Which molecule has a chiral centre?

A.     \({\text{C}}{{\text{H}}_{\text{3}}}{\text{CH=CHCHO}}\)

B.     \({{\text{(C}}{{\text{H}}_{\text{3}}}{\text{)}}_{\text{2}}}{\text{C=CHC}}{{\text{H}}_{\text{2}}}{\text{OH}}\)

C.     \({\text{C}}{{\text{H}}_{\text{3}}}{\text{OC}}{{\text{H}}_{\text{2}}}{\text{C}}{{\text{H}}_{\text{3}}}\)

D.     \({\text{C}}{{\text{H}}_{\text{3}}}{\text{CHOHC}}{{\text{H}}_{\text{2}}}{\text{C}}{{\text{H}}_{\text{3}}}\)

D

In this question, candidates had to identify which molecule had a chiral centre. One respondent stated that ethers are off-syllabus. It is true that as a functional group, ethers are not required based on Topic 10. However, it should be noted that candidates are expected to know that oxygen is divalent and hence can occur with two single bonds. This is also referred to in the Teacher’s notes corresponding to AS 4.3.2, where a comparison between the intermolecular forces present in \({\text{C}}{{\text{H}}_{\text{3}}}{\text{OC}}{{\text{H}}_{\text{3}}}\) and \({\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{OH}}\) is referred to. Hence, candidates are expected to be able to write a full structural formula from the condensed structural formula of \({\text{C}}{{\text{H}}_{\text{3}}}{\text{OC}}{{\text{H}}_{\text{2}}}{\text{C}}{{\text{H}}_{\text{3}}}\) to determine that it does not have a chiral centre.