How can use IR spectra to distinguish b/w various carboxylic acids.?
I know how to identify carboxylic acids via IR but not how to further distinguish between carboxylic acids. I am working on an unknowns project and one component is indemnifying a carboxylic acid and one of the methods is IR. So for example are there any distinguishing features between 2-Methylbenzoic acid, 3-Methylbenzoic acis, benzoic acid and 2-benzoylbenzoic acid?
Thank you for your help! I'm always a little confused by IR.
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The region between 2000 and 1667 cm^-1 is an overtone region that has specific band structure based on substitution pattern of the ring, so a 1,2-disubstituted aromatic can be distinguished from a 1,3-disubstitued aromatic by looking at that region:
http://www.chemistry.ccsu.edu/glagovich/teaching/3...
That would help distinguish between 2-methylbenzoic acid, 3-methylbenzoic acid, and benzoic acid. However, the presence of the carbonyl band in this region will complicate this.
With 2-benzoylbenzoic acid, the pattern in that overtone region would be the superimposed monosubstituted and disubstituted patterns, but it should be distinguishable by the presence of an ester absorption.
In IR spectrum analysis, one typically uses comparison with reference spectra. Are you allowed to do that for your project? If so, IR spectra are available at the NIST WebBook site:
http://webbook.nist.gov/chemistry/