The monochromator allows only one frequency of light to enter at any given time.It scans the range of IR frequencies from 4000-600cm The vertical axis is percentage transmittance and the horizontal axis contains the wavenumber. Typically the higher wavenumber are to the left of an IR spectrum. IR Spectroscopy of Hydrocarbons Carbon-Carbon Bond Stretching Since stronger bonds are generally stiffer,they absorb at higher frequencies than weaker bonds. Single C-C bonds absorb around cm Double C-C bonds absorb around 1660cm Triple CC bonds absorb around 2200cm The absorptions of C=C bonds can provide more information about the double bond. Conjugation(and more)cause there to be less double bond character in the C=C bond,which results in absorption at a lower wavenumber. Ch12 IR and MS Page8 The monochromator allows only one frequency of light to enter at any given time. It scans the range of IR frequencies from 4000 - 600cm-1. The vertical axis is percentage transmittance and the horizontal axis contains the wavenumber. Typically the higher wavenumber are to the left of an IR spectrum. IR Spectroscopy of Hydrocarbons Carbon-Carbon Bond Stretching Since stronger bonds are generally stiffer, they absorb at higher frequencies than weaker bonds. Single C-C bonds absorb around 1200cm-1 Double C=C bonds absorb around 1660cm-1 Triple CC bonds absorb around 2200cm-1. The absorptions of C=C bonds can provide more information about the double bond. Conjugation (and more so, aromaticity) cause there to be less double bond character in the C=C bond, which results in absorption at a lower wavenumber. Ch12 IR and MS Page8