Displacements on carbon

The reaction therefore involves nucleophilic displacement on carbon passing through the transition state indicated otherwise expressed, the reaction involves nucleophUic di.splacement in the conjugate acid R—OH2 in which the displaced group is OHj" " ... 

The alkoxy phosphonium intermediate is formed by a reaction that does not break the C-0 bond and the second step proceeds by back-side displacement on carbon, so the stereochemistry of the overall process is inversion. 

Whether this unsatisfactory state of affairs is a consequence of a borderline situation as encountered in displacements on carbon, or the result of a penta-covalent addition intermediate, remains to be demonstrated. 

The orbital requirements for radical attack on any polyene are given in Table 6. If H3, HC2 and Cl8 (see Walsh diagram, Fig. 2) can be taken as models, then three-center transition states will be linear. If, however, cyclic transition states can be formed, HMO theory indicates a preference for them (Fig. 1). Unfortunately, attempted radical displacements have not been observed, simply because the radicals take other reaction paths (Pryor, 1966). The transition states may have been linear, but for abstraction from rather than displacement on carbon (Bujake et al., 1961). If the radical and molecule generated in these cases remain in... 

Similar equations have been proposed by Swain et al. to correlate all nucleophilic displacements on carbon. However, the number of parameters has grown to four, and the usefulness of such a system of bookkeeping is open to question. ... 

Phosphoryl and nucleotidyl transfer reactions are nucleophilic displacements on phosphorus 3—6), and like analogous displacements on carbon (7) or on metal ions (5), have been found to take place by mechanisms varying between two extreme or limiting cases 1. In the dissociative or SnI mechanism the initial departure of the leaving nucleophile, yields the planar triply coordinate metaphosphate anion as a reactive chemical intermediate (3, 8), which then combines with the entering ligand on either face of the metaphosphate plane 2. In the associative... 

X on the electrophilic carbon atom (Figure 5). Since carbon is more electronegative than aluminum reaction would proceed by a), but due to the stcric hindrance (since branched alkyl groups are used) decay of the complex proceeds by b). The alkoxide may be produced in situ from aluminum trichloride and ether. This reaction proceeds in a similar way through the Lewis adduct, followed by nucleophilic displacement on carbon (Figure 6). 

It is also conceivable that reduction occurs by methide displacement on carbon to yield hydroperoxide, which is subsequently reduced to alcohol (9, 10) and methanol. We cannot at present distinguish... 

The electrophilic substitution reactions involving imidoyl halides are centered around the displacement on carbon-hydrogen bonds. For example,... 

Further examples (see Vol. 2, p. 281) of 5u2 displacement on carbon in bis-triflamides [e.g. Br" -I- PhCH2 N(S02 CFs)2 - PhCHaBr + "N(802 CFs)2] are to hand. Similar C—N cleavage occurs readily in acyl w o-triflates (e.g. MeCO--NPh-802-CFs from MeCOCl -I- PhNH-SOaCFs + EtsN), which therefore function... 

In the work from my own laboratory over the last ten years or so we have used a combination of experimental measurements on selected reactants and model calculations relating to a-deu-terium effects on the rates of solvolytic nucleophilic displacement on carbon to try to correlate all known results on such reactions in terms of Scheme I. 

Mechanistic studies concerned with nucleophilic displacement on carbon... 

Nucleophilic displacement on carbon. Write an equation for the reaction of ethyl bromide with each of the following nucleophiles (a) HS (b) CHjO (c) H- (d) rCHj- [Pg.507]

Displacement on carbon. Account for the fact that (CHslgCBr reacts with very dilute OH in CH3OH to give (CHalsCOCHs and not (CHa)sCOH. 

Radical displacement on carbon is extremely rare, excluding examples in which a strained ring is cleaved. One case that has been claimed involves the formation of cyclopropane from the 3-iodo-1-propyl radical (eq. 22). The mechanism in eq. 22 has been criticized (52) on the basis of the high strain generated in the... 

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