Attack, adjacent remote

M s-, outer-sphere reduction by Co(CN) -. Remote attack. Adjacent attack. J. H. ... 

At the second stage of chlorine substitution in the tetramers there is a greater statistical probability for the incoming nucleophile to attack the phosphorus adjacent to =P(C1)(NHR), viz. P4 or P8, rather than the remote phosphorus, viz. P6 (Fig. 9). However, this statistical effect is countered by the electron releasing effect of the substituent already present on P2, which tends to deactivate P2 as well as P4 and P8 towards further nucleophilic substitution. It is observed that reactive amines such as dimethylamine (94) or ethylamine (95) react with N4P4C18 and... 

More subtle factors that might affect k will be the sites structures, their relative orientation and the nature of the intervening medium. That these are important is obvious if one examines the data for the two copper proteins plastocyanin and azurin. Despite very similar separation of the redox sites and the driving force (Table 5.12), the electron transfer rate constant within plastocyanin is very much the lesser (it may be zero). See Prob. 16. In striking contrast, small oxidants are able to attach to surface patches on plastocyanin which are more favorably disposed with respect to electron transfer to and from the Cu, which is about 14 A distant. It can be assessed that internal electron transfer rate constants are =30s for Co(phen)3+, >5 x 10 s for Ru(NH3)jimid and 3.0 x 10 s for Ru(bpy)3 , Refs. 119 and 129. In the last case the excited state Ru(bpy)3 is believed to bind about 10-12 A from the Cu center. Electron transfer occurs both from this remote site as well as by attack of Ru(bpy)j+ adjacent to the Cu site. At high protein concentration, electron transfer occurs solely through the remote pathway. 

If the bridging ligand contains only one atom (e.g.. Cl ). both metal atoms of the complex must be bound to it. However. If the bridging ligand contains more than one atom (e.g.. SCN ). the two metal atoms may or may not be bound to the same bridging-ligand atom (see Problem 13.30). Hie two conditions are called adjacent and remote attack, respectively. A remote attack may lead to both linkage isomers ... 

The expedient and regioselective metalation of unprotected biphenyl-2-, -3-, and -4-carboxylic acids has been reported.59 Unprotected biphenyl-2-carboxylic acid has been cleanly metalated with. sex-butyllithium at the position adjacent to the carboxylate and can then be subjected to site-selective electrophilic substitution (Scheme 8). The remote C(2 )-position has been attacked by the superbasic mixture of n-BuLi and t-BuOK (LICKOR) in THF or benzene. The resulting dianion cyclizes to give the fluorenone skeleton. The mechanism of the metalation of homologous compounds, 2-(pyridin-3-yl)benzoic acid derivatives, with strong bases has also been discussed.60... 

The presence of hydroxyl groups, both adjacent and remote from the epoxide group, have been found to control the regio- and stereo-specificity of the tetracyanoethylene-catalysed methanolysis of cyclohexane epoxides.44 Because the nucleophilic attack occurs at the carbon remote from the hydroxyl group with inversion of configuration, it was suggested the hydroxyl group participates in the reaction. 

The carbon-silicon bond has two important effects on the adjacent alkenc. The presence of a high-energy filled CT orbital of the correct symmetry to interact with the n system produces an alkene that is more reactive with electrophiles, due to the higher-energy HOMO, and the same ff orbital stabilizes the carbocation if attack occurs at the remote end of the alkene. This lowers the transition state for electrophilic addition and makes allyl silanes much more reactive than isolated alkenes. 

The severance of the Cr—S bond to form the stable HgSCN" species requires no further comment, and the isomerism is assumed to proceed by either of the routes just described. The stable [(HaOjgCr— NCS—Hg] + species has been separately characterized in solution (39). More recently the attack of Cr on [CofNELajaNCS] " has been shown to be remote only, whereas the attack on the linkage isomer is both adjacent and remote (677). The reduction of FeNCS by Cr in the presence of NCS leads to kinetic and spectroscopic evidence for [Cr(H20)4(NCS)(SCN)]. The analysis of the results is made more difficult by the uncertainty concerning the ratio of geometric isomers present and the mechanism by which this species is formed (129). 

N=C=S—OlOHj) ] are produced. (1 has been postulated ihat both remote and adjacent attacks are involved in the formation of these products. Draw bridging intermediates consisicni with this view for the formation of both producls. ... 

Nucleophilic additions to cyclic carbonyl compounds differ greatly from those of acyclic systems. In acyclic systems, only the configuration at an adjacent (1,2-asymmetric induction) or nea y center (remote asymmetric induction) is usually considered in predicting the outcome of nucleophilic attack. In cyclic systems, the conformation of the entire molecule (which is in part determined by the individual substituents) must be considered when predicting the mode of nucleophilic attack. Furthermore, a number of other factors such as torsional and electronic effects also play a role in the stereochemical course of additions to cyclic substrates. The relative importance of all of these effects (as well as others) has been the subject of considerable debate in the literature, and has not as yet been adequately resolved. ... 

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