Nucleophilic Substitution and Elimination

What does the term "nucleophilic substitution" imply? • A nucleophile is an the electron rich species that will react with an electron poor species • A substitution implies that one group replaces another. Nucleophilic substitution reactions occur when an electron rich species, the nucleophile, reacts at an electrophilic saturated C atom attached to an electronegative group (important), the leaving group, that can be displaced as shown by the general scheme: The electrophilic C can be recognised by looking for the polar σ bond due to the presence of an electronegative substituent (esp. Nucleophilic substitution reactions are an important class of reactions that allow the interconversion of functional groups. Of particular importance are the reactions of alkyl halides (R-X) and alcohols (R-OH) For alcohols, the range of substitution reactions possible can be increased by utilising the tosylates (ROTs), an alternative method of converting the-OH to a better leaving group. SN2 mechanism SN2 indicates a substitution, nucleophilic, bimolecularreaction,described by the expression rate = k [Nu][R-LG]. This implies that the rate determining step involves an interaction between these two species, the nucleophile and the organic substrate. This pathway is a concerted process (single step) as shown by the following reaction coordinate diagrams, where there is simultaneous attack of the nucleophile and displacement of the leaving group. The nucleophile attacks at the carbon with the partial positive charge as a result of the polar σ bond to the electronegative atoms in the leaving group.