Atoms asymmetrical

In this paper, asymmetric carbon atoms are considered only in paraffins and substituted paraffins, and the following definition will be retained (cf. Sec. 36(b)) A carbon atom is called asymmetric if the four bonded radicals arc pairwise structurally different. (Thus, it is not sufficient to require that the four radicals are not stereoisomers in order to declare a carbon atom asymmetric. One could envisage other, possibly useful, definitions.)... 

Tetragonal co-ordination with 2 chelating pn ligands and S-bonded NCS groups Centrosymmetric dimer. Each Cu surrounded by 7 atoms. Asymmetric bidentate NO 3 co-ordination Both have exactly trans planar co-ordination... 

A stereogenic carbon atom (chiral center, chiral atom, asymmetric atom) is bound to four unlike groups and thus generates chirality. Note that a molecule may possess a molecular chirality without having a stereogenic center. 

Moreover, Complexes 118 and 119 react with mercury(II) chloride to give the IrIIi-Irl derivatives 135 and 136, resulting from oxidative addition of HgCl2 to one metal center. A related complex, [Rh2(/i-pz)2(/r-HgCl)Cl(CO)2(PPh3)2], which exhibits a mercury atom asymmetrically bridging the two rhodium centers, was previously characterized by X-ray diffraction (116). 

Tile structure of 8 is illustrated in Fig. 3. The calcium atom asymmetrically caps the open hexagonal face of the nido-1ligand... 

In September 1874 van t Hoff announced his theory of what he called the "asymmetric carbon atom" (a misleading phrase, since it is not the carbon atom itself but rather its chemical environment that van t Hoff conceived as asymmetric). Since this history has recently been well treated, I will provide only a brief account. First, van t Hoff drew attention to an empirical rule. He demonstrated that evidence known at that time was consistent with the thesis that whenever four different atoms or radicals are attached to any single carbon atom through its four valence units, a new kind of isomerism presents itself, one that is associated empirically with optical activity. He called any such carbon atom "asymmetric." In particular, there was no recognized case of an optically active organic compound that was known not to have an asymmetric carbon atom by this definition, somewhere in its structural formula. 

Strategy Recall the condition for chirality. Is the central C atom asymmetric that is, does it have four different atoms or different groups attached to it ... 

Montanari and co-workers have prepared the first example of an optically active aziridine where the asymmetry is solely due to a tervalent, nonbridgehead nitrogen atom. Asymmetric chlorination of 2,2-diphenylaziridine with either (lR,2/ )-(—)-isobomyl hypochlorite or the (-f)-W-chloro-sulphoximine (651) gave reasonable yields of optically active 7V-chloro-2,2-diphenylaziridine. 

Atom-nonlinear molecule complexes are of two basic types atom-symmetric top and atom-asymmetric top. Several such complexes have been studied through their pure rotational spectra, but high-resolution infrared spectra, involving excitation of Van der Waals bending and stretching modes, are only just starting to become available. There has also been some theoretical work on the photodissociation spectra of such systems, but this has concentrated on the rates of photodissociation processes rather than on the energy level patterns. 

CSA calculations can be performed of rotational excitation cross sections for atom-asymmetric top collisions quite easily at low collision energies. To date, the only application of the CSA to an atom-polyatomic molecule vibrational-rotational problem has been to He+CO2(01 0,j 00 0,j )[27] and some of these calculations are described in Section HI. 

The most often encountered type of radical observed by LMR is the three-atomic asymmetric-top radical, such as NH2, PH2, HCO, HO2, etc., Hund s case (b). In this case, the Hamiltonian [1] is used. Without... 

Asymmetric hydroamination has served as an important strategy for the synthesis of pyrrolidine and piperidine derivatives. Moreover, it has been found to be useful for the synthesis of other five- and six-membered heterocyclic compounds having more than one hetero atom. Asymmetric hydroamination and diastereoselective hydroamination have been found to be extremely useful for the synthesis of natural products and pharmaceutical agents. It is important to note that diastereoselective hydroamination has been... 

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