Modern Polymer Spect..

164 3 li'hratioiziil Spectra as a Probe oj'StrzictLira1 Order
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400 200 0
Frequency (cm-' )
Figure 3-36. Rainan spectra (0-400 cm-' ) of (a) hexatriacontane, n-C36H74; (b) stearic acid,
n-Cl7H35COOH and (c) strearyl alcohol, n-ClgH17OH. Notice that since fatty scids and alcohols
form head-to-head hydrogen-bonded diniers LAM modes extend throughout the whole dirneric
system. Thus, the LAM progression shifts toward much lower frequencies than those expected for
one isolated chain, approaching the values of hexatriacontane. The lowest frequency strong LAM1
mode has its node at the center of the molecule, inside the hydrogen-bonded diineric structure (see
text).
powerful and essential diagnostic tool on the conformatioilally ordered/disordered
structure of complex organic, biological and industrially relevant polyinethylene
materials which contain polymethylene chains.
The reason of such peculiar aid specific spectroscopic manifestations is that
complex Fermi resonance phenomena occur in molecules containing polymethylene
chains. We are concerned in this chapter on the Ferini resonances associated with
the vibrations of polymethylene systems in the trans or gauche states, considered
either as isolated entities and/or when they are organized in ordered and/or disordered
supermolecular structures. Let us remember that Ferini resoiiaiice derives