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3.12: Appendix

  • Page ID
  • 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