Spectroscopic identification of organic compounds
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Flip to reveal answersWhat does the molecular ion M⁺ tell you?
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All 12 Flashcards — Spectroscopic identification of organic compounds
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Question
What does the molecular ion M⁺ tell you?
Answer
Its m/z value is the **relative molecular mass (Mr)** — M⁺ is the peak at the **highest** m/z.
Question
What does a fragment peak tell you?
Answer
The **mass lost** (M⁺ − fragment) shows which **group broke off** (e.g. loss of 15 = CH_{3}).
Question
Loss of 15 in a mass spectrum means what?
Answer
Loss of a **CH_{3}** (methyl) group.
Question
Loss of 17 in a mass spectrum means what?
Answer
Loss of an **OH** group.
Question
What does infrared (IR) spectroscopy identify?
Answer
The **functional group**, from a characteristic absorption **wavenumber** (cm⁻¹) given in the data booklet.
Question
Which group gives a broad IR peak at 3200–3600 cm⁻¹?
Answer
An **O–H** group (an alcohol). A carboxylic acid O–H is even broader, ~2500–3000.
Question
Which group gives a sharp IR peak near 1700 cm⁻¹?
Answer
A **C=O** (carbonyl) — aldehyde, ketone, acid or ester.
Question
What does ¹H NMR tell you at SL?
Answer
The **number of peaks = number of different hydrogen environments** in the molecule.
Question
How many ¹H NMR peaks does ethanol (CH_{3}CH_{2}OH) give?
Answer
**Three** — the CH_{3}, CH_{2} and OH hydrogens are three different environments.
Question
Why does propanone (CH_{3}COCH_{3}) give one ¹H NMR peak?
Answer
By **symmetry** the two CH_{3} groups are equivalent, so all six H are in one environment.
Question
Which three techniques deduce an organic structure?
Answer
**MS** (Mr + fragments), **IR** (functional group), **¹H NMR** (number of H environments) — used together.
Question
Where is the IR absorption table found in the exam?
Answer
In the **data booklet** — you read the wavenumbers off, you don't memorise them.
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Full study notes for Spectroscopic identification of organic compounds
Topic 3.2 hub
Functional groups: classification of organic compounds
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