(a)[2]
Give the structural formulae for the pair of chain isomers of $\text{C}_4\text{H}_8\text{O}_2$ that are carboxylic acids.
(b(i))[2]
Give the structural formulae for a pair of positional isomers with the formula $\text{C}_4\text{H}_8\text{O}_2$ that are esters.
(b(ii))[2]
Give the reagents and conditions required to make one of your esters in (i).
(c)[3]
Explain how these two spectra differ, especially in relation to the peaks with wavenumbers above $1500\,\text{cm}^{-1}$.