This question is about six isomers of C8H16O2 - AQA - A-Level Chemistry - Question 10 - 2017 - Paper 2

The combustion equation for isomer P can be written as:

$C_8H_{16}O_2 + aO_2 → bCO_2 + cH_2O$

Where the stoichiometry needs to be balanced according to the combustion. To calculate the mass of P used, we first determine the moles of $CO_2$ produced:

1. Calculate moles of $CO_2$: [ n_{ ext{CO}2} = \frac{V}{RT} = \frac{270 ext{ cm}³ imes 1 ext{ dm}³/1000 ext{ cm}³}{8.31 ext{ JK}^{-1} ext{mol}^{-1} imes 298 ext{ K}} ] [ n{ ext{CO}_2} = \text{value} ]

2. Calculate moles of P: Given the stoichiometry in typical combustion, find the mass using the molar mass of P.

The structure of Q can be identified as 3-hydroxybutanoic acid. Evidence from Figure 4 indicates a distinct peak pattern, while Figure 5 shows specific carbon environments consistent with this structure.

R has 5 peaks because each carbon environment is unique. In contrast, S features overlap in its carbon environments resulting in 4 peaks overall, confirming the statement.

For R, we observe a triplet and a quartet in its 1H spectrum which indicates non-equivalent environments. S, however, displays only singlets, allowing for clear differentiation. R has 3 peaks whereas S has 2 peaks in this splitting analysis.

The structure of T is shown as a cyclic compound resulting from dehydration of 5-hydroxyhexanoic acid, depicted as follows:

The repeating unit of the polyester formed by 5-hydroxyhexanoic acid can be represented as follows:

The polymer formed by U lacks the chemical groups needed for hydrolysis under environmental conditions, whereas the ester groups in the other polymer are more susceptible to enzymatic attack.