b$.$ Compounds $P$ and $Q$ can undergo a Diels$-$Alder reaction to form two

regioisomeric products $R$ and $S$ as shown in Figure $5.$

longrightarrow,$C_8{H}_{12}{O}_2$

$C_8{H}_{12}{O}_2$

R

S

Figure $5$

$($i$)$ Draw the chemical structures of regioisomeric compounds $R$ and $S.$

$[2$ marks$]$

$($ii$)$ Using possible resonance contributors of $P$ and $Q$ predict which of the two

regioisomers will be favoured in the reaction.

$[6$ marks$]$

$($iii$)$ Using curly arrows, draw the mechanism for the reaction of $P$ and $Q$ to form the

dominant regioisomer you have predicted in your answer to part $($ii$)$ above.

$[2$ marks$]$