Organic Chemistry: Carboxylic Acids (Edexcel International A Level Chemistry): Exam Questions

This question is about carboxylic acids and their derivatives.

Lactic acid, CH₃CH(OH)COOH, is produced in muscles as a result of anaerobic respiration.

i) The structure of lactic acid is

Give a reason why lactic acid shows optical isomerism.

(1)

ii) A laboratory sample of lactic acid does not rotate the plane of plane-polarised monochromatic light.

Give a reason for this observation.

(1)

iii) Give the structure of the organic product formed when lactic acid reacts with concentrated phosphoric(V) acid, H₃PO₄.

(1)

A reaction scheme involving butanoic acid is shown.

Identify X, Y and Z by name or formula.

The repeat unit of a polyester is shown.

Give the structures of the two monomers that could form this polyester.

An organic compound E contains carbon, hydrogen and oxygen only.

i) The accurate relative atomic masses, A_r , of the three elements in E are shown in the table.

E contains five carbon atoms and gives a molecular ion peak at m / z = 102.0678 in its mass spectrum.

Deduce the molecular formula of E.

(1)

ii) Aqueous sodium hydrogencarbonate is added to a sample of E.

No effervescence occurs.

State what can be deduced by this observation.

(1)

iii) The infrared spectrum of E has an absorption in the range 1750 – 1735 cm⁻¹. Name the functional group in E.

(1)

iv) Data from the high resolution proton NMR spectrum of E is shown.

Deduce the structure of E.

Justify your answer by labelling the protons responsible for each peak.

(3)