Nucleophilic Substition Reactions

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ewis base, the faster the nucleophile will attack the substrate. For the SN2 reaction to occur, the use of a polar aprotic solvent should be used. Ideally, the substrate should remain depronated or else a front side attack of the nucleophile may take place. This is why the non-polar solvent is used. The temperature of the mechanism is low (Carey 322). Once the environme!
nt is established, the reaction proceeds as follows:
H H H H
Nu + H C X Nu-----C------X Nu C H + X
H H H
The rate-determining step is when the nucleophile is partially bonded to the carbon atom, while the leaving group is partially being pushed off. This intermediate is called a pentacoordinate (309). The substitution from the opposite side causes inversion of the product to invert from its starting configuration of dextrorotary (+) or levorotary (-) to its opposite enantiomer. Walden inversion is the name of this process. The product produced is one hundred percent of the inversion of the reactant (308).
In the substitution unimolecular reaction (SN1), the rate is also based on the substrate's structure, the nucleophile’s basicity, and the reaction conditions. The mechanism is unimolecular and it is a two-step process. The first-order rate law is described as Rate = k [substrate] (Smith 394). The concentration of the substrate is the sole component in the rate law. This is from the slow step of the substrate’s ionization to form the carbocation. This must occur first. Because the formation of the carbocation, caused by the removal of the leaving group, requires less energy in tertiary and secondary structures, SN1 reactions never occur with methyl or primary substrates (393). A good leaving group is a...