Structure & Reactivity
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"|
|2250-2100||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
often several if benzene present
|1600-1450||medium||H-N-H bend||often broad|
|1530 and 1360||strong||N=O in -NO2||two peaks|
|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|
|1000-650||strong||C=C-H bend||often several if benzene present|
|800-600||strong||C-Cl||C-Br and C-I are below 600|
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.
UCLA IR Table
Wikipedia IR Table
This site is written and maintained by Chris P. Schaller, Ph.D., College of Saint Benedict / Saint John's University (with contributions from other authors as noted). 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 firstname.lastname@example.org
Back to Infrared Spectroscopy
Back to Structure Determination
Back to Structure & Reactivity Appendix
Back to Structure & Reactivity