What analytical technique provides information about the positions of ¹H or ¹³C atoms in a molecule?
Nuclear magnetic resonance (NMR) spectroscopy
NMR identifies chemical environments of nuclei in organic compounds.
Why does ¹³C NMR give simpler spectra than ¹H NMR?
Fewer signals and no coupling
¹³C atoms are less abundant and coupling with ¹H is often decoupled.
Fill in the blank:
In NMR spectroscopy, chemical shifts are recorded on the ______ scale.
δ
The δ scale measures resonance relative to TMS in ppm.
True or False:
The chemical shift of a nucleus depends on its molecular environment.
True
Electron density around the nucleus affects the magnetic shielding.
What does the integration of ¹H NMR signals indicate?
Relative number of protons
The area under a peak is proportional to the number of equivalent hydrogens.
True or False:
NMR samples are typically dissolved in deuterated solvents to avoid interference from ¹H.
True
Solvents such as CDCl₃ or CCl₄ are commonly used.
Fill in the blank:
Tetramethylsilane (TMS) is used as a standard because it produces a single signal at δ = ______.
0
It is inert, volatile and gives a sharp reference peak.
How can ¹H NMR spectra be used to deduce the number of protons in different environments?
Integration and chemical shift
Each unique hydrogen gives a peak; integration shows relative numbers.
True or False:
The n+1 rule predicts the number of peaks due to spin–spin splitting in ¹H NMR.
True
A proton with n adjacent non-equivalent protons splits into n+1 peaks.
Fill in the blank:
In aliphatic compounds, spin–spin splitting can produce doublets, triplets and ______.
quartets
These arise from coupling with neighbouring protons.
Why is TMS suitable as an NMR standard?
- Chemically inert and produces a single signal
- It is non-toxic
- It has a low boiling point (26°C) and so can be easily removed from the sample afterwards
Its δ = 0 peak provides a reference point for chemical shifts.
How can ¹H and ¹³C NMR data be used to suggest molecular structures?
By comparing chemical shifts and splitting
Peaks, integration and multiplicity reveal the types and connectivity of hydrogens and carbons.
When would you use CCl4 as a solvent?
When analysing non polar compounds.
When would you use deuterated solvents in NMR?
When analysing polar compounds.
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3.1.1 Atomic structure50
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3.1.2 Amount of substance47
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3.1.3 Bonding90
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3.1.4 Energetics62
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3.1.5 Kinetics55
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3.1.6 Equilibria & Kc24
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3.1.7 Redox equations17
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3.1.8 Thermodynamics27
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3.1.9 Rate equations24
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3.1.10 Kp12
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3.1.11 Electrode potentials46
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3.1.12 Acids and bases69
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3.2.1 Periodicity22
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3.2.2 Group 2 metals24
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3.2.3 Group 7 (halogens)31
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3.2.4 Period 3 oxides35
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3.2.5 Transition metals95
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3.2.6 Ions in aqueous solution39
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3.3.1 Intro to organic chemistry42
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3.3.2 Alkanes49
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3.3.3 Halogenoalkanes36
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3.3.4 Alkenes36
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3.3.5 Alcohols43
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3.3.6 Organic analysis36
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3.3.7 Optical isomerism12
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3.3.8 Aldehydes & ketones20
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3.3.9 Carboxylic acids & derivatives25
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3.3.10 Aromatic chemistry29
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3.3.11 Amines41
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3.3.12 Polymers24
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3.3.13 Amino acids, proteins, DNA61
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3.3.14 Organic synthesis12
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3.3.15 NMR spectroscopy14
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3.3.16 Chromatography12
