Nucleophile characteristics

The description of the carbon-oxygen double bond is analogous, but in addition to the cr-bonds there are unshared pairs of electrons on oxygen so that two excited states are possible, n-n and n-n. For n-n excitation the resultant half-vacant orbital on oxygen should possess electrophilic reactivity, and the electron rich -system should have nucleophilic characteristics. 62>... 

In addition to the above prescriptions, many other quantities such as solution phase ionization potentials (IPs) [15], nuclear magnetic resonance (NMR) chemical shifts and IR absorption frequencies [16-18], charge decompositions [19], lowest unoccupied molecular orbital (LUMO) energies [20-23], IPs [24], redox potentials [25], high-performance liquid chromatography (HPLC) [26], solid-state syntheses [27], Ke values [28], isoelectrophilic windows [29], and the harmonic oscillator models of the aromaticity (HOMA) index [30], have been proposed in the literature to understand the electrophilic and nucleophilic characteristics of chemical systems. 

Abstract The use of iV-heterocychc carbenes as catalysts for organic transformations has received increased attention in the past 10 years. A discussion of catalyst development and nucleophilic characteristics precedes a description of recent advancements and new reactions using A-heterocyclic carbenes in catalysis. 

Many of these inhibitory elements are either electrophiles or nucleophiles characteristic of one type of protease. 

The nitrogen atom of the nitrile possesses some nucleophilic characteristics. When a carbocation is generated by protonation of an alkene, it may be discharged by a nitrile. This reaction, known as the Ritter reaction, leads to the formation of amides (Scheme 3.92). 

A molecule like ethene, which has a carbon/carbon double bond, has a centre of high electron density in the ji bond. Thus, nucleophiles characteristically have a high electron density. Would they be attracted to a positive or negative centre ... 

An analysis of crystal structures showed that if one of the sulfur atoms acts as an electrophile, it approaches the other which thus has nucleophilic characteristics [20]. Thus the mutual arrangement of the two nonbonded XSY groups is such that one sulfur atom (Sj, the electrophile) approaches another sulfur atom (S2, the nucleophile) in the X2S2Y2 plane in such a way that S2 lies in a direction perpendicular to the XjSjYj plane (Fig. 6). 

In (A), the reaction will predominate on the left-hand side. Exceptions appear to be olefins with strong electron-releasing substituents that confer thermodynamic stability to the newly formed cation, -CH2-CHR . This either results from a suitable charge delocalization over the 7r-electron system or from the presence of a heteroatom. Accordingly, only those olefins that possess relatively strong nucleophilic characteristics can be polymerized by stable carbon cations. Such olefins are alkyl vinyl ethers, A -vinyl carbazole, p-methoxystyrene, indene, and vinylnaphthalenes. Styrene and cf-methylstyrene, however, will not polymerize, because they are less reactive. 

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