IR Frequencies

SEQ CHAPTER \h \r 1Characteristic Infrared Absorption Frequencies a_________________________________________________________________________

Bond

Compound Type

Frequency range, cm)1_________________________________________________________________________

HydrocarbonsC)H stretchingAlkanes

2840)3000

)CH3

2872 & 2962 (s)

)CH2

2853 & 2926

)CH (3E)

2890 (w)

)CH2 & )CH (cyclic)

2990)3100

Alkyl

2853)2962 (m)s)

Alkenes

3010)3095 (m)

Alkynes (RC/CH)

3267)3333 (s)

Aromatic

3000)3100

C)H bending

Alkanes

)CH3

1375 & 1450

)CH2

1465 & 1150)1350

)CH2 (straight chain >7 C)

720

)CH(CH3)2

1365)1370, 1380)1385 (s, d), & 919)922 (w)

)C(CH3)3

1370 (s), 1385)1395 (m), & 926)932 (w)

cyclohexane

1452

cyclopentane

1455

cyclopropane

1442

Alkenes

cis disubstituted, vinyl

1416

Alkynes

(RC/CH, HC/CH)

610)700 (s, b) & 1220)1370 (w, b)

C)H

Alkenes

650)1000 (s)

out)of)plane RCH=CH2

905)915 (s) & 985)995(s)

bending

R2C=CH2

885)895 (s)

RCH=CHR (cis)

665)730 (s)

RCH=CHR (trans)

960)980 (s)

R2C=CHR

790)840 (m)

Allenes =CH2

850

Aromatic

675)900 (s)

monosubstituted

690)710 (s) & 730)770(s)

o)disubstituted

735)770 (s)

m)disubstituted

680)725 (s) & 750)810(s)

p)disubstituted

800)840 (s)

C)H in)plane

Alkenes

bending

=CH2

1416

Aromatic

1000)1300

Characteristic Infrared Absorption Frequencies (contd)

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Bond

Compound Type


HydrocarbonscontinuedC=C

Alkenes

1620)1680 (v)

stretching

unconjugated

1640)1667 (m, w)

RCH=CH2

1638)1648

R2C=CH2

1648)1658 (m)

RCH=CHR (cis)

1626)1662 (v)

RCH=CHR (trans)

1668)1678 (v)

R2C=CHR

1665)1675 (m)

R2C=CR2

1665)1675 (w)

)CH=CF2

1754

)CF=CF2

1786

cyclopropene

1641

cyclobutene

1566

")substituted cyclobutene1641

conjugated

1600 & 1650

conjugated with an

aromatic ring

1625

cumulated

1900)2000

Aromatic

1400)1500 & 1585)1600

C/C stretchingAlkynes

2100)2260 (w)

symmetrical

no band

RC/CH

2100)2140

RC/CR (unsymmetrical)

2190)2260

Characteristic Infrared Absorption Frequencies (contd)_________________________________________________________________________

Bond

Compound Type


Alcohols and PhenolsO)H stretchingAlcohols, Phenols (vapor phase or

very dilute solution)

3584)3650 (s)

Alcohols, Phenols

3200)3550 (b, s)

C)O

Alcohols

1000)1260 (s)

stretching

1E

")unsaturated and/or

")branched

6)membered)

1650

J)Lactams

1700)1750

$)Lactams

1730)1760

N)H bending

Amides

1515)1650 & 666)800 (b, m)

1E (mulls and pellets)

1620)1655

(dilute solutions)

1590)1620

2E acyclic

(solid samples)

1515)1570

(dilute solutions)

1510)1550

Lactams

700)800 (b)

C)N stretching1E Amides

1400


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Bond

Compound Type


Amines and Salts of AminesN)H stretchingAmines

3300)3500 (m)

1E

3300)3500 (two bands)

(dilute solutions)

3400 (w) & 3500 (w) (two bands)

aliphatic (neat)

3250)3330 & 3330)3400

2E

3310)3350 (w) (one band)

3E

3300)3500 (no bands)

Amine salts

ammonium

3030)3300 (b, s) & 1709)2000

1E

2800)3000 (b, s) & 2000)2800 (m)

2E

2700)3000 (s) & 2000 (m)

3E

2250)2700

4E

no bands

N)H bending

Amines

1E

1580)1650 (m or s)

2E aliphatic

undetected

aromatic

1515

1E, 2E (liquid samples)

666)909

Amine salts

ammonium

1429 (b, s)

1E

1504)1550 & 1575)1600

2E

1560)1620

C)N stretchingAmines

1E, 2E, 3E aliphatic

1020)1250 (m, w)

1E aromatic

1250)1340 (s)

2E aromatic

1280)1350 (s)

3E aromatic

1310)1360 (s)


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Bond

Compound Type


Amino Acids and Salts of Amino Acids

N)H stretchingFree 1E amino acids

2600)3100 (b, s)

Hydrochloride salts of amino acids2380)3333 (s)

Sodium salts of amino acids

3200)3400

N)H bending

Free 1E amino acids

1485)1550 (s),

1610)1660 (w) & 2000)2222 (m)

Hydrochloride salts of amino acids1481)1550 (s) & 1590)1610 (w)

C=O stretchingFree 1E amino acid

1590)1600 (s) & 1400 (w)

Sodium salts of amino acids

1590)1600 (s) & 1400 (w)

O)C4O stretchingHydrochloride salts of amino acids1190)1220 (s)

C=O stretching")Amino acid hydrochlorides1730)1755 (s)

Other amino acid hydrochlorides1700)1730 (s)

O)H stretchingHydrochloride salts of amino acids2380)3333 (s)

Compounds with C/N, C=N, )N=C=O, )N=C=S Groups

C/N stretchingNitriles

2220)2260 (m)

aliphatic

2240)2260

aromatic, conjugated

2222)2240

Isocyanides, isocyanates,

thiocyanates, isothiocyanates2000)2273

C=N stretchingImines, oximes, thiazoles,

iminocarbonates, guanidines1471)1689

Compounds with Nitrogen)Oxygen Bonds

N- -O stretchingNitro compounds

1259)1389 & 1499)1661(s)

nitroalkanes

1372 & 1550

conjugated aliphatic, aromatic1290)1360 & 1500)1550

N)O stretchingNitrates

1255)1300 (s) & 1625)1660 (s)

Nitrites

750)850 (s)

N=O stretchingNitrates

833)870

Nitrites

cis isomer

1610)1625 (s)

trans isomer

1650)1680 (s)

Nitroso compounds, monomeric, tertiary

aliphatic

1539)1585

aromatic

1495)1511

N- -O bendingNitrates

690)763

C)N stretchingNitroaromatics

870


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Bond

Compound Type


Organic Halogen Compounds C)X stretchingChlorides

aliphatic

550)850 (s)

aryl

1089)1096 (s)

Bromides

515)690 (s)

Iodides

500)600 (s)

Fluorides

730)1400 (s)

monofluoroalkanes

1000)1100 (s)

)CF2), )CF3

1120)1350 (s)

aryl

1100)1250 (s)

Organic Sulfur Compounds S)H stretchingAliphatic mercaptans, thiophenols2550)2600 (w)

Thioketos

2415 (b)

C)S stretchingSulfides

600)700 (w)

S)S stretchingDisulfides

400)500 (w)

C=S stretchingThiocarbonyls

1020)1250

Thiobenzophenones

1207)1224

Compounds Containing Sulfur)Oxygen BondsS=O stretchingOrganic sulfoxides

1030)1070 (s)

Sulfones

1120)1160 (s) & 1300)1350 (s)

Sulfonyl chlorides

1177)1204 (s) & 1380)1410 (s)

Sulfonamides

1155)1170 (s) & 1335)1370 (s)

Covalent sulfonates

1168)1195 (s) & 1335)1372 (d, s)

Organic sulfates

1185)1200 (s) & 1380)1415 (s)

Sulfonic acids

1150)1165 (s) & 1342)1350 (s)

Sulfonate salts

1055 (s) & 1175 (s)

N)H stretchingSulfonamides

1E

3247)3300 (s) & 3330)3390 (s)

2E

3265 (s)


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Bond

Compound Type


Silicon Compounds

Si)H stretching

2200

Si)H bending

800)950

SiO)H stretching

3200)3700

Si)O stretching

830)1110 (s)

Si)X stretchingSi)F

800)1000

Si)Cl

below 666

Phosphorus Compounds

P=O stretchingPhosphine oxides

aliphatic

1150

aromatic

1190

Phosphate esters

1250)1299

P)O stretchingP)OH bonds

910)1040 (s)

P)O)P bonds

700 (w), 870)1000 (s)

P)O)C bonds

aliphatic

770)830 (s), 970)1050(s)

aromatic

855)994(s),1160)1260(s)


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Bond

Compound Type


Heteroaromatic Compounds

C)H stretchingPyridines, Pyrazines, Pyrroles,

Furans, Thiophenes

3003)3077

N)H stretchingHeteroaromatics

3220)3500

Pyrroles, Indoles

(dilute solution)

3495

(conc solution)

3400

ring stretchingHeteroaromatics

1300)1600

C)H

Pyridines

out)of)plane 2)substituted

746)752 & 740-781

bending 3)substituted

712)715 & 789)810

4)substituted

709)775 & 794)820

Furans

2)substituted

(CHCl3)

780)835, 884, & 925

(liquid)

725)780, 875)890, & 915)960

(solid)

723)750, 793)821, 860)887, &

906)955

3)substituted (liquid)

741 & 870)885

Thiophenes

2)substituted (CHCl3)

803)843, 853, & 925

3)substituted (liquid)

755

Pyrrole

2)acyl

755 & 740)774

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Abbreviations: s = strong, m = moderate, w = weak, d = doublet, b = broad, v = variable, t = triplet

a Compiled from R. M. Silverstein, F. X. Webster, Spectrometric Identification of Organic Compounds, 6th edition (Wiley, New York, 1998) and T. W. G. Solomons, C. Fryhle Organic Chemistry, 7th edition upgrade (Wiley, New York, 2001).

IR Frequencies

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