Identify the chiral centre in this enantiomer with an asterisk, *.

The \(( + )d\)-enantiomer has the characteristic smell of oranges and the \(( - )l\)-enantiomer has the characteristic smell of lemons. Explain the meaning of the \(( + )d\) and \(( - )l\) symbols used in this notation.

The R, S notation is also used. The \(( + )d\)-enantiomer is often described as R-limonene and the \(( - )l\)-enantiomer as S-limonene. Explain what is meant by the R, S notation and state whether the structure shown is R or S.

dextro/\(d\) and levo/\(l\) refer to right and left-handed / clockwise and anti-clockwise rotation of plane polarized light;

clockwise and anti-clockwise sequence of prioritized atoms (working from high to low atomic numbers) / OWTTE;

Allow absolute configuration of enantiomers.

Allow convention for labelling chiral carbon atoms using the Cahn-Ingold-Prelog notation.

S;

In (a), surprisingly a number of students were not able to identify the chiral centre.

Although some knew what \(d\) and \(l\) referred to, a number did not refer to plane-polarized light.

R and S notation was not understood and only the best candidates were able to determine the structure as S. Some simple class exercises on chiral centres, \(d\) and \(d\) notation and R and S notation using a number of simple molecules would greatly improve student understanding of this topic.