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Interpreting IR and NMR spectra. Interpreting IR. The Fingerprint Region - PowerPoint PPT Presentation
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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 IRBond Wave Number (cm-1) Type of Trough
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
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 NMRThere 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
• 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
Which of the following compounds relates to the low res NMR below
Interpreting NMR
High Resolution NMRHigh 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
m
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