Spectroscopy Reference
Quick-reference tables for IR, NMR, and mass spectrometry — the data organic chemistry students look up most.
Infrared (IR) absorption correlation table. Wavenumber ranges in cm⁻¹.
| Functional Group | Range (cm⁻¹) | Intensity | Notes |
|---|---|---|---|
| O-H (alcohol, free) | 3580–3650 | strong, sharp | Free (non-hydrogen-bonded) hydroxyl stretch |
| O-H (alcohol, H-bonded) | 3200–3550 | strong, broad | Hydrogen-bonded hydroxyl stretch; breadth depends on extent of bonding |
| O-H (carboxylic acid) | 2500–3300 | strong, very broad | Overlaps with C-H stretches; characteristic broad absorption |
| N-H (amine, amide) | 3300–3500 | medium | Primary amines show two peaks; secondary amines show one |
| C-H (alkane, sp³) | 2850–2960 | strong | Symmetric and asymmetric stretches of CH₃ and CH₂ groups |
| C-H (alkene, sp²) | 3020–3100 | medium | =C-H stretch; appears just above 3000 cm⁻¹ |
| C-H (alkyne, sp) | 3300–3320 | strong, sharp | Terminal ≡C-H stretch; distinctive sharp peak |
| C-H (aldehyde) | 2700–2850 | medium, two peaks | Fermi resonance doublet characteristic of aldehydes |
| C-H (aromatic) | 3000–3100 | medium | Aromatic C-H stretch; just above 3000 cm⁻¹ |
| C≡N (nitrile) | 2210–2260 | medium-strong | Triple bond stretch; conjugation lowers frequency |
| C≡C (alkyne) | 2100–2260 | variable | Absent in symmetrical internal alkynes; weak in many cases |
| C=O (ketone) | 1705–1725 | strong | Conjugation lowers frequency; ring strain raises it |
| C=O (aldehyde) | 1720–1740 | strong | Slightly higher than ketones |
| C=O (carboxylic acid) | 1700–1725 | strong | Dimeric form in solution |
| C=O (ester) | 1735–1750 | strong | Higher than ketones; conjugation lowers frequency |
| C=O (amide) | 1630–1690 | strong | Amide I band; resonance lowers C=O frequency |
| C=O (anhydride) | 1800–1830 | strong, two bands | Two C=O stretches; lower band near 1740-1770 cm⁻¹ |
| C=O (acid chloride) | 1770–1815 | strong | Higher than esters due to inductive effect of Cl |
| C=C (alkene) | 1620–1680 | variable | Weak or absent in symmetrical alkenes |
| C=C (aromatic) | 1450–1600 | variable | Ring stretching; two or three bands in this region |
| N-H (amide II bend) | 1510–1570 | strong | N-H bend coupled with C-N stretch |
| C-O (alcohol, ether) | 1000–1260 | strong | Position varies: primary ~1050, secondary ~1100, tertiary ~1150 cm⁻¹ |
| C-N (amine) | 1020–1250 | medium | Difficult to assign definitively; often overlaps with C-O |
| N-O (nitro) | 1500–1570 | strong, two bands | Asymmetric stretch ~1550; symmetric stretch ~1350 cm⁻¹ |
| S=O (sulfoxide) | 1030–1070 | strong | Single S=O stretch |
| S=O (sulfone) | 1120–1160 | strong, two bands | Asymmetric and symmetric S=O stretches |
| C-F | 1000–1400 | strong | C-F stretch; very strong absorption |
| C-Cl | 600–800 | strong | C-Cl stretch |
| C-Br | 500–680 | strong | C-Br stretch |
Absorption Range Visualization (4000–400 cm⁻¹)
O-H (alcohol, free)
O-H (alcohol, H-bonded)
O-H (carboxylic acid)
N-H (amine, amide)
C-H (alkane, sp³)
C-H (alkene, sp²)
C-H (alkyne, sp)
C-H (aldehyde)
C-H (aromatic)
C≡N (nitrile)
C≡C (alkyne)
C=O (ketone)
C=O (aldehyde)
C=O (carboxylic acid)
C=O (ester)
C=O (amide)
C=O (anhydride)
C=O (acid chloride)
C=C (alkene)
C=C (aromatic)
N-H (amide II bend)
C-O (alcohol, ether)
C-N (amine)
N-O (nitro)
S=O (sulfoxide)
S=O (sulfone)
C-F
C-Cl
C-Br
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