Under suitable conditions, 2-bromobutane reacts with sodium hydroxide to produce a mixture of five products, A, B, C, D and E - AQA - A-Level Chemistry - Question 3 - 2022 - Paper 3

Stereoisomers are different compounds that have the same molecular formula and the same structural formula but differ in the spatial arrangement of atoms.

Name: But-2-ene (or 2-butene depending on context)

Explanation: A does not exhibit stereoisomerism because it does not have a C=C double bond capable of existing in cis/trans forms due to the lack of different substituents on the double-bonded carbons.

1. The hydroxide ion acts as a base and removes a proton from a hydrogen atom adjacent to the bromine-bearing carbon (deprotonation).

2. This results in the formation of a double bond between the carbon atoms, while the bromide ion is expelled as a leaving group.

Names: B is cis-2-butene, C is trans-2-butene.

Explanation: The origin of stereoisomerism in B and C arises from the restricted rotation around the C=C double bond, which leads to different spatial arrangements of the substituents around the double bond.

Enantiomers D and E can be represented in 3D as follows:

• D: (S)-2-butanol

• E: (R)-2-butanol

(Visual representation would typically include rotated structures showing stereochemistry.)

Order: 1-iodobutane > 1-bromobutane > 1-chlorobutane.

Explanation: The order of hydrolysis rates is based on the reactivity of the halogen; iodine is the best leaving group, followed by bromine and then chlorine. Therefore, 1-iodobutane hydrolyzes fastest, leading to the quickest formation of the precipitate.