Multibond

Wender, P. Miller, B.L. (1993) Toward the Ideal Synthesis Connectivity Analysis and Multibond-Forming Processes. In Organic Synthesis Theory and Applications, Vol. 2 (ed. T. Hudlicky), pp. 27-65. JAl Press, Greenwich, CT. 

Yamaguchi, C. Kawashima, N., Combination of improved multibondic method and the Wang-Landau method, Phys. Rev. E. 2002, 65, 056710... 

HMBC Heteronuclear multiple-bond correlation spectroscopy To elucidate structure of organic molecules To establish long-range (i.e., multibond) heteronuclear coupling... 

Probably an attempt should be made to replicate the one-bond drive results reported in this paper by the multibond drive technique (108,120). 

Phosphorus, Arsenic, Antimony and Bismuth Ligands 14.5.3.3 Miscellaneous phosphorus-element multibond % complexes... 

Examples of intramolecular transformations209 include dienone-a,(3-unsaturated ester cyclizations, e.g. (275— 276),209a>b and ester-a, p - unsaturated ester annulations, e.g. (277—>278 Scheme 91).209c Pertinent to the success of these multibond formation protocols is the selective use of the initiating carbanion (or enolates), the counter cation and the initial acceptor. 

For adsorbed H2 (and D2) Krasser and Renouprez (52) found several extremely weak Raman bands in the range 600-2100 cm"] which were assigned to linear NiH species (2028 and 1999 cm" ) and multibonded NixH species at 1600 and 950 cnrl and again no studies of the spectral changes with respect to reactivity of the NiH species with other molecules were carried out. 

The continuing accumulation of experimental material made it, however, still more apparent that the above criteria, both kinetic and stereochemical [61-64], cannot be regarded as absolute [65], since there are probably both concerted reactions which are forbidden as well as nonconcerted ones which are allowed. An example of the first type of reaction is some 2 + 2 retro-cycloadditions on sterically strained systems [62,66] the second type of processes is then represented by the so-called multibond reactions [67]. This, of course, stimulates to formulate a new and more universal criterion of concertedness as well as a deeper understanding of the very concept of concertedness. 

Table 3. Calculated values of second order similarity indices gRP, gRI and gIP for several selected pericyclic (multibond) reactions...

In the nineteenth century, when the picture was still rather crude, chemists attempted to prepare compounds with a true Si-Si double bond. An oversimplified analogy was relied on at that time carbon-carbon multibonds are formed during the decomposition of carbides like calcium carbide, therefore compounds with Si-Si multiple bonds ought to be formed in the decomposition of calcium silicide. 

However, I think Ken was at his creative best fifteen years ago when we coauthored an invited review on Synchronicity in Multibond Reactions for Annual Reviews of Physical Chemistry. This review was written to refute Michael Dewar s assertion in a JACS paper that synchronous multibond reactions are normally prohibited . The review provided a rare occasion when Ken and I could each write on this subject without having to respond to a three-page, single-spaced, report from an anonymous Referee, which usually wound up by claiming that, if we weren t ignorant, then we must be scientifically dishonest in asserting that multibond reactions actually could be synchronous. 

One of the outstanding characteristics of enzymes is that they are able to function as enantioselective catalysts and carry out chemical reactions with absolute stereospecificity. As a result, most natural compounds are produced as optically pure enantiomers. The enantioselectivity of enzymatic catalysis is ascribed to the formation of a multibonded complex of substrate and reagent within the active center of the chiral enzyme molecule. The creation of chemical systems capable of serving as enantioselective catalysts represents one of the central and most challenging problems of modern chemistry. In the last decades. 

A number of miscellaneous methods which involve multibond formation are included here for completeness in spite of the fact that their synthetic utilities do not appear to be great. A reaction which closely resembles the a-halogenokeione-amide method is the cyclization of an a-chloro-a-phenylthioketone (prepared from the diazoketone) with ammonia and a carboxylic acid. It has been used to prepare 2-ethyl-4-methyl-5-phenylthioimidazole in 32% yield [68]. 

Activation parameters for monoperoxycarbonates (Table 111) indicate a one-bond homolysis reaction. In comparison to di-t-butylperoxyoxalate where multibond homolysis occurs, the rate coefficient for di-f-butyl monoperoxycarbonate is 10 times slower at 45 °C . The rate of decomposition of di-t-butyl diperoxy-... 

Figure 8(a) demonstrates the dependence of the normalized CO intensities at pure Pt (0co = O-48) and Pt-Fe (saturated coverage, 0co = O.55) on the electrode potential. The difference of the electronic structure between pure Pt and Pt skin layer on the CO-tolerant alloys, mentioned above, is reflected in the infrared spectra of chemisorbed CO, i.e., the multibonded CO, which might require the contribution of the 5d electron, was hardly found on the skin layer [27-30]. This is in contrast to the... 

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