Monday, December 2, 2013

Problem Solution

From Sapling: What product(s) are expected in the ethoxide-promoted beta-elimination reaction of 2-bromo 2,3 dimethylbutane? (omit ions, salts, and ethanol).

The first step is to draw the starting material:

Next it is important to note the type of reaction which is elimination with ethoxide (a strong base and good nucleophile) which classifies it as an E2 reaction. The expected product is an alkene.

Once the reaction type has been noted and an idea of the type of product being generated has been thought through, it is important to classify the alpha-carbon and beta carbons from which elimination can occur. This starting material has two beta carbons from which elimination can occur, thus two products can be formed: one major and one minor (see the picture below). Finally the mechanism of the E2 reaction must be considered, it is concerted: the leaving group leaves and a double bond is formed in the same step and the product alkene is generated.


The reaction obeys Zaitsev's rule with the major product being, 2,3 dimethyl 2-butene (the more substituted alkene).


  1. Nice animations/pictures! Definitely makes it easy to understand! I like how you broke it down step by step, elimination reactions can be confusing sometimes. Especially in regards to figuring out which Beta Carbons work the best.

  2. Great post! your diagrams are really effective; they made the reaction visual and easy to follow. This solution was a nice refresher on key points of E2 reactions, such as alpha/beta carbons, and the preferential formation of the more stable product according to Zaitsez`s rule.