Sn mechanism

The anionic moiety can substitute chlorines in PVC by an Sn mechanism [Eq. (31)]. The reaction can also take place by an Sn mechanism. This would involve the formation of a cationic center on the polymer backbone... 

Naqvi and Joseph [139] studied the kinetics of acet-oxylation of PVC using 18-crown-6 to solubilize KOAc in organic solvents under mild reaction conditions. They concluded that the substitution of chlorines in PVC by acetoxy groups proceeded by an Sn mechanism. 

In the case of allyl peroxides (12 X= CH2, A=CH2, BO),1 1 1 intramolecular homolytic substitution on the 0-0 bond gives an epoxy end group as shown in Scheme 6.18 (1,3-Sn/ mechanism). The peroxides 52-59 are thermally stable under the conditions used to determine their chain transfer activity (Table 6.10). The transfer constants are more than two orders of magnitude higher than those for dialkyi peroxides such as di-f-butyl peroxide (Q=0.00023-0.0013) or di-isopropyl peroxide (C =0.0003) which are believed to give chain transfer by direct attack on the 0-0 bond.49 This is circumstantial evidence in favor of the addition-fragmentation mechanism. 

Cooper(I) carboxylates give esters with primary (including neopentyl without rearrangement), secondary, and tertiary alkyl, allylic, and vinylic halides. A simple Sn mechanism is obviously precluded in this case. Vinylic halides can be converted to vinylic acetates by treatment with sodium acetate if palladium(II) chloride is present. ... 

Fluorination with retention of configuration (such as in 327) has often been attributed to steric crowding on the opposite side of the hydroxyl group, hindering the back side of the fluoride ion for Sn2 attack. However, a possible Sn/ mechanism by loss of an OSp2NEt2 fragment to give a car-bonium cation, followed by front-side attack of fluoride ion, should be... 

Miller, J. and Yeung, H.W. (1967) Sn Mechanism In Aromatic Compounds.35. Comparative Reactivity Of Pentachloro-fluorobenzene Hexafluorobenzene And Fluorobenzene. Australian Journal of Chemistry, 20(2), 379-381. 

The influence of the donicity on the rate of the reverse reaction k21 is considerably smaller, probably since the ratedetermining step is the dissociation of a chloride ion (SN mechanism). 

In acid solution it is assumed that the aquapenta-cyano ion reacts to form an intermediate, and that the intermediate may react with water, or may be picked up by a scavenger such as azide ion to form products. It is also assumed that the complex, which has a pK of 9.8 is in equilibrium with ROH, the predominant species in akaline solution. The decision that we had to make was whether the decrease in rate occurred because ROH was a completely inert species, or whether ROH also underwent an Svl mechanism as well as this. It was our conclusion that the evidence favored two parallel Sn mechanisms. 

Ethers are produced from phenol by the Williamson method via an SN mechanism. 

The latter method via cyclization and subsequent ring contraction at one or several centres in most cases makes use of cyclizations to sulfides [3]. These cyclizations follow Sn mechanisms and are easy to carry out giving high yields of the cyclic sulfides, which are easily isolable [6, 7], For the ring contraction step, in this case a desulfurization step, a variety of methods is at hand ... 

Arakawa T, Timasheff SN. Mechanism of protein salting in and salting out by divalent cation salts balance between hydration and salt binding. Biochem 1984 23 5912-5923. 

It can be shown that aromatic nitrogen mustards (compounds containing an aromatic ring) usually alkylate via the SN, mechanism. 

The observed order of ease of rearrangement of the acetylenic phosphites, tertiary > secondary > primary, appears to be consistent with the postulated SN/ mechanism. 

Predict the products of the following reactions, all of which proceed by an Sn mechanism. Write a balanced equation for each reaction. 

Properties.—Studies of the mechanical properties of (SN) crystals using compression stress-strain techniques under ambient conditions, show plastic behaviour resembling that of a highly anisotropic metal, and Young s modulii, parallel and perpendicular to the chain axis, were found to be 21 and 1.4 GPa, respectively. Crystals of (SN) , mechanically deformed and examined using transmission electron microscopy, show the formation of a number of kink bands perpendicular to the chain axis, and a model has been formulated to enable prediction to be made of kink angles. ... 

The reaction of alkenyl epoxides with organometallic species (lithium, magnesium, copper, and boron) affords allylic alcohols, following an Sn and/or Sn mechanism. These processes can accommodate only little organic functionality and exhibit low regio- and/or stereoselectivity. Under smooth conditions, C—C bond formation proceeds by nucleophilic alkylation of vinyl epoxides in the presence of catalytic amounts of zerovalent palladium. Regio- and stereoselectivity can be achieved via the formation of a Tr-allylpal-ladium complex. Trost and Molander and Tsuji and co-workers simultaneously reported the first studies in 1981. Since then, numerous papers have dealt with this subject. Essentially, after chelation and oxidative addition of the palladium onto the vinyl epoxide, the zwitterionic 7r-allylpalladium complex deprotonates the nucleophile, which can in principle attack either carbon 2 (proximal attack) or 4 (distal attack) (Scheme 1). 

In both cases the formal oxidation state of the metal is increased (+11). Whereas in the OA mechanism the total valence number is also increased, it is maintained in the SN mechanism. For a given reaction the mechanism involved will essentially depend on the catalyst s nature (Mn, Co, Fe... 

Consider a nucleophilic substitution reaction in a complex with coordination number six (CN = 6) octahedral (Oh) substrate MX5Y occurring via SN mechanism. 

According to SN mechanism, the first step involves the loss of the leaving group Y. This breaking of the M—Y bond results into formation of a five-coordinated (trigonal bipyramidal/square pyramidal) intermediate. This step is slow and hence a rate determining step. 

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