Describe how 2,4-dinitrophenylhydrazine (2,4-DNP) can be used to confirm the presence of a carbonyl group, and explain how the solid product obtained can subsequently identify the specific aldehyde or ketone without using spectroscopy.

Describe a specific chemical test, including the reagent and expected observations, to distinguish whether an unknown carbonyl compound is an aldehyde or a ketone.

A chemist is investigating two structural isomers, X and Y, which both contain a carbonyl group.

Quantitative analysis reveals that both compounds have the following percentage composition by mass: $C:69.77\%$; $H:11.63\%$; $O:18.60\%$

The mass spectra of the two compounds show the following key features:

• Compound X has a molecular ion peak at $m/z=86$ and a prominent fragment peak at $m/z=57$.
• Compound Y has a molecular ion peak at $m/z=86$ and a prominent fragment peak at $m/z=43$.

Deduce the molecular formula of X and Y. Identify the structures of both compounds, giving their IUPAC names and drawing their structural formulas. Identify the species responsible for the key fragment peaks at $m/z=57$ and $m/z=43$.

An organic compound Z contains carbon, hydrogen, and oxygen only, with a relative molecular mass ($M_r$) of $128.0$. Compound Z has two carbonyl groups and contains no other functional groups.

The ${}^{1}H$ NMR spectrum of Z in a deuterated solvent shows the following peaks:

• A singlet at $\delta =3.6ppm$ (relative peak area = 2)
• A quartet centred at $\delta =2.5ppm$ (relative peak area = 4)
• A triplet centred at $\delta =1.0ppm$ (relative peak area = 6)

Analyse this NMR spectrum to deduce a possible structure for compound Z. Fully justify your answer by assigning each peak to the corresponding proton environment in the proposed structure.