Section IB 1

Two reactions of an alkene, B, are shown below.

[A] C₄H₁₀ <---(H₂/Ni)------ [B] CH₂-CH=CH-CH₂ (trans) ------> [C] C₄H₉Br

a) State the name of A and write an equation for its complete combustion. Explain why the incomplete combustion of A is dangerous.

ans a) (i)

Compound A is butane.

Combustion:

2C₄H₁₀ + 13O₂ 8CO₂ + 10H₂O

Incomplete combustion produces carbon monoxide gas, which is colourless odourless and poisonous.

ii) Outline a test to distinguish between A and B stating the result in each case.

ans a) (ii)

B is an alkene and will turn bromine water from orange to colourless. A is an alkane and as such, has no effect on bromine water.

iii) Write an equation for the conversion of B to C. State the type of reaction taking place and draw the structure of C.

ans a) (iii)

CH₂-CH=CH-CH₂ + HBr CH₂-CH₂-CHBr-CH₂

This is an example of electrophilic addition.

2-bromobutane

b) A compound D has a molecular formula C₂H₄O2 and is obtained from a reaction between methanol and methanoic acid. Write an equation for this reaction and state the name of D.

ans (b)

CH₃OH + HCOOH HCOOCH₃ + H₂O

D is methyl methanoate

c) A second compound E has the same molecular formula as D and has acidic properties. State the name of compound E.

ans (c)

The acidic isomer of methyl methanoate is ethanoic acid, CH₃COOH.

d) The first synthetic thread was made from a polyester. A section of the polyester is drawn below:

-----CH₂COO------CH₂COO-----CH₂COO-----

Give the structural formula of the monomer (containing two functional groups) that could be used to make this polyester and state the names of the two functional groups.

ans (d)

The polymer contains ester linkages, and so must be formed from condensation (esterification) of a carboxylic acid group and an alcohol group.

hydroxyethanoic acid

e) State, giving a reason, whether this polyester is made by a condensation or an addition reaction.

ans (e)

The polymerisation reaction consists of addition of two molecules, followed by elimination of a water molecule each time the polymer adds another monomer unit. Addition elimination is also called condensation.