AQA A level Chem 3.1 Introduction to Organic Chemistry

Define the term stereoisomers. (2)

(Different molecules/compounds with the) same (molecular and) structural formula (1)

Different spatial arrangement of atoms (1)

Under suitable conditions, 2-bromobutane reacts with sodium hydroxide to

produce a mixture of five products, A, B, C, D and E.

Products A, B and C are alkenes.

A is a structural isomer of B and C.

A does not exhibit stereoisomerism.

B and C are a pair of stereoisomers.

Products D and E are alcohols.

D and E are a pair of enantiomers.

Deduce the name of isomer A. Explain why A does not exhibit stereoisomerism. (2)

A = but-1-ene (1)

two groups/atoms/Hs the same on one of the C=C carbons (1)

Under suitable conditions, 2-bromobutane reacts with sodium hydroxide to

produce a mixture of five products, A, B, C, D and E.

Products A, B and C are alkenes.

A is a structural isomer of B and C.

A does not exhibit stereoisomerism.

B and C are a pair of stereoisomers.

Products D and E are alcohols.

D and E are a pair of enantiomers.

Deduce the name of isomer B and the name of isomer C. Explain the origin of the stereoisomerism in B and C. (2)

Z-but-2-ene AND E-but-2-ene (1)
lack of/restricted/no (free) rotation around C=C/double bond (1)

Compound J is one of a pair of stereoisomers

Explain:

• what stereoisomers are

• how E-Z stereoisomerism occurs

• how the Cahn-Ingold-Prelog rules can be used to decide whether compound J is an E or Z isomer. (6)

Stereoisomers are compounds with the same structural formula but a different arrangement of atoms in space.

E/Z isomerism arises due to restricted rotation around the C=C bond

When each C of C=C is attached to two different groups

CH₃CH₂ is higher priority than H on RHS C

as atomic number of C is higher than H or C = 6 v H = 1

(CH₃)₂CH is higher priority than CH₃CH₂ on LHS C

as atomic numbers of atoms joined to C (joined to C=C) are higher for (CH₃)₂CH than CH₃CH₂

highest priority groups on opposite sides (of C=C)

Therefore compound J is a Z isomer (6)