DP Chemistry (first assessment 2025)
Question 19M.2.HL.TZ2.6d(i)
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.2.HL.TZ2.6d(i) |
| Level | HL | Paper | 2 | Time zone | TZ2 |
| Command term | Outline | Question number | d(i) | Adapted from | N/A |
d(i).
[Maximum mark: 2]
19M.2.HL.TZ2.6d(i)
(d(i))
Outline why the major product, C6H5–CHBr–CH3, can exist in two forms and state the relationship between these forms.
Two forms:
Relationship:
[2]
Markscheme
Two forms:
chiral/asymmetric carbon
OR
carbon atom attached to 4 different groups [✔]
Relationship:
mirror images
OR
enantiomers/optical isomers [✔]
Note: Accept appropriate diagrams for either or both marking points.
Examiners report
Candidates were given the products of the addition reaction and asked about the major product. Perhaps they were put off by the term “forms” and thus failed to “see” the chiral C that allowed the existence of enantiomers. There was some confusion with the type of isomerism and some even suggested cis/trans isomers.
Syllabus sections
Structure 3. Classification of matter » Structure 3.2—Functional groups: Classification of organic compounds » Structure 3.2.7—Stereoisomers have the same constitution (atom identities, connectivities and bond multiplicities) but different spatial arrangements of atoms. Describe and explain the features that give rise to cis-trans isomerism; recognize it in non-cyclic alkenes and C3 and C4 cycloalkanes. Draw stereochemical formulas showing the tetrahedral arrangement around a chiral carbon. Describe and explain a chiral carbon atom giving rise to stereoisomers with different optical properties. Recognize a pair of enantiomers as non-superimposable mirror images from 3D modelling (real or virtual).