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CHM 504
Nuclear Magnetic Resonance Spectroscopy
NMR spectrometer
Information from 1H NMR Spectrum
1. Number of different kinds of equivalent atoms.
– Number of different signals
2. Number of equivalent atoms of each kind (only in 1H
NMR; more difficult in 13C NMR).
– Integration (area under each signal)
3. Chemical environment of each kind of atom (functional
groups)
– Chemical shift
4. Connectivity (nearby atoms).
– Splitting of signals
1H
NMR Spectrum of CH3CO2CH3
Chemical Shift
frequency of signal (Hz)  frequency of TMS (Hz)
 (ppm) 
Spectrometer frequency (MHz)
• Independent of spectrometer used.
• Most 1H signals in the range 0-12 ppm (from right to left)
• Correlates with chemical environment (functional groups)
Regions of 1H NMR spectrum
1H
Chemical shifts and functional groups
 (ppm)
Type of H
0.5 – 1.5
1.5 – 2.5
2.5 – 3.0
Y = O, N, Cl, Br
2.5 – 4.5
4.5 – 6.5
6.5 – 9.0
Aromatic H
9.5 – 10.5
Aldehyde H
1.5 – 6.0
Alcohol OH
9.5 - 12
Carboxylic acid OH
Integration
• “Integration” is the determination of the area under each
peak.
• The spectrometer measures this in arbitrary units and
displays it as a step graph.
• Area under a peak ∝ number of H atoms giving rise to
that peak.
• Thus the “Integral” allows you to deduce how many
equivalent H atoms of each kind are present.
• Does not work for 13C NMR.
1H
NMR Spectrum of Methyl 2,2Dimethylpropanoate
Signal splitting
• Coupling to neighbouring H nuclei (2-3 bonds away, i.e.,
attached to same or adjacent C atoms).
• Neighbouring H nuclei may be in +1/2 or -1/2 spin state
(approx. 1:1)
• Affects the effective magnetic field felt by the nucleus.
Beff = B0 – Bshielding ± Bneighbouring
• Signal is split into two (doublet) in 1:1 ratio.
• Implication: 1 neighbouring H.
Signal splitting (contd)
• Bneighbouring is independent of B0. Hence, the split signals
are separated by the same frequency difference
regardless of the spectrometer used.
• This frequency difference is called the coupling constant,
J (typically 1-18 Hz).
• Splitting is mutual. If nucleus A splits the signal of
nucleus B, then vice versa with the same J.
• NO SPLITTING IS OBSERVED BETWEEN
EQUIVALENT NUCLEI.
• Thus, coupling is observed across 2 bonds (H’s attached
to the same C) only if they are non-equivalent.
Splitting patterns
No. of equivalent
Multiplicity
splitting H’s
1
Doublet (d)
2
Triplet (t)
3
Quartet (q)
4
5
6
Quintet
Sextet
Septet
Peak intensity ratio
1:1
1:2:1
1:3:3:1
1:4:6:4:1
1:5:10:10:5:1
1:6:15:20:15:6:1
1H
NMR spectrum of CH3CH2Br
Interpretation
• A typical pattern for a CH3CH2 (ethyl) group.
• The 3 H triplet implies a CH3 with a neighbouring CH2
group.
• The 2 H quartet implies a CH2 with a neighbouring CH3
group.
1H
NMR Spectrum of (CH3)2CHI
Interpretation
• A typical pattern for a (CH3)2CH (isopropyl) group.
• The 6 H doublet implies 2 CH3 groups with a
neighbouring CH (i.e., attached to a CH).
• The 1 H septet implies a CH with 2 neighbouring CH3
groups.
1H
NMR Spectrum of toluene
Information from 13C NMR Spectrum
1. Number of different kinds of equivalent atoms.
– Number of different signals
2. . Chemical environment of each kind of atom (functional
groups)
– Chemical shift
13C
Chemical shifts and functional groups
 (ppm)
Type of H
0 - 60
Alkyl C
30 - 80
C–Y (Y = O, N, Cl, Br)
65 - 85
Alkyne C
100 - 150
Alkene C
110 - 160
Aromatic C
160 - 185
Carbonyl C (carboxylic acids, esters, amides)
180 - 220
Carbonyl C (aldehydes, ketones)
13C
NMR spectrum of 6-methyl-5-hepten-2-ol