Cluster compounds, chiral

Cluster compounds, chiral, 27 191 molybdenum-sulfur, 27 47 transition metal, 27 182... 

Now consider the symmetry point group G (or, more precisely, the framework group [70]) of the above ML coordination compound or -vertex cluster compound. This group has G operations of which R are proper rotations so that G / R = 2 if the compound is achiral and G / R = 1 if the compound is chiral (i.e., has no improper rotations). The distinct permutations of the n sites in the coordination compound or cluster are divided into / / right cosets [71] which represent the permutational isomers since the permutations corresponding to the i proper rotations of a given isomer do not change the isomer but merely rotate it in space. This leads naturally to the concept of isomer count, I, namely... 

Isopropyl group (Section 2 13) The group (CH3)2CH— Isotactic polymer (Section 7 15) A stereoregular polymer in which the substituent at each successive chirality center is on the same side of the zigzag carbon chain Isotopic cluster (Section 13 22) In mass spectrometry a group of peaks that differ in m/z because they incorporate differ ent isotopes of their component elements lUPAC nomenclature (Section 2 11) The most widely used method of naming organic compounds It uses a set of rules proposed and periodically revised by the International Union of Pure and Applied Chemistry... 

The problem that we noted above with clusters appears also in chemical enumeration when we consider compounds formed by attaching radicals which may be chiral or achiral to a frame which is achiral. In this case, too, Polya s Theorem cannot be used, but the problem can be solved by the appropriate use of Burnside s Lemma. It is also amenable to the methods of Redfield, as shown in [DavRSl] and [LloE85]. 

Charge density-NMR chemical shift correlation in organic ions, 11, 125 Charge distribution and charge separation in radical rearrangement reactions, 38, 111 Chemically induced dynamic nuclear spin polarization and its applications, 10, 53 Chemiluminesance of organic compounds, 18, 187 Chiral clusters in the gas phase, 39, 147... 

Dirhodium(II) carboxylate catalysts have been used extensively for the catalysis of carbene insertions. In many cases, impressive selectivities have been achieved (19-21). In an effort to find selective catalysts for carbenoid insertions, Moody screened a series of dirhodium(II) carboxylate catalysts for their ability to catalyze carbenoid Si-H insertion (22). The authors surveyed the commercially available carboxylic acids, -10,000 of which are chiral. The members of this group that contained functionality that is incompatible to the reaction were culled out. The remaining chiral carboxylic acids (-2000 compounds) were then grouped into 80 different clusters. There is no discussion presented for the criteria used in the grouping of the acids. A representative acid from each cluster was then chosen for... 

Related phosphine-substituted derivatives were also obtained, and the chirality of the clusters demonstrated by the NMR spectra of the compounds (246). Molecules of this type have obvious utility in establishing the potential intermediacy of the polynuclear adduct in a catalytic reaction by the formation of optically active products. 

A wide range of thermochemical properties can be measured, including not only proton affinity or gas-phase basicity, but also electron affinity, ionization energy, gas-phase acidity and cation affinity Entropy changes upon attachment of an ion to a molecule are also accessible and provide information on both the nature of the bonding and fragmentation mechanisms in cluster ions, especially in biological compounds. Thermochemical determinations by the kinetic method also provide very useful structural information e.g., two-electron three-center bond has been observed in the gas phase by means of the kinetic method. " In the last years, the kinetic method has been also applied to characterize chiral ions in the gas phase. 

The chiral discrimination in the self-association of chiral l,3a,4,6a-tetrahydroi-midazo[4,5-d]imidazoles 3 has been studied using density functional theory methods [37], (Scheme 3.20). Clusters from dimers to heptamers have been considered. The heterochiral dimers (RR SS or SS RR) are more stable than the homochiral ones (RR RR or SS SS) with energy differences up to 17.5 kJ mol-1. Besides, in larger clusters, the presence of two adjacent homochiral molecules imposes an energetic penalty when compared to alternated chiral systems (RR SS RR SS...). The differences in interaction energy within the dimers of the different derivatives have been analyzed based on the atomic energy partition carried out within the AIM framework. The mechanism of proton transfer in the homo- and heterochiral dimers shows large transition-state barriers, except in those cases where a third additional molecule is involved in the transfer. The optical rotatory power of several clusters of the parent compound has been calculated and rationalized based on the number of homochiral interactions and the number of monomers of each enantiomer within the complexes. 

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