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Topic 20: Organic Chemistry
For HL students only
1. [1 mark]
Which compound has a chiral carbon?
A. Bromoethane
A. Bromoethane
B. 2-bromopropane
C. 2-bromobutane
D. 3-bromopentane
Markscheme
C
2. [1 mark]
Which statement best describes retrosynthesis?
A. The reaction conditions needed to convert the product of a reaction back to the starting materials.
A. The reaction conditions needed to convert the product of a reaction back to the starting materials.
B. Synthesizing a target molecule by working back from the target molecule to the starting materials.
C. A synthetic scheme using traditional methods rather than modern methods and materials.
D. A synthetic pathway which favours the equilibrium towards the products.
Markscheme
B
3. [1 mark]
What combination of reactants will convert nitrobenzene to phenylamine in two steps?
4a. [2 marks]
2-Bromobutane can react with cyanide, CN−, in a nucleophilic substitution reaction.
This reaction could proceed through either SN1 or SN2 mechanisms depending on the reaction conditions. Sketch a graph of the rate versus nucleophile concentration, [CN−], for each of the mechanisms.
4b. [1 mark]
Suggest, with a reason, whether the reaction follows an SN1 or SN2 mechanism if only one stereoisomer was obtained as a product.
Markscheme
SN2 AND SN2 «mechanism» occurs with inversion of configuration
OR
SN2 AND SN1 «mechanism» would create a racemic mixture ✔
Accept appropriate diagrams.
4c. [1 mark]
State an instrument that could be used to determine whether the product was a single enantiomer or a racemic mixture.
Markscheme
polarimeter ✔
4d. [1 mark]
SN1 and SN2 reactions are better conducted using different types of solvents. Identify two properties of a solvent most suited for the mechanism proposed in (b).
Markscheme
aprotic AND polar ✔
4e. [1 mark]
State, with a reason, how the rate of reaction of cyanide with 2-chlorobutane differs from its rate of reaction with 2-bromobutane under the same conditions.
Markscheme
slower AND C-Cl bond is stronger «than C-Br»
OR
slower AND Br/Br− is a better leaving group ✔
4f. [3 marks]
2-Bromobutane reacts with hydroxide via the same mechanism identified in (b). Explain this mechanism using curly arrows to represent the movement of electron pairs.
5. [1 mark]
What is the product of the reaction of propanal with lithium aluminium hydride, LiAlH4?
A. Propanoic acid
B. Propanone
C. Propan-1-ol
D. Propan-2-ol
Markscheme
C
6. [1 mark]
Which statement is correct about configurational isomers?
A. Configurational isomers can only be interconverted by breaking and reforming bonds.
B. Configurational isomers have different molecular formulas but the same structural formulas.
C. Configurational isomers are not distinct compounds.
D. Configurational isomers always have identical physical properties.
Markscheme
A
7. [1 mark]
Which product is formed when CH3COCH2CH3 is reduced with sodium borohydride?
A. CH3CH2CH2CHO
B. CH3CH2CH2CH2OH
C. CH3CH(OH)CH2CH3
D. CH3CH2CH2COOH
Markscheme
C
8. [1 mark]
Which attacking species is matched with its mechanism of reaction?
Markscheme
D
9. [1 mark]
Which is most likely to hydrolyse via a SN1 mechanism?
A. CH3CHBrCH2CH3
B. (CH3)2CHBr
C. (CH3)3CBr
D. CH3CH2CH2CH2Br
Markscheme
C
10. [1 mark]
Which compound rotates the plane of plane-polarized light?
A. CH3C(CH3)ClCH3
B. CH3CH2CHClCH3
C. CH3C(Cl)2CH3
D. CH3CClBrCH3
Markscheme
B
11. [1 mark]
Which is the electrophile in the nitration of benzene?
A. HNO3
B. NO2+
C. NO2-
D. NH4+
Markscheme
B
12. [1 mark]
What will be the major product in the reaction between but-1-ene and Hbr?
A. 2-bromobut-1-ene
B. 1-bromobut-1-ene
C. 2-bromobutane
D. 1-bromobutane
Markscheme
C
13. [1 mark]
Which molecule has an enantiomer?
A. CH3CH2CHOHCH2CH3
B. CH2OHCH2CH2CH=CH2
C. CH3CH2CH2CH=CHBr
D. CH3CHBrCH2CH2CH3
Markscheme
D
14a. [1 mark]
Chlorine undergoes many reactions.
State the full electron configuration of the chlorine atom.
Markscheme
1s22s22p63s23p5 ✔
Do not accept condensed electron configuration.
14b. [1 mark]
State, giving a reason, whether the chlorine atom or the chloride ion has a larger radius.
Markscheme
Cl- AND more «electron–electron» repulsion ✔
Accept Cl- AND has an extra electron.
14c. [2 marks]
Outline why the chlorine atom has a smaller atomic radius than the sulfur atom.
Markscheme
Cl has a greater nuclear charge/number of protons/Zeff «causing a stronger pull on the outer electrons» ✔
same number of shells
OR
same «outer» energy level
OR
similar shielding ✔
OR
same «outer» energy level
OR
similar shielding ✔
15. [1 mark]
In which compound is the halogen substituted the most rapidly by aqueous hydroxide ions?
A. (CH3)3CCl
B. (CH3)3CI
C. CH3CH2CH2CH2Cl
D. CH3CH2CH2CH2I
Markscheme
B
16. [1 mark]
Which can be reduced to an aldehyde?
A. Butanone
B. Butan-1-ol
C. Butanoic acid
D. Butan-2-ol
Markscheme
C
17. [1 mark]
Which can show optical activity?
A. CHBrCHCl
B. CH3CH2CHBrCH2CH3
C. (CH3)2CBrCl
D. CH3CH2CH(CH3)Br
Markscheme
D
18a. [1 mark]
Taxol is an anticancer drug.
State the feature of Taxol that is a major challenge in its synthesis. Use section 37 of the data booklet.
Markscheme
numerous stereoisomers/chiral carbons/chiral centres/stereocentres/optical isomers ✔
NOTE: Accept exact number of chiral carbons ie 11, but do not accept just “chiral”.
18b. [1 mark]
Describe how the challenge in (a) was resolved by pharmaceutical companies.
Markscheme
chiral auxiliaries/molecule binds to reactant blocking one reaction site «by steric hindrance»
OR
asymmetric synthesis / enantioselective catalysis «producing a specific enantiomer»
OR
biosynthesis / genetically modified bacteria/microorganisms ✔
OR
asymmetric synthesis / enantioselective catalysis «producing a specific enantiomer»
OR
biosynthesis / genetically modified bacteria/microorganisms ✔
NOTE: Accept “use of a chiral auxiliary leading to «the synthesis of» the desired enantiomer”.
19. [1 mark]
Which is a major product of the electrophilic addition of hydrogen chloride to propene?
A. ClCH2CH=CH2
B. CH3CH(Cl)CH3
C. CH3CH2CH2Cl
D. CH3CH=CHCl
Markscheme
B
20. [1 mark]
Which solvent is aprotic?
A. H2O
B. C6H5CH3
C. CH3OH
D. CH3NH2
Markscheme
B
21. [1 mark]
Which statement is not correct regarding benzene?
A. It is planar.
B. The ring contains delocalized electrons.
C. It always reacts in the same way as alkenes.
D. The carbon–carbon bond has a bond order of 1.5.
Markscheme
C
22. [1 mark]
Which compound exists as two configurational isomers?
A. CBr2=CH2
B. CH2=CHBr
C. CHBr2CH2Br
D. CHBr=CHBr
Markscheme
D
23. [1 mark]
Which class of compound is formed when a ketone is reduced?
A. primary alcohol
B. secondary alcohol
C. ether
D. carboxylic acid
Markscheme
B
24. [1 mark]
Which statement about the reaction of a hydroxide ion with the organic reagent is correct?
A. 1-bromopentane predominantly follows an SN1 mechanism.
B. 2-bromo-2-methylbutane predominantly follows an SN2 mechanism.
C. Reaction with 1-bromopentane occurs at a slower rate than with 1-chloropentane.
D. Reaction with 1-bromopentane occurs at a slower rate than with 2-bromo-2-methylbutane.
Markscheme
D
25. [1 mark]
What is the major product of the reaction of HBr with but-1-ene?
A. 1-bromobutane
B. 2-bromobutane
C. 1,2-dibromobutane
D. 2,2-dibromobutane
Markscheme
B
26. [1 mark]
How many chiral carbon atoms are present in one molecule of (CH3)2CHCHClCHBrCH3?
A. 0
B. 1
C. 2
D. 3
Markscheme
C
27a. [1 mark]
Halogenoalkanes undergo nucleophilic substitution reactions with sodium hydroxide.
State a reason why most halogenoalkanes are more reactive than alkanes.
Markscheme
polarity/polar «molecule/bond»
OR
carbon–halogen bond is weaker than C–H bond ✔
OR
carbon–halogen bond is weaker than C–H bond ✔
27b. [1 mark]
Classify 1-bromopropane as a primary, secondary or tertiary halogenoalkane, giving a reason.
Markscheme
primary AND Br/bromine is attached to a carbon bonded to two hydrogens
OR
primary AND Br/bromine is attached to a carbon bonded to one C/R/alkyl «group» ✔
OR
primary AND Br/bromine is attached to a carbon bonded to one C/R/alkyl «group» ✔
Accept “primary AND Br/bromine is attached to the first carbon in the chain”
27c. [4 marks]
Explain the mechanism of the reaction between 1-bromopropane with aqueous sodium hydroxide using curly arrows to represent the movement of electron pairs.
27e. [2 marks]
Suggest two advantages of understanding organic reaction mechanisms.
Markscheme
Any two of:
choose «most» appropriate reaction «for preparing the target compound» ✔
design/discover new reactions/reagents ✔
apply this knowledge to other areas of chemistry/science ✔
«retro-»synthesis «more effective» ✔
control/predict «desired» products ✔
control rate of reaction «more effectively» ✔
satisfy intellectual curiosity ✔
predicting how changing reagents/conditions might affect reaction ✔
suggesting intermediates/transition states ✔
choose «most» appropriate reaction «for preparing the target compound» ✔
design/discover new reactions/reagents ✔
apply this knowledge to other areas of chemistry/science ✔
«retro-»synthesis «more effective» ✔
control/predict «desired» products ✔
control rate of reaction «more effectively» ✔
satisfy intellectual curiosity ✔
predicting how changing reagents/conditions might affect reaction ✔
suggesting intermediates/transition states ✔
Accept other reasonable answers
28. [1 mark]
What is name of this compound applying IUPAC rules?
A. E 1-bromo-1-chlorobut-1-ene
B. Z 1-bromo-1-chlorobut-1-ene
C. E 1-bromo-1-chloro-2-ethylethene
D. Z 1-bromo-1-chloro-2-ethylethene
Markscheme
B
29. [1 mark]
Which molecule contains a chiral carbon?
A. CH3CH2CHBrCH2CH3
B. CH3CH2CHBrCH3
C. CH2BrCH(CH3)CH2Br
D. CH3CH2CH2CH2CH2Br
Markscheme
B