The X—H Stretching Region 4000-2500 cm

Ail of the fundamental vibrations in the region between 4000 and 2500 cm may be attributed to X—stretching. For example, O—H. stretching produces a broad band which occurs in the range. 

3700-3600 cm-i. In comparison, N—H stretching is usually observed between 3400 and 3300 cm This absorption is generally much sharper than O—stretching and may therefore be differentiated. Compounds containing the NH2 group usually show a doublet structure, while secondary amines show only one sharp band. 

The C—stretching bands from aliphatic compounds occur in the range 3000-2850 cm- They are moderately broad and show medium intensity. It is also possible to resolve the asymmetrical and symmetrical C—H stretching absorptions of a CH3 group, which usually occur at about 2965 and 2880 cm i, respectively, while the corresponding absorptions for a CH2 group occur at 2930 and 2860 cm-i. 

Deuterated compounds would be expected to show C—D stretching at a factor of 0.73 less than that of the C—stretching, due to the change in atomic mass (remember SAQ 1.4b), i.e. at 2130 cm k 

The S—stretching frequency is very weak, and may even be too weak to observe. 

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The X-H stretch region (4000-2500 cm 1), where strong contributions from OH, NH, CH and SH stretch vibrations are observed,... 

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