Structure & Reactivity
Infrared Spectroscopy
IR12. Appendix
Table of IR Absorptions Common in Organic Compounds
Note: strong, medium, weak refers to the length of the peak (in the y axis direction).
Note: spectra taken by ATR method (used at CSB/SJU) have weaker peaks between 4000-2500 cm-1 compared to reference spectra taken by transmittance methods (typical on SDBS and other sites).
Approximate Frequency (cm-1) | Description | Bond Vibration | Notes |
3500 - 3200 | broad, round | O-H | much broader, lower frequency (3200-2500) if next to C=O |
3400-3300 | weak, triangular | N-H | stronger if next to C=O |
3300 | medium-strong | =C-H (sp C-H) | |
3100-3000 | weak-medium | =C-H (sp2 C-H) | can get bigger if lots of bonds present |
3000-2900 | weak-medium | -C-H (sp3 C-H) | can get bigger if lots of bonds present |
2800 and 2700 | medium | C-H in O=C-H | two peaks; "alligator jaws" |
2250 | medium | C=N | |
2250-2100 | weak-medium | C=C | stronger if near electronegative atoms |
1800-1600 | strong | C=O | lower frequency (1650-1550) if attached to O or N middle frequency if attached to C, H higher frequency (1800) if attached to Cl |
1650-1450 | weak-medium | C=C | lower frequency (1600-1450) if conjugated (i.e. C=C-C=C) often several if benzene present |
1600-1450 | medium | H-N-H bend | often broad |
1530 and 1360 | strong | N=O in -NO2 | two peaks |
1450 | weak-medium | H-C-H bend | |
1300 and 1200 | strong | S=O in sulfonate | two peaks |
1300-1200 | strong | P=O in phosphate | often double peak |
1300 - 1000 | medium-strong | C-O | higher frequency (1200-1300) if conjugated (i.e. O=C-O or C=C-O) |
1300-1100 | strong | C-F | C-F is much less common than C-O |
1250-1000 | medium | C-N | |
1000-650 | strong | C=C-H bend | often several if benzene present |
800 | strong | N-O | |
750-600 | strong | C-Cl | C-Br and C-I are below 650 |
This is a good starter table. Other tables may be more complete:
Central Connecticut State University IR Table includes more exotic bonds such as N=O, S=O, P=O, C-Cl, C-Br etc.
Michigan State IR Page includes IR tables.
This site was written by Chris P. Schaller, Ph.D., College of Saint Benedict / Saint John's University (retired) with other authors as noted on individual pages. It is freely available for educational use.
Structure & Reactivity in Organic, Biological and Inorganic Chemistry by Chris Schaller is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License.
Send corrections to cschaller@csbsju.edu
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