Organic Chemistry

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Practice

1.

The following reaction exhibits first order rate in each reactant. What happens to the rate of the when:

 a) The concentration of 2-bromobutane is doubled and [EtONa] remains the same?
b) The concentration of 2-bromobutane is tripled and [EtONa] is halved?

Check your answers

 

Sodium ethoxide is a strong base and its reaction with a secondary alkyl halide will mainly yield an elimination product through E2 mechanism which can also be seen from the reaction equation. The rate of the E2 reaction depends both on the substrate and the base and therefore the following changes will be observed:

a) The rate doubles
b) The rate increases 1.5 times (3 x 1/2 = 3/2)

2.

Identify the β hydrogens and draw the curved arrow mechanism for each of the following E2 reactions.

Check your answers

 

The substrate in each reaction has two types of ß-hydrogens; the one(s) that yield, in an elimination reaction, the Zaitsev product and the one(s) that yield the Hofmann product. These hydrogens are marked in blue and red colors respectively.

For this exercise, you need to identify the correct ß-hydrogen that participated in the reaction based on the position of the double bond in the product.

More material and practice about the Zaitsev and Hofman (regiochemistry of E2 reaction) products can be found here.

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