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Chapter III CHN Analysis, FT IR …..
given type of group or groups. Although group frequencies occur within narrow
limits, interference or perturbation may cause a shift of the characteristic
bands due to (a) the electro negativity of neighboring groups or atoms, (b) the
spatial geometry of the molecule or (c) the mechanical mixing of vibrational
modes.
Functional groups sometimes have more than one characteristic
absorption band associated with them. On the other hand, two or more
functional groups may absorb in the same region and hence, in general, can
only be distinguished from each other by means of other characteristic infrared
bands, which occur in non-over lapping regions.
Absorption bands may be considered as having two origins, these
being the fundamental vibrations of (a) functional groups, e.g. C=O, C=C,
C≡N, CH2, CH3 and (b) skeletal groups, i.e. the molecular backbone or
skeleton of the molecule e.g., C-C-C-C. Absorption bands may also arise from
stretching vibrations, i.e., vibrations involving bond-length changes or
deformation vibration, i.e., vibrations involving bond-angle changes of the
group. Each of these, in some cases, may be considered as arising from
symmetric or asymmetric vibrations. For a given functional group, the vibration
bands due to stretching occur at higher frequencies than those due to
deformation. This is because more energy requires to stretch the group than to
deform it due to the bonding force directly opposing the change.
3.7 FTIR Studies of Pure and Amino Acids Doped KDP Crystals
Many researchers have studied the FT-IR spectra of pure and doped KDP
crystals. FTIR spectra of the pure KDP and doped with CH3COOK (5 mol%)
and K3C6H5O7 (5 mol%) studied by Dhanaraj et al [14] . They observed broad
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