preview

Alkyl Halides

Decent Essays

In this lab, the experimenters will determine how the structure of an alkyl halide (i.e. methyl, primary, secondary, or tertiary), steric effects, nature of a leaving group, and solvent polarity affect the relative rates of SN1 and SN2 reactions. In addition, comparing the rates of reactions under varying concentrations of alkyl halides and nucleophiles will help determine the rate laws for both types of nucleophilic substitution reactions. During SN2 reactions, a good nucleophile, like iodide, will displace the leaving group on an alkyl halide in a single step that results in an inversion of configuration. Methyl, primary, and some secondary halides undergo this bimolecular substitution reaction. Minimal steric effects combined with a good leaving group and a polar, aprotic solvent …show more content…

The more stable the resulting carbocation, the quicker this step occurs. After this rate-limiting step, rapid reaction with a weak nucleophile (e.g. ethanol) attacking from either side of the carbocation completes the substitution reaction. A racemic mixture forms with a slight favoring of the inverted molecule because of ion pair formation. A good leaving group capable of delocalizing a negative charge aids in the formation of the initial carbocation. Additionally, polar, protic solvents capable of solvating and stabilizing a carbocation support the SN1 mechanism. Tertiary alkyl halides provide the ideal substrate for the formation of a stable tertiary carbocation that favors the SN1 mechanisms. When testing the factors affecting the SN2 reaction below, the experimenters will achieve the fastest reaction when using a primary alkyl halide with minimal branching and the best leaving group (i.e. 1-bromobutane). Varying the concentrations of the alkyl halide or nucleophile while keeping the other constant will change the rate of reaction for the SN2 reaction. The fastest SN1 reaction will occur for the tertiary alkyl halide with the strongest leaving group reacted in pure

Get Access