Section 20 21 spectroscopic analysis of carboxylic acid derivatives
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Section 20.21 Spectroscopic Analysis of Carboxylic Acid Derivatives. O. O. O. O. O. CH 3 CCl. CH 3 COCCH 3. CH 3 COCH 3. CH 3 CNH 2. Infrared Spectroscopy. C=O stretching frequency depends on whether the compound is an acyl chloride, anhydride, ester, or amide.

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Section 20.21 Spectroscopic Analysis of Carboxylic Acid Derivatives

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Section 20 21 spectroscopic analysis of carboxylic acid derivatives

Section 20.21Spectroscopic Analysis ofCarboxylic Acid Derivatives


Infrared spectroscopy

O

O

O

O

O

CH3CCl

CH3COCCH3

CH3COCH3

CH3CNH2

Infrared Spectroscopy

C=O stretching frequency depends on whether thecompound is an acyl chloride, anhydride, ester, oramide.

C=O stretching frequency n

1822 cm-1

1748

and

1815 cm-1

1736 cm-1

1694 cm-1


Infrared spectroscopy1

O

O

CH3COCCH3

Infrared Spectroscopy

Anhydrides have two peaks due to C=O stretching. One results from symmetrical stretching of the C=Ounit, the other from an antisymmetrical stretch.

C=O stretching frequency n

1748

and

1815 cm-1


Infrared spectroscopy2

Infrared Spectroscopy

Nitriles are readily identified by absorption due to carbon-nitrogen triple bond stretching in the 2210-2260 cm-1 region.


1 h nmr

O

O

RCOR'

R'COR

O

O

C

C

C

H

H

1H NMR

1H NMR readily distinguishes between isomericesters of the type:

and

is less shielded than


1 h nmr1

O

O

CH3COCH2CH3

1H NMR

For example:

CH3CH2COCH3

and

Both have a triplet-quartet pattern for an ethylgroup and a methyl singlet. They can beidentified, however, on the basis of chemicalshifts.


Figure 20 9

O

O

CH3COCH2CH3

5.0

4.0

3.0

2.0

1.0

0

5.0

4.0

3.0

2.0

1.0

0

Figure 20.9

CH3CH2COCH3

Chemical shift (d, ppm)


13 c nmr

13C NMR

Carbonyl carbon is at low field (d 160-180 ppm), but not as deshielded as the carbonyl carbon of an aldehyde or ketone (d 190-215 ppm).

The carbon of a CN group appears near d 120ppm.


Uv vis

O

O

O

O

O

CH3CCl

CH3COCCH3

CH3COCH3

CH3CNH2

UV-VIS

nÆp* absorption: lmax

235 nm

225 nm

207 nm

214 nm


Mass spectrometry

••

•+

O

O

••

••

+

RC

RCX

RCX

O

X

••

••

••

••

Mass Spectrometry

Most carboxylic acid derivatives give a prominentpeak for an acylium ion derived by thefragmentation shown.

+


Mass spectrometry1

••

•+

O

O

••

••

+

••

O

RCNR'2

RCNR'2

NR'2

R

C

••

••

••

Mass Spectrometry

Amides, however, cleave in the direction that givesa nitrogen-stabilized cation.

+


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