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  
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.

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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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