The Dehydration Of An Alcohol

1372 Words Nov 18th, 2016 6 Pages
In the dehydration of an alcohol to an alkene, an alcohol is protonated into a weak base and a good leaving group and is able to undergo elimination. An elimination reaction allows for an organic compound to be turned into an alkene product. However, there are two mechanisms for elimination: E2 and E1. The reaction conditions determine which mechanism is more likely to occur. An E2 mechanism exhibits second order kinetics and is a one-step concerted mechanism, where a bond is broken at the same time that a PI bond is formed. Because it is bimolecular, the substrate and the base are in the rate law and affect the rate of the reaction. Thus, an E2 mechanism prefers a strong base and prefers to be in a polar aprotic solution in order for the rate of the reaction to proceed faster. The opposite is an E1 mechanism that exhibits first order kinetics, but is a stepwise reaction in which the timing of bond breaking and bond making is different. The bond between the leaving group and the carbon breaks, and the departure of the leaving group leaves a carbocation intermediate. An E1 reaction prefers a weak or mild base, as opposed to a strong base, because only the substrate is in the rate law. However, it prefers a polar protic solvent because the partial positive charges of the hydrogen atoms solvates the carbocation, and provides more electron density, an overall stabilizing effect.

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