Leaving group reactions

Another reaction mechanism explaining the observed enhancement of A 0bs values with increasing [amine]o values in S vAr reactions is the dimer mechanism 276, which involves the self-association of the amines277-279 and which (in some cases) may be considered overlapped with mechanism of Scheme 14. A reaction pathway for dimer mechanism is shown in Scheme 17. Considering the zwitterionic intermediate 114 it is possible to have a catalysis in removing the proton and the leaving group (reaction pathway indicated by fc3). 

As we showed previously in this chapter, silicon easily expands its valence shell to become a penta-coordinated species. Therefore, it is expected that an intramolecular transfer of organosilicon group from X to Y may occur via a radical mechanism, provided that the R substituents on the silicon atom are not good leaving groups (Reaction 6.20). 

Alkyl azides are conveniently prepared from the reaction of alkali metal azides with an alkyl halide, tosylate, mesylate, nitrate ester or any other alkyl derivative containing a good leaving group. Reactions usually work well for primary and secondary alkyl substrates and are best conducted in polar aprotic solvents like DMF and DMSO. The synthesis and chemistry of azido compounds is the subject of a functional group series. ... 

H and FT are poor leaving groups, reaction irreversible and get protonation... 

Aryloxy groups have also been used as leaving groups. Reaction of 1-chloro- and l-methanesulfonyl[l,4]benzo-dioxino[2,3-r/]pyridazine 164 and 4-chloro[l,4]benzodioxino[2,3-Hpyridazine with NaOMe afforded ring-opened and cyclized pyridazines (Scheme 40). Their reaction with amines afforded 1-substituted [l,4]benzodioxino[2,3-rf]pyr-idazines 165, 4-substituted [l,4]benzodioxino[2,3-f]pyridazines 166, and/or 2-hydroxyphenoxypyridazines 167 (Scheme 41) <2004H(63)591>. 

A two-step process converts an OH group into OPOCI2, a good leaving group reaction of the OH group with POCI3 followed by removal of a proton. 

FIG. 2. The imcraction of ACh, CM, and OP compounds with the active. site serine of AChE and BuChE. Reaction I represents the formation of a stable Michaelis complex and the beginning of the nucleophilic attack of the serine. Reaction 2 represents the acylation of the active site serine, coupled with the relca.se of the fir.st reaction product or leaving group. Reaction 3 begins the nucleophilic attack of a hydroxyl ion, which leads to the regeneration of active enzyme (reaction 4). 

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