Chemistry of the n-Bond

A. H. M. Renfrew, Reactive dyes for Textile Fibres the Chemistry of Activated n-bonds as Reactive Groups and Miscellaneous Topics, Society of Dyers and Colourists, Bradford, 1999. 

For many years the occurrence of double and triple bonds such as discussed above for silicon and phosphorus was equally rare among other nonmetals, leading to the conclusion that only C=C, C =N, C 0. NsN. etc. were stable multiple bonds. This, of course, was taken as challenge and much svnthetic work was directed at the problem. None of the multiple bonds between heavier nonmetals is as strong as those between the 2p elements. Some typical estimates of the strength of the n bond (cf. to H,C CH3 as a "standard" from organic chemistry) arc (values in kJ mol-1). ... 

M. N. Mruzek, in The Chemistry of the Double-bonded Functional Groups (Ed. S. Patai), Wiley, Chichester, 1989, pp. 53-79. 

The (s-cA-butadiene) Group 4 metallocenes adopt a a2,7i-type structure. The actual strength of the n-bonding component and, hence, the metallacyclopentene character of the complexes depends very much on the substitution pattern of the diene ligand6 and it is also strongly influenced by the nature of the bent metallocene unit. These various influences were recently analyzed for some ansa-metallocene/ 1,3-diene combinations by means of computational chemistry,83,84 and the results were compared with the dynamic features (AGfw of the ring-flip inversion process, solid... 

We have seen that the % bonding orbital is distinctly different in shape and symmetry from the a bond. There is another important feature of the n bond that is of far-reaching consequence, particularly in organic and coordination chemistry. 

The potential between the reactive atoms that we used is one that has been used before in studies of many-atom systems,eind which we have examined to insure that it recovers the essential chemical facts that are known to us. (However, one surely does not yet know all that there is to know about the high energy chemistry of the N/O system.) The potential has a functional form that allows for a weakening of a bond between a pair of atoms when one or more other reactive atoms are nearby. In other words, the potential has many-atom terms. It also Includes a long reinge van der Waals attraction which describes the packing in the cold cluster. For more details, see Ref. 95. 

A study of the structural properties of primary n-alkylammonium haUdes enabled us to evaluate the relative importance of intermolecular forces of the two types as the polar ends of the layers form strong hydrogen-bonded networks that dominate the packing on crystallization. Here we illustrate trends in the crystal chemistry of the n-alkylammonium halides, and the investigative methods, using as examples n-octadecylammonium chloride, CigH37NH Cl , and their related bromides and iodides... 

As a natural extension of the chemistry of [n]cyclophanes, remarkable advances have been achieved in the chemistry of [n]cyclophanes of condensed benzenoid aromatics. Because of the diversity of the n bond orders and large HOMO/LUMO electron densities, condensed aromatics are more sensitive to strain imposed by the short bridge than the corresponding benzologue. From this point of view, the naphthalene and anthracene analogues of [6]paracyc-lophane were synthesized and their geometries and reactivities were investigated. Particularly noteworthy is that they exhibit extraordinary reactivities. 

The solubility of 4-7 is somewhat limited in solvents of low coordinating ability as a consequence of their hydrogen bonding properties which leads to the formation of head-to-tail dimers in the solid state (37). Accordingly we have also explored the chemistry of the N,N-dimethyl ligand 8. Under the usu synthetic conditions a 67 % yield of oxidative addition product 9 was crystallized and spectroscopic data are in accord with the proposed structure (equation 11). 

It has been known for more than a century that hydrocarbons containing double bonds are more reactive than their counterparts that do not contain double bonds. Alkenes are, in general, more reactive than alkanes. We call electrons in double bonds 71 electrons and those in the much less reactive C—C or CH bonds Huckel theory, we assume that the chemistry of unsaturated hydrocarbons is so dominated by the chemistry of their double bonds that we may separate the Schroedinger equation yet again, into an equation for potential energy. We now have an equation of the same fomi as Eq. (6-8), but one in which the Hamiltonian for all elections is replaced by the Hamiltonian for Ji electrons only... 

The chemistry of the disilenes (disilaethenes) has developed very rapidly since the discovery of stable compounds. It was an obvious challenge to explore also the possibility of a n-coordination of disilenes to transition metals. According to the Dewar-Chatt-Duncason bonding model, a high stability for a disilene complex should result. 

An indication of growing interdisciplinary interest in the field is illustrated in a review on new perspectives in surface chemistry and catalysis by Roberts (.160), who discussed the interaction of N2 with iron surfaces. In so doing, he referred to the Fe (N2) , matrix Mdssbauer work of Barrett and Montano (7), which showed that molecular nitrogen only bonds to iron when the latter is present as a dimer. As the chemisorption studies (161) indicated that N2 is absorbed on singleatom sites, Roberts suggested (160), of the matrix data (7), "if this is correct, then our assignment of the N(ls) peak at 405 eV to end-on chemisorbed N2 will require further investigation. Other reviews that consider matrix-isolation techniques for chemisorption simulation are collected in footnote a. 

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