Nucleophilic displacement bimolecular

Bimolecular, nucleophilic-displacement reactions of sugar sulfonates have been reviewed in this Series.58,59 The value of these reactions in the preparation of deoxyhalo sugars has been emphasized by Hanessian.92... 

The results are better with bromides or iodides DMSO not only enhances bimolecular nucleophilic displacements at carbon atoms but also increases electrophilic substitution. 

Acid-induced mcemization and isomerization of chiral allylic alcohols. Bimolecular nucleophilic displacements in allylic compounds are known to proceed via the four possible pathways shown in Scheme 19. 

Bimolecular, nucleophilic-displacement reactions of sulfonic esters of carbohydrates have been reviewed.77,78... 

There has been great interest in recent years in bimolecular nucleophilic displacement reactions on organic compounds where the site of substitution is not carbon but oxygen, sulfur, or silicon. Since there is not room to discuss each of these reactions here, we shall briefly consider bimolecular nucleophilic displacements on sulfur as an example and refer the reader to recent reviews of displacement at oxygen55 and silicon.56... 

In its outer electronic shell divalent sulfur has two s and four p electrons, and it also has five empty 3d orbitals. A bimolecular nucleophilic displacement reaction on sulfur might then occur in a single step or an intermediate such as 7, in which the sulfur accepts the pair of electrons of the entering Lewis base into one of its... 

Bimolecular nucleophilic displacements on peroxide oxygen have been observed to occur. Would you expect the relative nucleophilicity of iodide to chloride in protic solvents to be (a) about the same toward peroxide O as toward sp3C (b) greater toward peroxide O than toward sp3C (c) smaller toward peroxide O than toward sp3C ... 

The study of gas-phase acid-induced nucleophilic displacement on 2,3-dihalobutanes has provided stereochemical evidence for the occurrence of cyclic chloronium and bromo-nium ions (X = Cl, Br), but not fluoronium ions17. Protonation or methylation of the neutral 2,3-dihalobutane by a suitable acid GA+ produces a halonium intermediate 2, which in the presence of water ultimately leads to the corresponding halohydrin neutral product (Scheme 4). Analysis of these neutral products indicated that the reaction proceeds with retention of configuration when X = Cl, Br and with inversion of configuration when X = F. The results were rationalized by the mechanisms sketched in Scheme 4, namely direct bimolecular nucleophilic displacement by H20 on 2 when X= F and intramolecular nucleophilic displacement to convert 2 into the cyclic halonium ion 3 (with inversion of configuation) followed by bimolecular nucleophilic displacement on 3 (with inversion of configuration) when X = Cl and Br. 

Attractive interactions may be viewed as incipient valence shell expansion and as the stages of bimolecular nucleophilic displacement reactions . Crystallographic data for the reaction pathways first described for cadmium complexes by Burgi reveal a correlation between the two X—Si and Si<-N distances in the linear... 

Epoxides undergo bimolecular nucleophilic displacement reactions with azide ion to produce azidoalcohols (Table 2). Azide ion preferentially attacks saturated unsymmetrical epoxides at the less substituted carbon atom in accordance with the normal pattern of polar... 

The general procedures previously outlined in this section for the formation of the carbon to azide bond have been widely employed in the steroid field, particularly as a stage in the stereospecific synthesis of aminosteroids. Bimolecular nucleophilic displacement reactions of sterols substituted with j -toluenesulphonyl, methanesulphonyl or halogeno groups etc. with azide ion proceeds with Walden Inversion and enables the stereospecific introduction of the azido group, which may then be reduced to an amino group. 

In the second case, the aquated metal ion hydrolyzes to give a coordinated reactive nucleophile. The bimolecular nucleophilic displacement can be represented as follows ... 

The increase in the rate of these three analogous bimolecular nucleophilic displacement reactions on transfer from methanol (a typical protic, hydrogen-bond donor type solvent) to DMF (a typical dipolar aprotic solvent) varies from a factor of 10 to 10 , being faster in the aprotic media. The medium has little effect on the CHgAT free energy, these molecules being slightly better solvated in DMF. This stabilisation is almost independent of X, The increase in rate clearly reflects the substantial destabilisation of the N on the transfer to DMF, modified by a small destabilisation of the transition state positive for Z = Cl... 

Bimolecular nucleophilic displacement reactions of sucrose sulfonates and deoxyhalides have been studied. Treatment of octa-O-(methylsulfonyl)sucrose (S) with sodium iodide in butcinone under reflux gave 6,6 -di-deoxy-6,6 -dideoxy-6,6 -diiodo-1, 2,3,3, 4,4 -hexa-0-(methylsulfonyl)sucrose (T) in 75% yield (26). The... 

Hydrolysis and condensation occur by bimolecular nucleophilic displacement reactions involving OH and Si-0 anions. For w > 4, the hydrolysis of all polymeric species is expected to be complete. Dissolution reactions provide a continual source of monomers. Because condensation occurs preferentially between weakly acidic species that tend to be protonated and strongly acidic species that are deprotonated, growth occurs primarily by reaction-limited monomer-cluster aggregation (equivalent to nucleation and growth), leading to compact, nonfractal structures. 

These trends indicate a close resemblance between the mechanism of oxidative addition here and bimolecular nucleophilic displacement from an aromatic carbon centre. Carbon-halogen bond breaking therefore seems implicated in the rate-determining step of the oxidative addition."... 

The previous sections have documented that the hydrolysis reaction of tetraalkoxy- and organoalkoxysilanes is influenced by sterlc and inductive effects and appears to be specific-acid-(H30 ) and specific-base-(OH ) catalyzed. The reaction order with respect to water and silicate is observed to be two and one, resulting in third- and second-order overall kinetics, respectively. Based on these factors, it is generally argued that hydrolysis proceeds by bimolecular nucleophilic displacement reactions (S y2-Si reactions) involving pentacoordinate intermediates or transition states... 

Above pH 7, hydrolysis and condensation occur by bimolecular nucleophilic displacement reactions (either S/.j2 -S, or S/v2 -Si) involving... 

---