Ch_322b_18.08

Ch_322b_18.08 - Summary R C OH O = 1710 cm-1 Ar C OH O...

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Spectroscopic Properties of Acyl Compounds Infrared Spectroscopy Acyl compounds show a characteristic absorption in the infrared region due to the C=O stretch . This band is typically very strong and easy to see in an infared spectrum. The exact location of the band (frequency) depends on the functional group (acid, ester, amide, etc.), and the electronic structure of the compound. Amides with N-H show sharp bands between 3200 and 3400 cm -1 in addition to the C=O stretch between 1650-1690 cm -1 . Esters show only the C=O stretch somewhere between 1715-1750 cm -1 . Carboxylic acids are readily identified by the C=O stretch near 1700 cm -1 and a broad O-H stretch between 2400-3500 cm -1 .
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Influence of the Electronic Structure Conjugation between an alkene or aromatic ring and the carbonyl group in acids and esters shifts the C=O stretch to lower frequencies.
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Unformatted text preview: Summary R C OH O = 1710 cm-1 Ar C OH O 1680-1690 cm-1-OH 2400-3500 cm-1 R C OR' O Ar C OR' O ~1735 cm-1 1720-1725 cm-1 carboxylic acids esters R C NH 2 O R C NHR' O R C NR' 2 O 1650-1690 cm-1-N-H 3200-3400 cm-1 (two bands for NH 2 ) amides Examples propanoic acid CH 3 CH 2 COH O = ethyl acetate CH 3 COCH 2 CH 3 O = 2,2-dimethylpropanamide (CH 3 ) 3 CCNH 2 O = N,N-dimethylpropanamide CH 3 CH 2 CN(CH 3 ) 2 O Proton NMR Spectroscopy example: propanoic acid CH 3 CH 2 COH O = The acidic proton of a carboxylic acid is highly deshielded (it is highly electropositive), and appears far downfield beyond the aromatic H region, often in the range ! 10-12. The chemical shifts, splitting patterns, and relative intensities of the other H resonances provide detailed structural information, as discussed earlier....
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This note was uploaded on 10/20/2009 for the course CHEM 322BL at USC.

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Ch_322b_18.08 - Summary R C OH O = 1710 cm-1 Ar C OH O...

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