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

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