CAIE A-Level Chemistry 13.4.4 Chiral Centres and Enantiomers

Practise identifying carbon atoms bonded to four different groups and drawing the resulting pair of optical isomers.

Exam points

identify a chiral carbon only when it is tetrahedral and bonded to four different atoms or groups
draw the two enantiomers with consistent wedge-and-dash geometry as non-superimposable mirror images
inspect every candidate centre in a complex molecule without introducing meso or diastereoisomer terminology

[Maximum number: 3]

$4\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCHO}$ is used in the synthesis of some antibiotics.

(a)

X, Y and Z are all isomers of $\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCHO}$ .

A summary of some of the reactions and properties of X, Y and Z is shown in the table.

Table for Question (a) — CAIE A-Level Chemistry AS

[ 3 ]

(i)

Y has a chiral centre and exists as a pair of optical isomers.

State what is meant by the term chiral centre.

[ 1 ]

(ii)

Draw the optical isomers of Y using the conventional three-dimensional representation.
$\mathbf{Z}, \mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}$ , has a branched carbon chain. It shows geometrical isomerism.

[ 2 ]

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13.4.4—Chiral centres and enantiomers question 1

Question (a)

Question (i)

Question (ii)