Crystal data

Rhodium(II) compounds have become the premier choice in catalytic transformation of a-diazo compounds to induce cyclopropanation, aliphatic carbon-hydrogen bond insertion, heteroatom hydrogen bond insertion, aromatic substitution, and ylide formation. 

The behavior of bimetalated rhodium(II) compounds with head-to-tail configuration (type Vila) in catalytic transformation of a-diazo compounds has been also studiedJ Results have confirmed that by changing the carboxylate groups and the substituents on the metalated and non-metalated rings of the phosphine the activity and the regio and chemoselectivity of these compounds can be substantially modified. 

Catalyst Ref. Yield (%) Relative ratio tertiary C-H insertion secondary C-H insertion 

Competing C-H insertion reactions mediated by this type of catalyst have been also studied. In this type of reaction the complex with triphenylphosphine and acetate was shown to be both reactive and very selective, yielding only the tertiary C-H insertion product (Table 2). When a catalyst with the less basic phosphine PPh2(CeF5) was used, this slightly reduced both reactivity and selectivity. More electrophilic catalysts with heptafluorobutyrates as carboxylates were less selective. 

We also tested the reactivity and selectivity of mono metalated complexes (Type V). These catalysts, although reactive, were in general less selective than bimetal-ated compounds with head-to-tail configuration. Finally, preliminary studies of reactivity of doubly metalated compounds with the head-to-head configuration (Type Vllb) showed that these compounds are not promising catalysts for C-H insertion reactions. 

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The Empirical Conformational Energy Program for Peptides, ECEPP [63, 64], is one of the first empirical interatomic potentials whose derivation is based both on gas-phase and X-ray crystal data [65], It was developed in 1975 and updated in 1983 and 1992. The actual distribution (dated May, 2000) can be downloaded without charge for academic use. 

J. D. H. Doimay and H. M. Ondik, Crystal Data Determinative Tables, 3rd ed, U.S. Department of Commerce, National Bureau of Standards Joiut Committee on Powder Diffraction Standards, Washiagton, D.C., 1972, pp. 0-23, 0-73, 0-97, 0-106. 

As a result of having two chiral centers, four stereoisomers of ascorbic acid are possible (Table 1) (Fig. 2). Besides L-ascorbic acid (Activity = 1), only D-araboascorbic acid (erythorbic acid (9)) shows vitamin C activity (Activity = 0.025-0.05). The L-ascorbic acid stmcture (1) in solution and the soHd state are almost identical. Ascorbic acid crystallizes in the space group P2 with four molecules in the unit cell. The crystal data are summarized in Table 2. 

Currently, there are about 197,500 entries in the National Institute of Standards and Technology (NIST) Crystal Data File. An exhaustive search takes about one minute. Unit cell parameters are very definitive. Usually only one or a few hits are found and the appropriate Hterature reference(s) are Hsted. If no hits are found, the stmcture has not been previously reported. 

Indexings and Lattice Parameter Determination. From a powder pattern of a single component it is possible to determine the indices of many reflections. From this information and the 20-values for the reflections, it is possible to determine the unit cell parameters. As with single crystals this information can then be used to identify the material by searching the NIST Crystal Data File (see "SmaU Molecule Single Stmcture Determination" above). 

Pyrano[3,2-g]benzoxazine, dihydrosynthesis, 3, 714 Pyranobenzoxazines synthesis, 6, 190 Pyranobenzoxazoles mass spectra, 3, 615 Pyrano[2,3-a]carbazoles synthesis, 4, 235 Pyrano[2,3- 6]carbazoles synthesis, 4, 235 Pyrano[3,2-a]carbazoles synthesis, 4, 235 Pyranochromones synthesis, 3, 821 Pyranochromones, dihydrosynthesis, 3, 81 817 Pyranocoumarins crystal data, 3, 623 mass spectra, 3, 610 Pyranodipyranones synthesis, 3, 794 Pyrano[3,2-6]indol-4-ones synthesis, 4, 302 Pyran-2-ol, dihydrodehydration, 3, 762 Pyran-2-ol, 3-methyltetrahydro-synthesis, 3, 775 Pyran-2-ol, tetrahydro-6-substituted synthesis, 3, 775 Pyran-4-ol, tetrahydro-IR spectra, 3, 594 Raman spectra, 3, 594 Pyranols, tetrahydro-bond lengths, 3, 621 synthesis, 3, 777... 

This list is not exhaustive, partieular systems often require other speeifie data to be eolleeted. Sueh data ean take eonsiderable time to eolleet experimentally unless effieient experimentation is employed. Crystallization data are published in divers sourees ineluding textbooks and journals, many of whieh have been referred to throughout the text and are listed at the end of this book. Published... 

The sphere radii were deduced from Slater s (1965) table based on crystal data. The basic molecular HF-Xa equations were originally derived on the basis that the spheres did not overlap (Schwarz and Connolly, 1971). But the equations remain valid when the spheres are allowed to overlap, provided that each sphere does not contain more than one nucleus and that none of the nuclei lie outside the outer sphere. A 10% overlap seems to be normal practice, and our results are given in Table 12.2. 

Symmetry of the anion in the crystal. Data in parentheses give the approximate (non-crystallographic) symmetry Solvent molecule(s) in the crystal structure... 

Table 6. Crystal data and phase sequences of mesogenic trans,trans-4,4 -n-m-dia kyl-il,l -bicyclohexyl)-4 -carbonitriles (CCNnm)...

Table 13. Crystal data and phase sequences of mesogenic carboxylate compounds ...

In the last few years the crystal structures of some mesogenic azine compounds have been determined [2, 133-136]. The general chemical structure of the azines is shown in Fig. 24. The crystal data and the phase sequences of the investigated mesogenic azines are presented in Table 15. 

This data was taken from "Crystal Data"- Am. Crystallographic Assoc. Monograph - W. Nowacki- Ed. (1967)... 

It is important to point out that in the discussion that follows the term "Na coverage" is used this does not imply that the promoter is thought to be present in the form of chemisorbed metallic sodium as it would be in vacuum. The reactive gas atmosphere is expected to lead to the formation of surface compounds of Na, and single crystal data indicate... 

The upper panel in Fig. 5.17 compares the experimentally determined PVDOS for the oriented array of Fe(TPP)(NO) crystals with that for Fe(TPP)(NO) powder. The crystal data is recorded with the incident X-ray beam 6° above the mean porphyrin plane. Since the NIS measurement is only sensitive to Fe motion along a probe direction, the spectral contribution of modes with predominantly in-plane Fe motion are enhanced, and the contribution of out-of-plane modes is suppressed in the oriented crystal data. 

Table 17.2 Crystal data of rutile, CaCl2 and marcasite...

The crystal data compared to expected values assuming no distortions are summarized in Table 18.1. Inspection of the atomic coordinates reveals that the distortions of the packing of spheres are only marginal. As expected, the greatest deviations are observed for the molecular compounds PI3 and NMe3. 

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