Interpreting IR and NMR spectra - CSC-year-12

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Interpreting IR and NMR spectra
Interpreting IR
The Fingerprint Region
• The fingerprint region is the region between
500-1500cm-1. It is very difficult to identify
specific IR absorbance in this region. However
it is very important in identifying between
structural isomers. as shown in the following
slides
Interpreting IR
Propan-1-ol
Propan-2-ol
Interpreting IR
Bond
Wave Number (cm-1)
C-Cl
700 – 800
C-C
750-1100
variable
C-O
1000-1300
strong
C=C
1610-1680
variable
C=O
1670-1750
strong
O-H (acids)
2500-3300
broad, variable
C-H
2850-3300
strong
O-H (alcohols)
3200-3550
broad, strong
N-H (primary amines)
3350-3500
moderate
Type of Trough
IR Examples
IR Examples
IR Examples
IR Examples
IR Examples
IR Examples
IR Examples
IR Examples
IR Examples
IR Examples
Interpreting NMR
Low Resolution Proton NMR
There are three key pieces of information that
can be gained from low res proton NMR
• number of proton environment (number of
peaks on the spectra)
• peak ratio (the ratio of hydrogens in the
groups)
• chemical shift (the movement caused by the
type of group present)
Example of Low Resolution NMR
Which of the following compounds
relates to the low res NMR below
• Number of peaks = 3
therefore 3 proton
environments (not
methyl ethanoate)
• Peak Ratio 1:2:3 (again
not methyl ethanoate)
• Peak at ~12 carboxylic
acid - the compound is
propanoic acid
Interpreting NMR
High Resolution NMR
High resolution NMR gives us the same information
as low res NMR but it also tells us the number of
hydrogens on adjacent carbons.
The number of peaks shown on a high resolution
NMR is one more than the number of hydrogens
on adjacent carbons.
The exception to this is when all adjacent hydrogens
are equivalent then there is no splitting
Interpreting NMR
• Carbon 13 NMR
• Carbon 13 NMR gives us less information than
proton NMR, however it is often used
alongside proton NMR to identify compounds
that have similar proton NMR spectra.
• Carbon 13 NMR identifies types of Carbons
based on chemical shifts.
Example of NMR spectra
Example of NMR spectra
More NMR examples
• http://www.chem.ucla.edu/~webspectra/
• http://home.clara.net/rod.beavon/spectra.ht
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