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 E isomer (6)

1-chloropropane can also be produced by the reaction between propane and chlorine in the presence of ultraviolet light. State why ultraviolet light is needed for this reaction to occur. (1)

provides energy to break (covalent) bond in chlorine

OR

to form chlorine free radicals (1)

Explain the differences between structural isomerism and stereoisomerism. Use examples to show how compounds with the molecular formula C₄H₈ exhibit stereoisomerism and the three types of structural isomerism. (6)

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

This occurs as there is a restricted rotation around the C=C bond

Structure of E and Z-but-2-ene

correct identity of E and Z isomers

Structural isomers are compounds with the same molecular formula but have a different structural formula

Structural isomers
different C chain, e.g. methylpropene & but-1-ene / but-2-ene
different position of functional group e.g. but-1-ene & but-2-ene
different functional group, e.g. cyclobutane & but-1-ene / but-2-ene / methylpropene

Which is the major product of the reaction between 2-methylbut-2-ene and iodine monochloride (ICl)? (1)

C (1)

This is because ICl is polarised as Iδ⁺—Clδ⁻

How many structural isomers with an unbranched carbon chain have the molecular formula C₄H₈Br₂?

A 4

B 5

C 6

D 7 (1)

C (1)

• 1,1-dibromobutane

• 1,2-dibromobutane

• 1,3-dibromobutane

• 1,4-dibromobutane

• 2,2-dibromobutane

• 2,3-dibromobutane