24/03/2016
Draw the displayed formula
of ethanol
What would we see in an IR
and in the mass spec for
ethanol?
24/03/2016
Key words
• Odd
• Radio
• CDCl3
• Spin
• TMS
• Magnetic field
24/03/2016
So what is NMR?
• A sample of the compound is spun in a magnetic
field
• hydrogen atoms in different environments
respond differently to the field
•each different environment of hydrogen
produces a signal in a different position
•the area under each peak / signal is
proportional to the number of hydrogens
•The signal can be split according to how many
H’s are on adjacent atoms
24/03/2016
Look at your displayed
formula for ethanol
Predict how many peaks you
would see in the 1H nmr
24/03/2016
NMR of ethanol
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Low resolution and high resolution
• the signal produced indicates the number of
protons on adjacent carbon atoms
• low resolution nmr gives 1 peak for each
environmentally different group of protons
What do you
notice about
the height of
each peak?
LOW RESOLUTION SPECTRUM OF 1BROMOPROPANE
24/03/2016
Draw displayed formula for the
following and sketch the predicted
nmr you would see
a) propan-1-ol,
b) propan-2-ol,
c) propanone
d) propanal
Can we distinguish
between any of these
compounds based on
low resolution nmr
alone?
24/03/2016
Technical bits and pieces
24/03/2016
Tetramethylsilane (CH3)4Si
PROVIDES THE REFERENCE
SIGNAL
The molecule contains
four methyl groups
attached to a silicon atom
in a tetrahedral
arrangement.
All the hydrogen atoms
are chemically
equivalent.
24/03/2016
What other features should our
reference have?
• non-toxic liquid - SAFE TO USE
• inert - DOESN’T REACT WITH COMPOUND BEING
ANALYSED
• has a low boiling point - CAN BE DISTILLED OFF AND
USED AGAIN
• all the hydrogen atoms are chemically equivalent PRODUCES A SINGLE PEAK
24/03/2016
What other features should our
reference have?
• twelve hydrogens so it produces an intense peak DON’T NEED TO USE MUCH
• signal is outside the range shown by most protons WON’T OBSCURE MAIN SIGNALS
• given the chemical shift of  = 0
• the position of all other signals is measured relative to
TMS
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Chemical shift
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Chemical shift
• each proton type is said to be chemically shifted
relative to a (our) standard (usually TMS)
• the delta () scale is widely used as a means of
reporting chemical shifts

=
Observed chemical shift (Hz) x 106
Spectrometer frequency (Hz)
ppm
(parts per million)
the chemical shift of a proton is constant under the same
conditions (solvent, temperature)
24/03/2016
Approximate
chemical shifts
H
- CX
RO
H
CHO
-COOH
13
12
11
- C-H
TM
S
-C=CH10
9
8
7
6
5
DOWNFIELD ‘deshielding’
The actual
values depend
on the
environment
4
3
2
1
0

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Summary
An nmr spectrum provides several types of
information :number of signal groups
tells you
the number of different proton
environments
Multiplicity tells
you
how many protons are on adjacent
atoms
peak area (integration)
tell you
the number of protons in each
environment
chemical shift tell you
the general environment of the
protons
24/03/2016
Draw displayed formula for the
following and sketch the predicted
nmr you would see
a) propan-1-ol,
b) propan-2-ol,
c) propanone
d) propanal
Can we distinguish
between any of these
compounds based on
low resolution nmr
alone?
24/03/2016
What is high resolution
NMR?
24/03/2016
High resolution gives more complex signals doublets, triplets, quartets, multiplets
HIGH RESOLUTION SPECTRUM OF 1BROMOPROPANE
The broad
peaks are
split into
sharper
signals
The splitting pattern depends on the number of hydrogen atoms on
adjacent atoms
24/03/2016
Challenge – can you draw the
HIGH resolution NMR for
a) propan-1-ol,
b) propan-2-ol,
c) propanone
d) propanal?