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www.chemsheets.co.uk A2 032 17-Jul-12
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Protons and neutrons can be regarded as spinning about
their axis.
In many atoms these spins are paired against each other
and so the nucleus has no overall spin (e.g.12
C). In some atoms (e.g. 1H and 13C) the nucleus has an
overall spin.
A nucleus that spins generates a magnetic
field.
The direction of the magnetic field depends
which way the nucleus spins.
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Usually the two possible spin states of the nucleus have
the same amount of energy.
However, in a magnetic field, the two spin states have
different energies.
Energy Applied
magnetic
field
Magnetic field in
same direction as
applied field
Magnetic field
opposed to
applied field
Energy gap corresponds tofrequency of radiowaves
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butanone
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In a spectrum, there is one signal for each set of
equivalent H atoms.
The intensity of each signal being proportional to the
number of equivalent H atoms it represents.
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CH3 CH CH2 CH3
Br
CH3 CH CH2 CH2 CH3
Br
CH3 CH2 CH3 2 sets of equivalent Hs: ratio 6:2 (3:1)
CH3 C
CH3
CH2
OH
CH3
4 sets of equivalent Hs: ratio 3:1:2:3
5 sets of equivalent Hs: ratio 3:1:2:2:3
4 sets of equivalent Hs: ratio 6:1:2:3
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For each of the following compounds, predict the
number of signals and the relative intensity of the
signals.
a) methylpropene
b) propene
c) 2-chloropropane
d) propanone
e) methylamine
f) ethyl propanoate
g) 1,2-dibromopropane
h) dimethylethyl
propanoate
i) but-2-ene
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2 signals: ratio 6:2 (3:1)
C CH3
CH3
O
CH CH3CH3
Cl
CH2 C CH3
CH3
CH2 CH CH3
3 signals: ratio 2:1:3
2 signals: ratio 6:1
1 signal
CH3 CH2 C
O
O CH2 CH3
CH3
NH2
2 signals: ratio 3:2
4 signals: ratio 3:2:2:3
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3 signals: ratio 2:1:3
2 signals: ratio 6:2 (3:1)
CH CH3CH2
BrBr
CH3 CH2 C
O
O C CH3
CH3
CH33 signals: ratio 3:2:9
CH CHCH3 CH3
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Samples are dissolved in solvents free of1H atoms, e.g.
CCl4, CDCl3.
CH3
Si CH3
CH3
CH3
A small amount of TMS
(tetramethylsilane) is added to calibratethe spectrum.
It is used because:
its signal is away from all the others
it only gives one signal
it is non-toxic
it is inert
it has a low boiling point so is easy to remove www.chemsheets.co.uk A2 032 17-Jul-12
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8 7 6 5 4 3 2 1
chemical shift
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8 7 6 5 4 3 2 1
chemical shift
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The spectra are recorded on a scale known as thechemical shift (), which is how much the field is shifted
from the field for TMS compared to the field for TMS.
= Field for TMS - Field measured x 106
Field for TMS
The is a measure in parts per million (ppm) of how far the
magnetic field required for absorption is shifted away from
that for TMS.
012345678910
chemical shift (ppm)
The depends on what other atoms/groups are near the H
more electronegative groups gives a greater shift. www.chemsheets.co.uk A2 032 17-Jul-12
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Data from AQA datasheet
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For each of the following compounds, predict the
number of signals and the relative intensity of the
signals.
a) but-1-ene
b) 1,2-dichloropropane
c) propanal
d) 2-methylpropan-2-ol
e) pentane
f) ethyl methylpropanoate
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a) but-1-ene
b) 1,2-dichloropropane
c) propanal
d) 2-methylpropan-2-ol
e) Pentane
f) ethyl methylpropanoate
CH3 CH2 CH CH2
CH2 CH CH3
Cl Cl
CH3 CH2 C
O
H
CH3 C CH3
OH
CH3
CH3
CH2
CH2
CH3
CH2
CH3 CH C
O
O
CH3
CH2 CH3
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N b f i l
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Number of signals
Relative size
Chemical shift
CH3 CH2 C
O
H
CH3 CH C
O
O
CH3
CH2 CH3
a) propanal
b) ethyl methylpropanoate
Data from AQA datasheet
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Coupling / Splitting / Multiplicity
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CH3 CH2 C CH3
O
0 H next door
singlet (s)
1 H next doordoublet (d)
2 H next doortriplet (t)
3 H next doorquartet (q)
more H next doormultiplet (m)
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signal singlet doublet triplet quartet
appearance
number of lines 1 2 3 4
number of Hsnext door
0 1 2 3
relative size 1:1 1:2:1 1:3:3:1
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CH3 CH C
O
O
CH3
CH2 CH3
C CH CH3
Br
CH3
Br
Br
CH3 CH2 CH3
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CH3
CH2
CH2
CH3
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CH3 CH2 CH2 CH3CH2
CH3 C
O
CH2CH2 C
O
CH3
CH3 C
O
CH2CH2 C
O
CH2 CH3
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CH3 CH2 OH
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But you dont couple to
Hs that are equivalent
Hs on Os
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Number of signals
Position of signals
Relative intensities
Splitting
how many different sets of
equivalent H atoms there are
information about chemicalenvironment of H atom
gives ratio of H atoms for peaks
how many H atoms on adjacent C
atoms
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For each of the following compounds, predict the
number of signals, the relative intensity of the
signals, and the multiplicity of each signal.
a) methylpropene
b) propene
c) 2-chloropropane
d) propanone
e) methylamine
f) ethyl propanoate
g) 1,2-dibromopropane
h) dimethylethyl
propanoate
i) but-2-ene
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2 signals: ratio 6 : 2 (3 :1)
s s
C CH3CH3
O
CH CH3CH3
Cl
CH2 C CH3
CH3
CH2
CH CH3
3 signals: ratio 2 : 1 : 3
d m d
2 signals: ratio 6 : 1
d m
1 signal
CH3 CH2 C
O
O CH2 CH3
CH3
NH2
2 signals: ratio 3 : 2
t q
4 signals: ratio 3 : 2 : 2 : 3
t q q t
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3 signals: ratio 2 : 1 : 3
d m d
2 signals: ratio 6 : 2 (3 :1) d q
CH CH3CH2
BrBr
CH3 CH2 C
O
O C CH3
CH3
CH33 signals: ratio 3 : 2 : 9
t q s
CH CHCH3 CH3
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Number of signals
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Number of signals
Relative size
Chemical shift
Multiplicity
a) 1,2-dichloropropane
b) but-1-ene
CH3 CH2 CH CH2
CH2 CH CH3
Cl Cl
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13C NMR spectra are often simpler than 1H NMR spectra.
They give a lot of valuable information about the chemicalenvironment of C atoms (e.g. the difference between Catoms in C=O, C-N, C N, C-C, C=C, etc.).
There is one signal for each set of equivalent C atoms.
There is no coupling (unlike 1H NMR).
The size of signal is not relative to the number of equivalent
C atoms (unlike H atoms in
1
H NMR). As in 1H NMR, the chemical shift (d) is measured relative to
TMS.
Although deuterated solvents are usually used, there will be
a signal for any C atoms in the solvent. www.chemsheets.co.uk A2 032 17-Jul-12
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Data from AQA datasheet
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Data from AQA datasheet
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