Alkenes

7 marks · Hard

This question is about isomerism in alkenes and addition reactions.

(a)

Butene (C4H8) has several isomers. Draw and name two different structural isomers of butene (use displayed formulae).

[2 marks]

(b)

But-1-ene reacts with hydrogen in an addition reaction. Write a balanced chemical equation for this reaction using molecular formulae.

[2 marks]

(c)

State the name and structural formula of the organic compound formed when but-2-ene reacts with steam.

[3 marks]

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

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(a) But-1-ene: ; But-2-ene: . Either displayed formulae or structural formulae accepted.

(b)

Common mistakes: Drawing same isomer twice; Product name confusion

Show mark scheme and worked solution

Marking points

B1 (a) · 1 mark · Correctly draws and names one isomer of butene (structural or displayed formula).

B2 (a) · 1 mark · Correctly draws and names a second, different isomer of butene (not a repeat or a rotation).

M1 (b) · 1 mark · Sets up: but-1-ene + hydrogen → alkane (butane).

A1 (b) · 1 mark · Correct balanced equation: .

M2 (c) · 1 mark · Identifies correct name of product: butan-2-ol.

M3 (c) · 1 mark · Gives correct structural formula: .

A2 (c) · 1 mark · Answer includes both name and structural formula for butan-2-ol, and identifies the addition of water to the double bond.

Worked solution

a) Two isomers of C4H8:

But-1-ene: displayed as . But-2-ene: displayed as .

b) But-1-ene reacts with hydrogen to form butane:

c) But-2-ene reacts with steam to form butan-2-ol. Structural formula: .