135 exam-style questions on Functional groups: classification of organic compounds — topic S3.2 of Structure 3: Classification of matter in the IB Chemistry syllabus — with answers and explanations. Samples below; the full set is free with an account.
In the mass spectrum of a compound, what does the peak at the highest m/z value (the molecular ion peak, M+) tell you?
Answer: The relative molecular mass of the compound
The molecular ion peak (M+) corresponds to the whole molecule that has lost one electron. Its m/z value equals the relative molecular mass of the compound. Fragment peaks at lower m/z arise when the molecular ion breaks apart, helping to deduce structure.
A broad absorption at about 3200-3550 cm-1 in an infrared spectrum indicates the presence of which functional group?
Answer: O-H (hydroxyl or acid)
A broad absorption around 3200-3550 cm-1 is characteristic of the O-H bond stretch in alcohols (and even broader for carboxylic acids). The C=O carbonyl stretch appears near 1700 cm-1, so IR distinguishes functional groups by their absorption ranges.
What is the general formula of the alkanes?
Answer: CₙH₂ₙ₊₂
Saturated hydrocarbons follow CₙH₂ₙ₊₂ (e.g. methane CH₄, ethane C₂H₆). Alkenes, which have one double bond, follow CₙH₂ₙ.
By which mechanism does a tertiary halogenoalkane undergo nucleophilic substitution?
Answer: SN1
A tertiary halogenoalkane forms a relatively stable tertiary carbocation, favouring the two-step SN1 mechanism. Primary halogenoalkanes favour the one-step SN2 mechanism.
Identify the functional group present in the compound CH3CH2CHO.
Answer: Carbonyl of an aldehyde
The -CHO group is a carbonyl at the end of the chain, characteristic of an aldehyde (propanal).
State the class of organic compound represented by the general formula R-O-R', where R and R' are alkyl groups.
Answer: Ether
An oxygen atom bonded between two alkyl (carbon) groups, R-O-R', defines an ether.
That was 6 of 135 Functional groups: classification of organic compounds questions.
Practise all 135 freeStateAO1 · 1–2 marks
One word or one short sentence. No explanation, no working: the mark is for the fact itself.
DeduceAO2 · 1–4 marks
Reach the conclusion from the information given, showing the chain of reasoning.
IdentifyAO1 · 1–2 marks
Name or pick out the thing asked for from the information given. A label, not a paragraph.
135 Functional groups: classification of organic compounds questions — free with an account. Spaced repetition, streaks and full exam simulations included.
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