Question 23M.2.HL.TZ2.7
| Date | May 2023 | Marks available | [Maximum mark: 14] | Reference code | 23M.2.HL.TZ2.7 |
| Level | HL | Paper | 2 | Time zone | TZ2 |
| Command term | Deduce, Describe, Draw, Explain, Identify | Question number | 7 | Adapted from | N/A |
Hydrogen bromide, HBr, reacts with but-1-ene
Identify the type of reaction.
[1]
«electrophilic» addition/AE ✓
Do not accept nucleophilic addition.
Two products are possible.
Explain the mechanism for the formation of the major product, using curly arrows to indicate the movement of electron pairs.
[4]
curly arrow going from C=C to H of HBr AND curly arrow showing Br leaving ✓
correct representation of carbocation ✓
curly arrow going from lone pair/negative charge on Br− to C+ ✓
CH3CHBr(CH2CH3)/correct final product ✓
Award [3 max] for the correct mechanism of formation of the minor product.
Explain why the mechanism results in one product being formed in greater quantities than the other.
[2]
carbocation with ethyl group is stabilized
OR
secondary carbocation more stable «than primary carbocation» ✓
greater electron releasing/inductive effect of «two» electron releasing alkyl groups
«on secondary carbocation compared to one on primary carbocation» ✓
Do not accept ‘Markovnikov’s rule’ /C with most hydrogen atoms without reference to stability of carbocation.
Draw the structure of a section of a polymer formed from three monomers of but-1-ene.
[1]
Ignore brackets and ‘n’.
Continuation bonds must be shown.
Ethyl groups do not all have to be on one side.
Accept head-to-tail or head-to-head orientation of monomer units.
Deduce the hybridization of the first two carbon atoms in but-1-ene.
[1]
«both» sp2 ✓
Describe the bonding between the first two carbon atoms in but-1-ene in terms of orbitals on these atoms.
[3]
Any three of the following:
mixing of an s AND two p orbitals forms «three» sp2 /hybrid orbitals ✓
σ bond is overlap «of sp2 orbitals» along axial/internuclear axis
OR
head-on/end-to-end overlap «of sp2 orbitals» ✓
one p electron from each C does not hybridize ✓
bond is overlap «of p-orbitals» above and below internuclear axis
OR
sideways overlap «of parallel p orbitals» ✓
Accept suitable diagrams.
One isomer of C4H9Br can exist as stereoisomers. Draw the three-dimensional structures of the two stereoisomers using wedge-dash notation, clearly showing the relationship between them.
[2]
correct isomer ✓
mirror image shown clearly ✓
Do not accept Fischer projections.