The C=O stretching frequency
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The C=O stretching frequency. aldehydes and ketones. A summary of the principle infrared bands and their assignments. R is an aliphatic group. Aliphatic Aldehyde. Figure IR-14. Butanal, neat liquid, thin film: CH 3 CH 2 CH 2 CHO. Aliphatic Ketone.

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The C=O stretching frequency

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The c o stretching frequency

The C=O stretching frequency

aldehydes and ketones


The c o stretching frequency

A summary of the principle infrared bands and their assignments. R is an aliphatic group.


The c o stretching frequency

Aliphatic Aldehyde

Figure IR-14. Butanal, neat liquid, thin film: CH3CH2CH2CHO


The c o stretching frequency

Aliphatic Ketone

Figure IR-35. 5-Hexene-2-one, neat liquid: CH2=CH2CH2CH2COCH3


The c o stretching frequency

The C=O stretching frequency

esters


The c o stretching frequency

A summary of the principle infrared bands and their assignments. R is an aliphatic group.


The c o stretching frequency

Aliphatic Ester

Figure IR-33. Methyl acetate in 0.1 mm NaCl cells: CH3CO2CH3


The c o stretching frequency

neat

CCl4


The c o stretching frequency

Aliphatic Ester

Figure IR-34. Vapor and liquid spectra of ethyl n-hexanoate: CH3CH2CH2CH2CH2CO2CH2CH3


The c o stretching frequency

The C=O stretching frequency

aliphatic acids


The c o stretching frequency

A summary of the principle infrared bands and their assignments. R is an aliphatic group.


The c o stretching frequency

Aliphatic Acid

Figure IR-26. The liquid,

vapor and CCl4 soln

spectra of hexanoic acid:

CH3(CH2)4 CO2H


The c o stretching frequency

The C=O stretching frequency

aliphatic amides


The c o stretching frequency

A summary of the principle infrared bands and their assignments. R is an aliphatic group.


The c o stretching frequency

KBr pellet

Amide I 

1662 cm-1

Amide II; 1634 cm-1


The c o stretching frequency

Secondary Amide

Figure IR-21. N-Methyl acetamide, neat liquid; thin film: CH3CONHCH3


The c o stretching frequency

Tertiary Amide

Figure IR-23. N,N-Dimethylacetamide, neat liquid; thin film: CH3CON(CH3)2


The c o stretching frequency

The C=O stretching frequency

anhydrides


The c o stretching frequency

A summary of the principle infrared bands and their assignments. R is an aliphatic group.


The c o stretching frequency

Anhydrides

Figure IR-36. Propionic anhydride, neat liquid: CH3CH2CO2COCH2CH3


The c o stretching frequency

The C=O stretching frequency

carboxylates


The c o stretching frequency

A summary of the principle infrared bands and their assignments. R is an aliphatic group.


The c o stretching frequency

C=O in an acid 1700 cm-1;C-O-C stretch 1300 to 1000 cm-1,

say in ethers  1150 cm-1. Averaging a C=O with a C-O-C results in: (1700 + 1150)/2 = 1425 cm-1. Naively, we would estimate a bond and a half would have a frequency of 1425 cm-1


The c o stretching frequency

1410 cm-1

1560 cm-1

(1560+ 1410)/2 = 1485 cm-1


The c o stretching frequency

The C=C bond stretch


The c o stretching frequency

A summary of the principle infrared bands and their assignments. R is an aliphatic group.


The c o stretching frequency

Figure IR-9. 1-Heptene; neat sample, thin film:

H2C=CH-CH2CH2CH2CH2CH3


The c o stretching frequency

The C=C bond stretch when next to a heteroatom


The c o stretching frequency

A summary of the principle infrared bands and their assignments. R is an aliphatic group.


The c o stretching frequency

Figure IR-40. 2,5-Dimethoxy2,5-dihydrofuran, neat liquid:


The c o stretching frequency

Figure IR-41. 2,3-Dihydrofuran, neat liquid:


The c o stretching frequency

The cumulative C=C bond stretch


The c o stretching frequency

The NO2 stretching frequency


The c o stretching frequency

A summary of the principle infrared bands and their assignments. R is an aliphatic group.


The c o stretching frequency

Aromatic Rings

Ring breathing motions

1600-1585

1500-1400

Both often appear as doublets


The c o stretching frequency

Benzene, neat, thin film:


The c o stretching frequency

4-Chloro-2-nitrophenol, KBr pellet:


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