# 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 |
| C─H | alkyl | methyl | 1380 cm$^{−1}$ | weak |
| C─H | alkyl | methyl | 2870 cm$^{−1}$ | medium to strong |
| C─H | alkyl | methyl | 2960 cm$^{−1}$ | medium to strong |
| C─H | alkyl | methylene | 1470 cm$^{−1}$ | strong |
| C─H | alkyl | methylene | 2850 cm$^{−1}$ | medium to strong |
| C─H | alkyl | methylene | 2925 cm$^{−1}$ | medium to strong |
| C─H | alkyl | methine | 2890 cm$^{−1}$ | weak |
| C─H | vinyl | C═CH$_2$ | 900 cm$^{−1}$ | strong |
| C─H | vinyl | C═CH$_2$ | 2975 cm$^{−1}$ | medium |
| C─H | vinyl | C═CH$_2$ | 3080 cm$^{−1}$ | medium |
| C─H | vinyl | C═CH | 3020 cm$^{−1}$ | medium |
| C─H | vinyl | monosubstituted alkenes | 900 cm$^{−1}$ | strong |
| C─H | vinyl | monosubstituted alkenes | 990 cm$^{−1}$ | strong |
| C─H | vinyl | cis-disubstituted alkenes | 670–700 cm$^{−1}$ | strong |
| C─H | vinyl | trans-disubstituted alkenes | 965 cm$^{−1}$ | strong |
| C─H | vinyl | trisubstituted alkenes | 800–840 cm$^{−1}$ | strong to medium |
| C─H | aromatic | benzene/sub. benzene | 3070 cm$^{−1}$ | weak |
| C─H | aromatic | monosubstituted benzene | 700–750 cm$^{−1}$ | strong |
| C─H | aromatic | monosubstituted benzene | 690–710 cm$^{−1}$ | strong |
| C─H | aromatic | ortho-disub. benzene | 750 cm$^{−1}$ | strong |
| C─H | aromatic | meta-disub. benzene | 750–800 cm$^{−1}$ | strong |
| C─H | aromatic | meta-disub. benzene | 860–900 cm$^{−1}$ | strong |
| C─H | aromatic | para-disub. benzene | 800–860 cm$^{−1}$ | strong |
| C─H | alkynes | any | 3300 cm$^{−1}$ | medium |
| C─H | aldehydes | any | 2720 cm$^{−1}$ | medium |
| C─H | aldehydes | any | 2820 cm$^{−1}$ | medium |
| C─C | acyclic C─C | monosub. alkenes | 1645 cm$^{−1}$ | medium |
| C─C | acyclic C─C | 1,1-disub. alkenes | 1655 cm$^{−1}$ | medium |
| C─C | acyclic C─C | cis-1,2-disub. alkenes | 1660 cm$^{−1}$ | medium |
| C─C | acyclic C─C | trans-1,2-disub. alkenes | 1675 cm$^{−1}$ | medium |
| C─C | acyclic C─C | trisub., tetrasub. alkenes | 1670 cm$^{−1}$ | weak |
| C─C | conjugated system|conjugated C─C | dienes | 1600 cm$^{−1}$ | strong |
| C─C | conjugated system|conjugated C─C | dienes | 1650 cm$^{−1}$ | strong |
| C─C | with benzene ring | dienes | 1625 cm$^{−1}$ | strong |
| C─C | with C═O | dienes | 1600 cm$^{−1}$ | strong |
| C─C | C═C (both sp$^2$) | any | 1640–1680 cm$^{−1}$ | medium |
| C─C | aromatic C═C | any | 1450 cm$^{−1}$ | weak to strong (usually 3 or 4) |
| C─C | aromatic C═C | any | 1500 cm$^{−1}$ | weak to strong (usually 3 or 4) |
| C─C | aromatic C═C | any | 1580 cm$^{−1}$ | weak to strong (usually 3 or 4) |
| C─C | aromatic C═C | any | 1600 cm$^{−1}$ | weak to strong (usually 3 or 4) |
| C─C | C≡C | terminal alkynes | 2100–2140 cm$^{−1}$ | weak |
| C─C | C≡C | disubst. alkynes | 2190–2260 cm$^{−1}$ | very weak (often indisinguishable) |
| C═O | aldehyde/ketone | saturated aliph./cyclic 6-membered | 1720 cm$^{−1}$ | |
| C═O | aldehyde/ketone | α,β-unsaturated | 1685 cm$^{−1}$ | |
| C═O | aldehyde/ketone | aromatic ketones | 1685 cm$^{−1}$ | |
| C═O | aldehyde/ketone | cyclic 5-membered | 1750 cm$^{−1}$ | |
| C═O | aldehyde/ketone | cyclic 4-membered | 1775 cm$^{−1}$ | |
| C═O | aldehyde/ketone | aldehydes | 1725 cm$^{−1}$ | influence of conjugation (as with ketones) |
| C═O | carboxylic acids/derivates | saturated carboxylic acids | 1710 cm$^{−1}$ | |
| C═O | carboxylic acids/derivates | unsat./aromatic carb. acids | 1680–1690 cm$^{−1}$ | |
| C═O | carboxylic acids/derivates | esters and lactones | 1735 cm$^{−1}$ | influenced by conjugation and ring size (as with ketones) |
| C═O | carboxylic acids/derivates | anhydrides | 1760 cm$^{−1}$ | |
| C═O | carboxylic acids/derivates | anhydrides | 1820 cm$^{−1}$ | |
| C═O | carboxylic acids/derivates | acyl halides | 1800 cm$^{−1}$ | |
| C═O | carboxylic acids/derivates | amides | 1650 cm$^{−1}$ | associated amides |
| C═O | carboxylic acids/derivates | carboxylates (salts) | 1550–1610 cm$^{−1}$ | |
| C═O | carboxylic acids/derivates | amino acid zwitterions | 1550–1610 cm$^{−1}$ | |
| O─H | alcohols, phenols | low concentration | 3610–3670 cm$^{−1}$ | |
| O─H | alcohols, phenols | high concentration | 3200–3400 cm$^{−1}$ | broad |
| O─H | carboxylic acids | low concentration | 3500–3560 cm$^{−1}$ | |
| O─H | carboxylic acids | high concentration | 3000 cm$^{−1}$ | broad |
| N─H | primary amines | any | 3400–3500 cm$^{−1}$ | strong |
| N─H | primary amines | any | 1560–1640 cm$^{−1}$ | strong |
| N─H | secondary amines | any | >3000 cm$^{−1}$ | weak to medium |
| N─H | ammonium ions | any | 2400–3200 cm$^{−1}$ | multiple broad peaks |
| C─O | alcohols | primary | 1040–1060 cm$^{−1}$ | strong, broad |
| C─O | alcohols | secondary | ~1100 cm$^{−1}$ | strong |
| C─O | alcohols | tertiary | 1150–1200 cm$^{−1}$ | medium |
| C─O | phenols | any | 1200 cm$^{−1}$ | |
| C─O | ethers | aliphatic | 1120 cm$^{−1}$ | |
| C─O | ethers | aromatic | 1220–1260 cm$^{−1}$ | |
| C─O | carboxylic acids | any | 1250–1300 cm$^{−1}$ | |
| C─O | 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 | C═N | any | 1615–1700 cm$^{−1}$ | similar conjugation effects to C═O |
| C─N | C≡N (nitriles) | unconjugated | 2250 cm$^{−1}$ | medium |
| C─N | C≡N (nitriles) | conjugated | 2230 cm$^{−1}$ | medium |
| C─N | R─N─C (isocyanides) | any | 2165–2110 cm$^{−1}$ | |
| C─N | R─N═C═S | any | 2140–1990 cm$^{−1}$ | |
| C─Halide|X | fluoroalkanes | ordinary | 1000–1100 cm$^{−1}$ | |
| C─Halide|X | fluoroalkanes | trifluromethyl | 1100–1200 cm$^{−1}$ | two strong, broad bands |
| C─Halide|X | chloroalkanes | any | 540–760 cm$^{−1}$ | weak to medium |
| C─Halide|X | bromoalkanes | any | 500–600 cm$^{−1}$ | medium to strong |
| C─Halide|X | iodoalkanes | any | 500 cm$^{−1}$ | medium to strong |
| N─O | nitro compounds | aliphatic | 1540 cm$^{−1}$ | stronger |
| N─O | nitro compounds | aliphatic | 1380 cm$^{−1}$ | weaker |
| N─O | nitro compounds | aromatic | 1520, 1350 cm$^{−1}$ | lower if conjugated |