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has a strong infrared absorption between 1710 and 1740 cm-1 Alkyl substituents ketone carbonyls have slightly lower stretching frequencies, 1715 ± 7 cm-1,

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IR Ȯ Spectroscopy

Part II

1

Carbonyl - compounds

For simple aldehydes and ketones, the stretching vibration of the carbonyl group has a strong infrared absorption between 1710 and 1740 cm-1.

Alkyl substituents are Electron Donating Groups

Ȯ inductive effect lower the bond strength of C=O 2

Ketones and aldehydes

Gas phase

1727 cm-1

3

Ketones and aldehydes

1740 cm-1

1715 cm-1

4

Ketones and aldehydes Ȯ conjugated systems

Conjugation of C=O bond with a double bond or phenyl ring lowers the stretching frequency. 5

Ketones and aldehydes Ȯ conjugated systems

1685 cm-1

6 Ketones and aldehydes Ȯ influence of EDG and EWG 7 Ketones and aldehydes Ȯ influence of EDG and EWG 8 Ketones and aldehydes Ȯ influence of EDG and EWG Two above isomeric ketones has diffirent absorbtion of C=O group, Please, draw appropiate mesomeric structures to explain observed facts. 9

KetonesȮ ring size

Incorporation of the carbonyl group into a small ring, increase the stretching frequency. 10

Carbonyl compounds

11

Acid chlorides Ȯaliphatic - butyryl chloride

Additional band in C=O region is a result of Fermi resonance of C-Cl and C=O 12

Acid chlorides Ȯaromatic - benzoyl chloride

1775 cm-1 1733cm-1

13

Carboxylic anhydrides

Anhydrides C=O stretch: 2 bands separated by 60 -30 cm-1)

Acyclic anhydrides, 1750 and 1820 cm-1;

6-membered ring, 1750 and 1820;

5-membered ring, 1785 and 1865

14

Carboxylic acid Ȯ hydrogen bonds

Spectrum of carboxylic acid in gas phase Ȯ only monomeric molecules 15

Carboxylic acid Ȯ hydrogen bonds

Spectrum of carboxylic acid in solutionȮ dimeric and monomeric 16

Carboxylic acid Ȯ hydrogen bonds

Spectrum of liquid carboxylic acid (pure substance) Ȯ only dimer is observed 17

Primary Amides

Amide I band Α C=O stretching, Amide II band Έ N-H bending in plane Why the wavenumber of I amide band is usualy below 1700 cm-1 ? 18

Amides bond properites

Conjugation of C=O bond with an EDG : (lone pair, double bond or phenyl ring) lowers the stretching frequency. 19

Secondary Amides

Α NH

3326 cm-1 Α C=O

1638 cm-1

Έ NH (in plane)

1554cm-1

Ν NH (out of plane)

711cm-1 645

One stretching band

Α C-N

1450 cm-1

Ν CH aromatic (out of plane)

711cm-1 645

20

TertiaryAmides

None N-H

stretching band

Overtone C=O

3471 cm-1

Α C=O

1640 cm-1

Α C-N

1428 cm-1

21

Lactams

1Σ & 2Σ-amides, 1510 to 1700 cm-1 (2 bands)

3Σ-amides, 1650ц 15 (one band);

6-membered lactams, 1670 ц 10 (one band)

5-membered lactams, 1700 ц 15 ;

4-membered lactams, 1745 ц 15.

Α C=O

1640 cm-1

non-cyclic amides cyclic amides

Α C=O

1671 cm-1 Α C=O

1666cm-1 Α C=O

1700cm-1

Α C=O

1745 cm-1

22

Lactones

Esters, 1740 +/- 10 cm-1;

6 membered lactone, 1740 +/- 10 cm-1;

5 membered lactone, 1765 +/- 10 cm-1;

4 membered lactone, 1840 +/- 5 cm-1

Α C=O

1749 cm-1

non-cyclic esters cyclic esters

Α C=O

1740cm-1 Α C=O

1775cm-1 Α C=O

1818 cm-1

23

Alkohols Ȯ hydrogen bonds

24

Alcoholic C-O Stretch

Alcohol Type Absorption Range

cm-1 1

Saturated tertiary

Secondary (highly symmetrical)

1205-1124

3 Secondary saturated,

΅-unsaturated or cyclic tertiary

1124-1087

4 Secondary ΅-unsaturated,

Secondary alicyclic five or six- membered ring,

Saturated primary

1085-1050

5 Tertiary, highly ΅-unsaturated

Secondary di-΅-unsaturated

Secondary ΅-unsaturated

Secondary alicyclic seven or eight membered ring

Primary ΅-unsaturated

<1050 25

Alcoholic C-O Stretch

Α C-O

1205 cm-1

Α C-O

1130 cm-1 1160 cm-1

26

Alkyls - Tert-butyl ver isopropyl

cm-1 H)

1480 cm-1

as

CH3 and

s CH2

1390 and 1370 cm-1

s CH3 dublet and cm-1 C-O)

600 -650 cm-1

H) out of planequotesdbs_dbs3.pdfusesText_6