Chemical Sciences: A Manual for CSIR-UGC National Eligibility Test for Lectureship and JRF/Infrared spectroscopy correlation table

In physical chemistry|physical and analytical chemistry, infrared spectroscopy ("IR spectroscopy") is a technique used to identify chemical compounds based on how infrared|infrared radiation is absorbed by the compounds' chemical bonds. This article is an IR spectroscopy correlation table that lists some general absorption peaks for common types of atomic bonds and functional groups. Note that this information is unreferenced, and may not be accurate.

The absorptions in this range do not apply only to bonds in organic molecules. IR spectroscopy is useful when it comes to analysis of inorganic compounds (such as metal complexes or fluoromanganates) as well.

Bond Type of bond Specific type of bond Absorption peak Appearance
C─H alkyl methyl 1260 cm−1 strong
1380 cm−1 weak
2870 cm−1 medium to strong
2960 cm−1 medium to strong
methylene 1470 cm−1 strong
2850 cm−1 medium to strong
2925 cm−1 medium to strong
methine 2890 cm−1 weak
vinyl C═CH2 900 cm−1 strong
2975 cm−1 medium
3080 cm−1 medium
C═CH 3020 cm−1 medium
monosubstituted alkenes 900 cm−1 strong
990 cm−1 strong
cis-disubstituted alkenes 670–700 cm−1 strong
trans-disubstituted alkenes 965 cm−1 strong
trisubstituted alkenes 800–840 cm−1 strong to medium
aromatic benzene/sub. benzene 3070 cm−1 weak
monosubstituted benzene 700–750 cm−1 strong
690–710 cm−1 strong
ortho-disub. benzene 750 cm−1 strong
meta-disub. benzene 750–800 cm−1 strong
860–900 cm−1 strong
para-disub. benzene 800–860 cm−1 strong
alkynes any 3300 cm−1 medium
aldehydes any 2720 cm−1 medium
2820 cm−1
C─C acyclic C─C monosub. alkenes 1645 cm−1 medium
1,1-disub. alkenes 1655 cm−1 medium
cis-1,2-disub. alkenes 1660 cm−1 medium
trans-1,2-disub. alkenes 1675 cm−1 medium
trisub., tetrasub. alkenes 1670 cm−1 weak
conjugated system|conjugated C─C dienes 1600 cm−1 strong
1650 cm−1 strong
with benzene ring 1625 cm−1 strong
with C═O 1600 cm−1 strong
C═C (both sp2) any 1640–1680 cm−1 medium
aromatic C═C any 1450 cm−1 weak to strong (usually 3 or 4)
1500 cm−1
1580 cm−1
1600 cm−1
C≡C terminal alkynes 2100–2140 cm−1 weak
disubst. alkynes 2190–2260 cm−1 very weak (often indisinguishable)
C═O aldehyde/ketone saturated aliph./cyclic 6-membered 1720 cm−1
α,β-unsaturated 1685 cm−1
aromatic ketones 1685 cm−1
cyclic 5-membered 1750 cm−1
cyclic 4-membered 1775 cm−1
aldehydes 1725 cm−1 influence of conjugation (as with ketones)
carboxylic acids/derivates saturated carboxylic acids 1710 cm−1
unsat./aromatic carb. acids 1680–1690 cm−1
esters and lactones 1735 cm−1 influenced by conjugation and ring size (as with ketones)
anhydrides 1760 cm−1
1820 cm−1
acyl halides 1800 cm−1
amides 1650 cm−1 associated amides
carboxylates (salts) 1550–1610 cm−1
amino acid zwitterions 1550–1610 cm−1
O─H alcohols, phenols low concentration 3610–3670 cm−1
high concentration 3200–3400 cm−1 broad
carboxylic acids low concentration 3500–3560 cm−1
high concentration 3000 cm−1 broad
N─H primary amines any 3400–3500 cm−1 strong
1560–1640 cm−1 strong
secondary amines any >3000 cm−1 weak to medium
ammonium ions any 2400–3200 cm−1 multiple broad peaks
C─O alcohols primary 1040–1060 cm−1 strong, broad
secondary ~1100 cm−1 strong
tertiary 1150–1200 cm−1 medium
phenols any 1200 cm−1
ethers aliphatic 1120 cm−1
aromatic 1220–1260 cm−1
carboxylic acids any 1250–1300 cm−1
esters any 1100–1300 cm−1 two bands (distinct from ketones, which do not possess a C─O bond)
C─N aliphatic amines any 1020–1220 cm−1 often overlapped
C═N any 1615–1700 cm−1 similar conjugation effects to C═O
C≡N (nitriles) unconjugated 2250 cm−1 medium
conjugated 2230 cm−1 medium
R─N─C (isocyanides) any 2165–2110 cm−1
R─N═C═S any 2140–1990 cm−1
C─Halide|X fluoroalkanes ordinary 1000–1100 cm−1
trifluromethyl 1100–1200 cm−1 two strong, broad bands
chloroalkanes any 540–760 cm−1 weak to medium
bromoalkanes any 500–600 cm−1 medium to strong
iodoalkanes any 500 cm−1 medium to strong
N─O nitro compounds aliphatic 1540 cm−1 stronger
1380 cm−1 weaker
aromatic 1520, 1350 cm−1 lower if conjugated
Last modified on 10 June 2010, at 02:57