial dependence of the spherical atomic valence shell is introduced in a general crystallographic least-squares program. The radial dependence is described by an expansioncontraction parameter K, which, in the nine data sets tested, indicates contraction of positively and expansion of negatively charged atoms in agreement with theoretical concepts such as those incorporated in Slater's analytical rules for atomic orbitals. H atoms appear more contracted than concluded previously on the basis of a comparison of X-ray and neutron thermal parameters of sucrose. An average value of 1.40 for the radial contraction of H is used in structures for which no neutron thermal parameters are available. The resuiting net charges are used to calculate X-ray molecular dipole moments whose magnitude and direction are in good agreement with theoretical and other experimental results, though some differences may be expected because of matrix effects. Net molecular charges in the one-dimensional conductor TTF-TCNQ agree with results obtained earlier by direct integration of the charge density over the molecular volume. A charge transfer from Si to V in the superconducting alloy V3Si is also in agreement with earlier results.
477 generated by the present method, since their precursors are readily accessible from o-t~lualdehyde.~ In a parallel line of experiments, cyclopentanone moiety 13 was prepared in an almost stereoisomerically pure form, starting from 2-methyl-2-cyclopentenone (12) by modifications of the reported method. l c i d , fThe assembly of the bromide 13 with 3 was carried out by adding 13 to the benzylic carbanion 5 at -75 "C to room temperature, which had been generated in situ from 3, according to the procedure described above. In the assembly of the bromide 13 with 4, HMPA was added to the carbanion 6, generated in situ prior to the alkylation. Deketalization of the coupling products 7 and 8 afforded the crucial precursors 14 and 15" as stereoisomeric mixtures [14, 2:l;" 15, 1:2 (the former is less polar)] in 94% and 95% yields, respectively, after preparative TLC [14: TLC on silica gel, Rf0.60 (6:4 AcOEt-C6H6); 15: TLC on silica gel, Rr 0.59 and 0.38 (6:4 AcOEt-CqH6),]. The final intramolecular cyclization of 14 and 15 via the corresponding o-quinodimethanes was exemplified with the estrone synthesis. To an acetonitrile solution (20 mL) of a diastereo-14, X = OMe; R = H 15, X = H; R = CH, 1-16, X = OMe; R = H 1 7 , X = H ; R = C H , R 18, X = OMe; R = H 2 , X = H ; R = C H ,
A new cembranoid diterpene was isolated from the soft coral Cladiella krempfi from Minicoy Island (India), and its structure was established by X-ray crystallography to be sclerophytin F methyl ether {2] with the R absolute configuration at all six epimeric centers, assuming a configuration similar to that of sclerophytin C. Compound 2 may be an artifact of the isolation process.Novel sterols, prostaglandins, and especially cembranoid diterpenes have been reported from alcyonarian soft corals and gorgonians of the phylum Coelenterata. Natural products produced
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