SPECTROSCOPY

7.53

TABLE 7.23 Absorption Frequencies of Carbonyl Bands (Continued)

Groups

Band, cm 1

Remarks

Imides 9CO9N9CO9

Cyclic six-ring

ca 1710 and

Shift of 15 cm 1 with , unsaturation

ca 1700

Cyclic five-ring

ca 1770 and

ca 1700

Ureas N9CO9N

RNHCONHR

ca 1660

Six-ring

ca 1640

Five-ring

ca 1720

Urethanes R9O9CO9N

1740–1690

Also shows amide II band when nonsubsti-

tuted on N

Thioesters and Acids

RCO9S9R

RCOSH

ca 1720

, -Unsaturated or aryl acid or ester shifted

about 25 cm 1

RCOS9alkyl

ca 1690

RCOS9aryl

ca 1710

7.54

SECTION 7

TABLE 7.24

Absorption Frequencies of Other Double Bonds

Abbreviations Used in the Table

m, moderately strong

vs, very strong

m–s, moderate to strong

w, weak

var, of variable strength

Group

Band, cm 1

Remarks

Alkenes C "C

Nonconjugated

1680–

1620

(w–m)

May be very weak if symmetrically

substituted

Conjugated with aromatic ring

1640–

1610

(m)

More intense than with unconju-

gated double bonds

Internal (ring)

3060–

2995

(m)

Highest frequencies for smallest

ring

Carbons:

n 3

ca 1665 (w–m)

n 4

ca 1565 (w–m)

n 5

ca 1610 (w–m)

1370–

1340

(s)

Characteristic

n 6

1650–

1645

(w–m)

Exocyclic C"C(CH2)n n 2

1780–

1730

(m)

n 3

ca 1680 (m)

n 4

1655–

1650

(m)

Fulvene

1645–

1630

(m)

1370–

1340

(s)

790–

765 (s)

Dienes, trienes, etc.

1650 (s)

Lower-frequency band usually more

and 1600 (s)

intense and may hide or overlap

the higher-frequency band

, -Unsaturated carbonyl compounds

1640–

1590

(m)

Usually much weaker than the

C"O band

Enol esters, enol ethers, and

enamines

1700–

1650

(s)

Imines, oximes, and amidines

C "N 9

Imines and oximes

Aliphatic

1690–

1640

(w)

, -Unsaturated and aromatic

1650–

1620

(m)

Conjugated cyclic systems

1660–

1480

(var)

960–

930 (s)

NO stretching of oximes

Imino ethers

9O9C"N9

1690–

1640

(var)

Usually a strong doublet

SPECTROSCOPY

7.55

Group

Band, cm 1

Remarks

Imino thioethers

9S9C"N"

1640–1605

(var)

Imine oxides

1620–1550

(s)

C "N 9O

Amidines

N 9C "N 9

1685–1580

(var)

Benzamidines Aryl9C"N9N

1630–1590

Guanidine

N 9C "N 9

1725–1625

(s)

N

Azines

C "N 9N "C

1670–1600

Hydrazoketones

9CO9C"N9N

1600–1530

(vs)

Azo compounds 9N"N9

Azo 9N"N9

Aliphatic

ca 1575 (var)

Very weak or inactive

Aromatic

cis

ca 1510 (w)

trans

1440–1410 (w)

Azoxy 9N "N 9

O

Aliphatic

1590–1495 (m–s)

1345–1285 (m–s)

Aromatic

1480–1450 (m–s)

1340–1315 (m–s)

Azothio

1465–1445 (w)

9N"N 9S9

1070–1055 (w)

Nitro compounds N"O

Nitro C9NO2

Aliphatic

ca 1560 (s)

The two bands are due to asymmet-

1385–1350 (s)

rical and symmetrical stretching

of the N"O bond. Electron-

withdrawing substituents adjacent

to nitro group increase the fre-

quency of the asymmetrical band

and decrease that of the symmet-

rical frequency.

7.56

SECTION 7

TABLE 7.24

Absorption Frequencies of Other Double Bonds (Continued)

Group

Band, cm 1

Remarks

Nitro compounds N"O (continued)

Nitro C9NO2 (continued)

Aromatic

1570–

1485

(s)

See above remark; also bulky

1380–

1320

(s)

orthosubstituents shift band to

higher frequencies. Strong H

bonding shifts frequency to lower

end of range.

865–

835

(s)

Strong and sometimes at ca 750

cm 1

580–

520

(var)

, -Unsaturated

1530–

1510

(s)

Nitroalkenes

1360–

1335

(s)

Nitrates

9O9NO2

1650–

1625

(vs)

1285–

1275

(vs)

870–

855

(vs)

760–

755

(w–m)

710–

695

(w–m)

Nitramines

N 9NO2

1630–

1550

(s)

1300–

1250

(s)

Nitrates

9O9N"O

1680–

1610

(vs)

Two bands

815–

750

(s)

Trans form

850–

810

(s)

Cis form

690–

615

(s)

Thionitrites 9S9N"O

730–

685

(m–s)

Nitroso

C 9N "O

1600–

1500

(s)

N9N"O

Aliphatic

1530–

1495

(m–s)

Aromatic

1480–

1450

(m–s)

1335–

1315

(m–s)

Nitrogen oxides

N :O

Pyridine

1320–

1230

(m–s)

1190–

1150

(m–s)

Pyrazine

1380–

1280

(m–s)

Affected by ring substituents

1040–

990

(m–s)

ca 850 (m)