This approach is based on experimental observations and comes from a careful comparison of many spectra.
| Substance class | Group | Absorption range, cm –1 | Intensity | Comments (1) |
| Alkanes and alkyl fragments | C – H shaft. | 3000-2840 | variable | Outside the usual range, C – H stretching vibrations appear for methyl ethers (2850-2815), other ethers (2880-2830), oxirane and aziridine (3050-3000), amines (2820-2780), cyclopropane and cyclohexane (3100 —3050, 3035—2995). |
| CH 3 def. | 1470-1430 1395-1365 1250-800 | mean mean variable | The absorption bands in the 1250-800 region are of no practical importance. | |
| CH 2 def. | 1475-1450 770-720 | average average | ||
| C – D shaft. | 2200-2080 | |||
| Alkenes | = CH 2 shaft. | 3095-3075 | average | Often several stripes. |
| = CH shaft. | 3040-3010 | average | Often several stripes. | |
| = CH def. | 1420-1290 ( flat ) 1005-675 ( out-of-plane ) | – | Out-of-plane oscillations are of no practical importance. | |
| C = C shaft. | 1690-1635 | variable | For trans- disubstituted alkenes – 1690-1665 of low intensity, for cis -isomers – 1665-1635. For tri- and tetrasubstituted alkenes, it is in the range of 1690-1650 and is often absent. The frequency decreases when conjugated with another C = C-bond (1650, 1600), triple bond (1600), nitrile group (1620), carbonyl group (1630), benzene ring (1630). | |
| Alkyne | ≡C – H shaft. | 3340-3250 | strong | The same region contains the bands of stretching vibrations O – H and N – H. |
| C≡C shaft. | 2260-2100 | weak | For terminal alkynes, vibrations of the triple bond appear at the low-frequency end of this range. In symmetrical structures, the band is often absent. | |
| ≡C – H def. | 700-600 | strong | At 1370-1220, a wide and weak overtone of this oscillation is manifested. | |
| Alicyclic compounds | C – H shaft. | 3090-2860 | strong | |
| H – C – H def. | 1470-1430 | weak | ||
| C = C def. | 1780-1610 | variable | ||
| Aromatic hydrocarbons | C – H shaft. | 3080-3030 | A set of stripes is often observed. Stretching vibrations of C – H bonds in alkenes fall into the same region. | |
| C – C | 1625-1575, 1525-1475 | average | Often there are two stripes. | |
| combinational | 2000-1650 | very weak | By the nature of absorption in this area, the type of substitution of the aromatic ring is established. | |
| C – H def. | variable strong | Out-of-plane absorption bands are used to determine the type of substitution in aromatic compounds. | ||
| Organofluorine compounds | C – F shaft. | 1400-1000 | strong | More than one band is often observed due to the presence of rotational isomers . |
| S – F shaft. | 815-755 | strong | ||
| P – F shaft. | 1110-760 | |||
| Si – F shaft. | 980-820 | |||
| B – F shaft. | 1500-800 | |||
| Organochlorine compounds | C – Cl shaft. | 1100-1020, 830- <600 | strong | |
| C – Cl def. | 400-280 | average | ||
| P – Cl shaft. | <600 | |||
| Si – Cl shaft. | <625 | |||
| B – Cl shaft. | 1100-650 | |||
| Organobromine compounds | C – Br shaft. | 1080-1000, 700-500 | strong | |
| C – Br def. | 350-250 | average | ||
| Organoiodine compounds | C – I shaft. | 650-450 | strong | Two or more stripes. |
| C – I def. | 300-50 | average | ||
| Alcohols and phenols | O – H shaft. | 3650-3200 | variable | The absorption bands of hydroxyl groups bound by hydrogen bonds have an increased width and are shifted to a lower frequency region (3550-3450) compared to free (3650-3590). |
| O – H def. flat | 1450-1200 | average | There is no practical relevance. | |
| C – O shaft. | 1260-970 | strong | Primary alcohols: 1075-1000, secondary alcohols: 1125-1000, tertiary alcohols: 1210-1100, phenols: 1275-1150. | |
| O – H def. out-of-plane. | <700 | average | There is no practical relevance. | |
| Ethers and acetals | C – O – C shaft. asim. | 1310-1000 | strong | Sometimes the band is split into 3, 4 or 5 components. |
| C – O – C shaft. Sim. | 1055-870 | strong | Sometimes several stripes. | |
| Peroxides | O – O – H shaft. | 3450-3200 | variable | |
| C – O – O shaft. | 1200-1000 | strong | ||
| O – O shaft. | 1000-800 | medium or weak | The assignment is unreliable. | |
| Amines | NH 2 shaft. | 3500-3300 | variable | Primary amines give two narrow bands in this region. When a hydrogen bond is formed, the vibration frequency decreases, and the bands broaden. Sometimes free and hydrogen-bonded forms are observed simultaneously. |
| NH shaft. | 3450-3300 | variable | Secondary amines give only one lane. When a hydrogen bond is formed, the vibration frequency decreases, and the bands broaden. Sometimes free and hydrogen-bonded forms are observed simultaneously. | |
| NH 3 + , NH 2 + , NH + shaft. | 3000-2000 | average | Wide, highly structured strip. | |
| NH 2 def. | 1650-1590, 850-700 | medium or weak | ||
| NH def. | 1650-1550, 850-700 | weak | ||
| NH 3 + , NH 2 + , NH + def. | 1600-1460 | average | More than one band is often observed. The band is weak for aliphatic amines. | |
| C – N shaft. | 1400-1000 | average | There is no practical value. | |
| Nitro compounds and nitroso compounds | NO 2 shaft. asim. | 1660-1490 | very strong | |
| NO 2 shaft. Sim. | 1390-1260 | strong | ||
| N = O shaft. | 1680-1450 (monomers), 1420-1250 (dimers) | very strong | ||
| C – N shaft. | ≈850 (alip. Nitroso compounds), ≈1100 (arom. Nitroso compounds) | |||
| Imines and oximes | C = N shaft. | 1690-1520 | usually strong | |
| O – H shaft. | 3600-2700 | strong | ||
| O – H def. | 1475-1315 | There is no practical value. | ||
| Azo compounds | N = N shaft. | 1500-1400 | very weak | Not present in high-symmetry connections. |
| Nitriles and isonitriles | C≡N shaft. | 2260-2240 | medium or strong | |
| Diazo compounds | N + ≡N shaft. | 2310-2130 | average | The frequency depends on the anion. |
| C = N + = N shaft. | 2050-2010 | very strong | ||
| Cyanates and isocyanates | OC≡N shaft. | 2260-2130 | medium or strong | |
| C – O shaft. | 1200-1080 | strong | ||
| N = C = O shaft. asim. | 2280-2230 | strong | ||
| N = C = O shaft. Sim. | 1450-1380 | weak | ||
| Thiocyanates and thioisocyanates | SC≡N shaft. | 2170-2130 | average | |
| C – S shaft. | 750-550 | Often two stripes. | ||
| N = C = S shaft. asim. | 2200-2050 | very strong | Usually two bands, Fermi resonance | |
| N = C = S shaft. Sim. | 950-650 | |||
| Thiols and sulfides | S – H shaft. | 2600-2540 | weak | |
| S – H def. | 915-800 | weak | There is no practical value. | |
| C – S shaft. | 710-570 | weak | There is no practical value. | |
| S – S shaft. | ≈500 | weak | There is no practical value. | |
| Sulfoxides and sulfones | S = O shaft. | 1225-980 | strong | Sometimes several stripes. |
| SO 2 shaft. | 1420-1000 | very strong | ||
| S – O shaft. | 870-690 | variable | ||
| Aldehydes | C – H comb. | 2900-2800, 2780-2680 | weak | Fermi resonance. |
| C = O shaft. | 1765-1645 | strong | Aliphatic aldehydes give a band at 1740-1720 cm –1 . In the presence of conjugation, the vibration frequency decreases: aromatic aldehydes (1710-1685), α, β-unsaturated aldehydes (1695-1660). For α-halogenaldehydes, this frequency is higher (1765-1730). | |
| Ketones | C = O shaft. | 1775-1650 | strong | Aliphatic ketones give a band at 1715 cm –1 . Conjugation shifts the band towards lower frequencies (aromatic ketones: 1690, α, β-unsaturated ketones: 1675). α-Diketones absorb at 1720 cm –1 , β-diketones – at 1720 and 1650 cm –1 (keto form and enol form, respectively). |
| Carboxylic acids | COO – H shaft. | 3550-2500 | variable | In strongly dilute solutions, a narrow band appears at 3550–3500 cm –1 . With the formation of hydrogen bonds, the frequency decreases, and the band broadens. |
| C = O shaft. | 1800-1650 | strong | Free groups absorb at 1800-1740 cm –1 , in the presence of hydrogen bonds, the frequency decreases to 1740-1650 cm –1 . α, β-Unsaturated carboxylic acids: 1715-1690 cm –1 , aromatic carboxylic acids: 1700-1680 cm –1 . | |
| Esters | C = O shaft. | 1790-1650 | strong | Aliphatic esters absorb at 1750-1735 cm –1 , when conjugated, this frequency decreases (α, β-unsaturated esters: 1730-1710, aromatic esters: 1730-1715). α-Halogenated derivatives absorb at 1790-1740 cm –1 . |
| C – O shaft. | 1330-1050 | strong | Two bands: an antisymmetric band with a higher frequency and a symmetric band with a lower frequency. | |
| Amides | N – H shaft. | 3500-3100 | average | Primary amides have two bands. |
| C = O shaft. (amide I) | 1740-1630 | strong | ||
| N – H def. and N – C = O shaft. (amide II) | 1630-1510 | strong | The band is absent in the lactams. | |
| Carboxylic acid anhydrides | C = O shaft. | 1870-1770, 1800-1720 | strong | Symmetrical and asymmetric bands, respectively. |
| C – O – C shaft. | 1300-900 | strong | Several stripes. | |
| Halides of carboxylic acids | C = O shaft. | 1820-1750 shaft. | strong | Typical for acid chlorides. For acid bromides or acid iodides at a lower frequency. |
| 1900-1870 shaft. | strong | Fluoroanhydrides. | ||
| C – Hal shaft. | 1200-500 | Fluoroanhydrides – 1200-800, acid chlorides – 750-500, acid bromides – 700-500, acid iodides – 600-500. | ||
| Organosilicon compounds | Si – H shaft. | 2250-2090 | average | |
| Si – H def. | 1010-700 | strong | Usually two wide stripes. | |
| Si – O shaft. | 1100-1000, 900- <600 | |||
| Si – C shaft. | 850-650 | |||
| Si – N shaft. | 1250-830 | |||
| Si – F shaft. | 980-820 | |||
| Si – Cl shaft. | <625 | |||
| Organophosphorus compounds | P – H shaft. | 2440-2275 | weak or medium | |
| PO – H shaft. | 2700-2650 | weak | Very wide band. | |
| POH comb. | 2300-2250 | weak | Very wide band. | |
| P – O shaft. | 1260-855 | |||
| P = O shaft. | 1300-960 | strong | ||
| P = N shaft. | 1500-1170 | |||
| P – C shaft. | 800-700 | different | There is no practical application. | |
| P – H def. | 1090-910 | strong | ||
| Organoboron compounds | B – H shaft. | 2640-2200 | strong | |
| B – O shaft. | 1380-1310 | very strong | ||
| B – OH shaft. | 3300-3200 | Very wide band. | ||
| B – N shaft. | 1550-1330 | very strong | ||
| B – C shaft. | 1240-620 | strong | For very asymmetric molecules, there are two bands. | |
| B – F shaft. | 1500-800 | |||
| B – Cl shaft. | 1100-650 |