In the pre-lecture we saw that FT-IR spectroscopy probes molecular vibrations, treating the molecule like a series of masses on springs. In this model, the spring constant k is related to the strength of the bond. The equation describing the vibrational frequency of a mass-spring system is:

v= 1/ 2π √K/μ

Where v is the vibrational frequency, k is the spring constant and u is the reduced mass. From this justify the following trend in IR absorptions for alkyl halides.

Bond Absorption Position(cm^-1)
C-F 1000-1400
C-Cl 600-800
C-Br 500-600
C-l 500