IR Spectroscopy

IR Spectroscopy

1. General Info

   • Molecules only absorb the exact amount of energy needed to excite them from a ground state to a higher level
   • In IR, absorptions are used for bond stretching and bending
     • Each functional group will have its own absorptions
     • You can use IR spectra to determine if a functional group is present in a molecule
   • Absorbed frequency is expressed in wave#'s or reciprocal centimeres
     • they range from 4000-400 cm-1

2. Interpreting IR Spectra

   • has certain basic regions; use these to perform a preliminary analysis of which types of groups may be present
     • If a band is present it means that functional groups is likely in the molecule
     • If a band is not present, that functional group is not in the molecule
   • Basic regions
     • 3300-3640=>O-H, N-H stretch
     • 3000-3300=> CtripleC-H, C=C-H stretch
       • 2800-3000 sp3-> C-C-H stretch
     • 2000-2300 CTripleC, CtripleN stretch
     • 1600-1850 C=C, C=O stretch
     • 400-1500 Finger print region
       • Too many bands to use for exact matches