S3.2 Functional groups
Practice exam-style IB Chemistry questions for Functional groups, aligned with the syllabus and grouped by topic.
Question 1
A compound has the condensed structural formula CH3CH2CH2OH. What is its molecular formula?
A.
C2H6O
B.
C3H8O
C.
C3H6O
D.
C3H7O
Question 2
What is the functional group in CH3COOH?
A.
Alkoxy
B.
Carbonyl
C.
Hydroxy
D.
Carboxyl
Question 3
What is the general formula for an acyclic alkene containing one carbon–carbon double bond?
A.
CnH2n+2
B.
CnH2n−2
C.
CnH2n
D.
CnH2n+1X
Question 4
What is the IUPAC name of CH3CH(Cl)CH2CH3?
A.
3-chlorobutane
B.
1-chlorobutane
C.
2-chlorobutane
D.
2-chloropropane
Question 5
What term describes CH3CH=CH2?
A.
Saturated hydrocarbon
B.
Unsaturated hydrocarbon
C.
Halogenoalkane
D.
Alcohol
Question 6
What is a racemic mixture?
A.
A mixture of conformations formed by rotation about single bonds.
B.
A mixture of structural isomers with the same molecular formula.
C.
A mixture containing equal masses of cis and trans isomers.
D.
A 1:1 mixture of two enantiomers of the same compound.
Question 7
The skeletal formula of an unbranched four-carbon alcohol has a terminal –OH group.
State the molecular formula.
[1]
Give a condensed structural formula.
[1]
State one feature that would be shown in a full structural formula but omitted from a skeletal formula.
[1]
Question 8
For each compound, identify the principal functional group.
CH3CH2Br
[1]
CH3CONH2
[1]
CH3COOCH2CH3
[1]
Question 9
Pentane has a higher boiling point than propane. What is the best explanation?
A.
Pentane molecules contain stronger covalent C–C bonds than propane molecules.
B.
Pentane molecules form hydrogen bonds whereas propane molecules do not.
C.
Pentane molecules have stronger London dispersion forces because they have more electrons and a larger surface area.
D.
Pentane molecules have permanent dipoles but propane molecules are non-polar.
Question 10
What type of structural isomerism is shown by butan-1-ol and butan-2-ol?
A.
Functional group isomerism
B.
Stereoisomerism
C.
Chain isomerism
D.
Position isomerism
Question 11
What is the classification of (CH3)3COH as an alcohol?
A.
Secondary
B.
Tertiary
C.
Quaternary
D.
Primary
Question 12
What structural feature is required for cis–trans isomerism in a non-cyclic alkene?
A.
The molecule contains only carbon and hydrogen atoms.
B.
The molecule contains a carbonyl group next to the C=C bond.
C.
Each carbon atom of the C=C bond is attached to two different groups.
D.
At least one carbon atom of the C=C bond is attached to two identical groups.
Question 13
A tetrahedral carbon atom is bonded to –H, –CH3, –CH2CH3 and –Cl. What is true of this carbon atom?
A.
It is chiral because it is bonded to four different groups.
B.
It is not chiral because it is tetrahedral.
C.
It is not chiral because it contains a halogen atom.
D.
It is chiral only if it is part of a ring.
Question 14
The mass spectrum of an organic compound has its highest significant peak at m/z 74. What information is obtained from this peak, assuming a singly charged molecular ion?
A.
The base peak has relative intensity 74%.
B.
The relative molecular mass is 74.
C.
The empirical formula is C7H4.
D.
The compound contains exactly 74 carbon atoms.
Question 15
An IR spectrum shows a strong absorption in the functional group region near 1700 cm−1 and no broad absorption in the O–H region. What functional group is most directly indicated?
A.
N–H
B.
O–H
C.
C–Cl
D.
C=O
Question 16
In high-resolution 1H NMR, a signal has two equivalent neighbouring hydrogen atoms on adjacent carbon atoms. What splitting pattern is expected?
A.
Singlet
B.
Doublet
C.
Triplet
D.
Quartet
Question 17
A straight-chain compound contains one carboxyl group and has five carbon atoms.
State the homologous series.
[1]
State the general formula for this homologous series.
[1]
Deduce the molecular formula of the five-carbon compound.
[1]
Question 18
Butan-1-ol has a higher boiling point than butane.
State the strongest type of intermolecular force present between butan-1-ol molecules.
[1]
Explain why butan-1-ol has the higher boiling point.
[1]
Question 19
Consider the compound CH3CH(CH3)CH2CHO.
State the principal functional group.
[1]
State the number of carbon atoms in the parent chain.
[1]
Give the IUPAC name.
[1]
Question 20
Classify each compound as primary, secondary or tertiary.
CH3CH2CH2Cl as a halogenoalkane
[1]
CH3CH(OH)CH3 as an alcohol
[1]
(CH3)3N as an amine
[1]
Question 21
The graph shows boiling points of the first six straight-chain alkanes.
Describe the trend shown by the data.
[1]
Explain the trend in terms of intermolecular forces.
[1]
Suggest why extrapolating this graph to very large values of n may be less reliable than interpolation.
[1]
Question 22
The figure shows three representations of the same compound: a ball-and-stick model, a skeletal formula and a condensed structural formula.
State the molecular formula of the compound.
[1]
Identify the functional group present.
[1]
Explain one advantage of the skeletal formula over the ball-and-stick model for exam communication.
[1]
Explain one advantage of the ball-and-stick model over the condensed structural formula.
[1]
State why none of the three representations alone is a complete model of the real molecule.
[1]
Question 23
Propanone, CH3COCH3, gives how many signals in a low-resolution 1H NMR spectrum?
A.
Three
B.
Two
C.
One
D.
Six
Question 24
A compound has molecular formula C3H6O. Its IR spectrum shows a strong C=O absorption and its 1H NMR spectrum has one signal only. What structure is most consistent with the data?
A.
CH2=CHCH2OH
B.
CH3COCH3
C.
CH3OCH=CH2
D.
CH3CH2CHO
Question 25
The compounds CH3CH2CH2CH3 and (CH3)3CH have the same molecular formula.
State their molecular formula.
[1]
State the type of structural isomerism shown.
[1]
Explain why they are structural isomers.
[1]
Question 26
A ball-and-stick model is used to represent ethanol.
State one advantage of this model compared with a condensed structural formula.
[1]
State one limitation of this model for determining the molecular formula.
[1]
Give two features of carbon bonding that help explain the large number of organic compounds.
[1]
Question 27
But-2-ene shows cis–trans isomerism but but-1-ene does not.
State the feature of a C=C bond that allows cis–trans isomerism.
[1]
Explain why but-1-ene does not show cis–trans isomerism.
[1]
Question 28
A molecule contains a carbon atom bonded to –OH, –H, –CH3 and –CH2CH3.
State whether this carbon atom is chiral.
[1]
Explain your answer.
[1]
State the relationship between the two stereoisomers that arise from this carbon atom.
[1]
Question 29
A mass spectrum of a compound shows a molecular ion peak at m/z 60 and a strong fragment peak assigned to COOH+.
State the meaning of the molecular ion peak.
[1]
Deduce the relative molecular mass of the compound.
[1]
Suggest a functional group consistent with the fragment peak.
[1]
Question 30
Carbon dioxide is a greenhouse gas even though it has no permanent dipole.
State what is meant by an IR active vibration.
[1]
Explain why some vibrations of CO2 absorb infrared radiation.
[1]
Question 31
An organic compound has an IR spectrum with a broad absorption in the O–H region and a strong absorption in the C=O region.
Identify one functional group consistent with both absorptions.
[1]
State why IR spectroscopy alone may not determine the complete structure.
[1]
State the usual unit for wavenumber in an IR spectrum.
[1]
Question 32
A high-resolution 1H NMR spectrum contains a signal for a CH3 group next to a CH2 group.
State the number of neighbouring hydrogen atoms causing splitting of the CH3 signal.
[1]
Deduce the multiplicity of the CH3 signal.
[1]
State the relative peak heights for this multiplicity.
[1]
State the rule used.
[1]
Question 33
The table gives condensed structural formulas for four organic compounds.
| Compound | Condensed structural formula |
|---|---|
| A | CH3CH2COOH |
| B | CH3CH(Br)CH3 |
| C | CH3CH2CHO |
| D | CH3COCH3 |
Identify the compound that is a carboxylic acid.
[1]
Name the compound with formula CH3CH(Br)CH3.
[1]
State the homologous series for CH3CH2CHO.
[1]
Identify one pair of functional group isomers in the table.
[1]
Question 34
The graph compares boiling points of unbranched alcohols and unbranched alkanes with the same number of carbon atoms.
State which homologous series has higher boiling points over the range shown.
[1]
Explain the difference between the two series.
[1]
Suggest why the difference between successive alcohols becomes larger or smaller less regularly than the alkane trend.
[1]
Question 35
The IR spectra of two compounds with molecular formula C3H6O are shown.
State the diagnostic absorption common to both spectra.
[1]
Identify the functional group indicated by this absorption.
[1]
Explain why the IR spectra alone may not distinguish the two structural isomers completely.
[1]
Suggest one additional technique that could distinguish the isomers.
[1]
Question 36
The low-resolution 1H NMR spectrum of CH3CH2Cl is considered.
State the number of 1H NMR signals expected.
[1]
State the integration ratio.
[1]
Explain why the chemical shift of the CH2 signal is expected to be larger than that of the CH3 signal.
[1]
Question 37
A compound has molecular formula C4H8O. IR spectroscopy shows a strong C=O absorption and no broad O–H absorption. Its 1H NMR spectrum has three signals with integration ratio 3:2:3.
State one functional group consistent with the IR data.
[1]
Suggest a structure consistent with all the data.
[1]
Explain how the NMR integration supports your structure.
[1]
Question 38
The figure shows four compounds with molecular formula C4H10O.
Identify one pair of position isomers.
[1]
Identify one pair of chain isomers.
[1]
Identify one pair of functional group isomers.
[1]
Classify the alcohol shown with the hydroxy group on carbon 2 as primary, secondary or tertiary.
[1]
Explain why all four compounds are structural isomers.
[1]
Question 39
A low-resolution 1H NMR spectrum and integration trace are shown for a compound with molecular formula C4H10O.
State the number of hydrogen environments.
[1]
State the integration ratio shown by the trace.
[1]
Deduce whether the spectrum is more consistent with butan-1-ol or ethoxyethane.
[1]
Explain your deduction using symmetry and integration.
[1]
Question 40
A high-resolution 1H NMR spectrum of a compound contains a triplet integrating to 3H and a quartet integrating to 2H, along with one additional singlet.
State the structural fragment indicated by the triplet and quartet.
[1]
Explain the splitting of the triplet.
[1]
Explain the splitting of the quartet.
[1]
Suggest why the additional singlet is not split by neighbouring hydrogens.
[1]
State one further item of spectral evidence needed to assign the complete structure.
[1]
Question 41
The mass spectra of two structural isomers with molecular formula C4H10O are shown.
State why the molecular ion peaks occur at the same m/z value.
[1]
Identify the spectrum with the stronger fragment peak assigned to CH2OH+.
[1]
Suggest the class of compound more likely to give the CH2OH+ fragment.
[1]
Explain how fragmentation can distinguish structural isomers with the same molecular formula.
[1]
Question 42
A student is given the compounds butane, butan-1-ol and butanoic acid.
Identify the organic class and principal functional group for butan-1-ol and butanoic acid.
[1]
Explain how functional groups and chain length influence physical and chemical properties in this set of compounds.
[1]
Question 43
Two compounds have the condensed structural formulas CH3CH2CH(CH3)CH2OH and CH3CH2COCH2CH3.
Identify the principal functional group in each compound.
[1]
Discuss how IUPAC rules are applied to name these compounds, including selection and numbering of the parent chain.
[1]
Question 44
Organic compounds may be represented by molecular, structural, skeletal and three-dimensional models.
State the information provided by an empirical formula and a molecular formula.
[1]
Evaluate the usefulness of different representations for identifying functional groups, atom counts and molecular shape.
[1]
Question 45
A compound has molecular formula C4H8O2. The figure gives its IR spectrum, mass spectrum and high-resolution 1H NMR summary.
| Method | Signal (cm^-1, m/z, ppm) | Size | Observation |
|---|---|---|---|
| IR | 1740 cm^-1 | strong | sharp absorption |
| IR | 1240 cm^-1 | strong | sharp absorption |
| IR | 2500-3300 cm^-1 | absent | no broad absorption |
| MS | m/z 88 | 18% | molecular ion peak |
| 1H NMR | δ 1.26 ppm | 3H | triplet, J = 7.1 Hz |
| 1H NMR | δ 2.04 ppm | 3H | singlet |
| 1H NMR | δ 4.12 ppm | 2H | quartet, J = 7.1 Hz |
| 1H NMR | δ 10-12 ppm | 0H | no resonance observed |
Identify the functional group indicated by the IR spectrum.
[1]
State the information provided by the molecular ion peak.
[1]
Use the NMR summary to identify an ethyl group.
[1]
Deduce a structure consistent with all the data.
[1]
Explain why a carboxylic acid is less consistent with the full data set.
[1]
Question 46
Compounds with molecular formula C4H8O can include aldehydes, ketones and unsaturated alcohols.
Define structural isomerism.
[1]
Compare chain, position and functional group isomerism using possible C4H8O examples.
[1]
Question 47
Stereoisomerism can arise from restricted rotation or from a chiral carbon atom.
State two conditions needed for cis–trans isomerism in a non-cyclic alkene.
[1]
Explain how a chiral carbon atom gives rise to optical isomerism, including the terms enantiomer and racemic mixture.
[1]
Question 48
A compound has molecular formula C3H6O. Two possible structures are propanal and propanone.
State one similarity and one difference in the IR spectra expected for these compounds.
[1]
Evaluate how 1H NMR and mass spectrometry could be used with IR spectroscopy to distinguish the two structures.
[1]
Question 49
Infrared spectroscopy is used to identify bonds in organic molecules and to explain absorption by greenhouse gases.
Define wavenumber and state its common unit in IR spectroscopy.
[1]
Discuss the factors that determine whether a molecular vibration absorbs infrared radiation and how IR evidence is used in functional group analysis.
[1]
Question 50
An unknown compound X has molecular formula C4H8O2. Its IR spectrum shows a strong C=O absorption and no broad O–H absorption. Its high-resolution 1H NMR spectrum shows three signals: a triplet integrating to 3H, a quartet integrating to 2H and a singlet integrating to 3H.
Identify two functional groups or classes that are consistent with the molecular formula and a C=O absorption.
[1]
Deduce the structure of X and justify your answer using all the spectral evidence.
[1]
The Fast Track To Your
Best IB Coursework & College Essays
All content on this website has been developed independently from and is not endorsed by the International Baccalaureate Organization. International Baccalaureate and IB are registered trademarks owned by the International Baccalaureate Organization.