Gas Chromatography - Tandem Techniques - The Characteristics of Infrared Absorption > The Measurement of IR Absorption > Page 27

The presence of certain bands at specific wave numbers helps identify the major groups present in the molecule but gives very little evidence on the size of the molecule or the manner in which the actual groups are joined.

It is seen that the vapor and liquid spectra are indeed very similar and can be confidently used to confirm sample identity. It should be noted that the dispersed peak at about 3400 wave numbers, shown in the liquid sample spectrum (which is not present in the vapor spectrum), is probably due to the effect of intra-hydrogen bonding between the OH groups of the n-hexanol and water possibly present in the sample or solvent. Spectra identification and interpretation are best carried out using digitized spectra in conjunction with appropriate comparison or identification software. However, if using analog data, correlation charts can be constructed to help assign specific absorption bands to certain chemical bonds or groups present in an unknown molecule. An example of such a correlation chart, after Stuart (8), is shown in figure 17.

The presence of certain bands at specific wave numbers helps identify the major groups present in the molecule but gives very little evidence on the size of the molecule or the manner in which the actual groups are joined.

 

 

Figure 17 An IR Correlation Chart for Interpreting IR Spectra