Question

Breiefly describe the theory behind an absorption band in an IR spectrum?

Answer 1

IR spectra look quite complex because the bond vibration create absorption band.the intensity of the absorption band depends on the change in the dipole moment of the bond the number of the specific bond presents the bond dipole results from two things the bond length and the charge difference between the two atoms.w hen the molecule absorb a photon,it stretches bond length changes if we have two different atoms will there will be an electronegativity photon will be absorbed.if there is no electronegativity difference such as in an o2 and n2.t hen q photon will not be absorbed and the molecule will not be excited to a higher vibrational state if you compare the ir spectra the methane to that of octane,t he octane molecule will have a much more intense C-H peak because it has many more C-H bonds than methane.

Thus,the horizontal position of the absorption that corresponds to a different energy,the strength of the bond and the masses of the bonded atoms are crucial in determining stretching energy.f or example triple bond stronger than double bonds which are in turn stronger than single bonds