The Infrared Spectra of Lignin and Related Compounds. I. Characteristic Carbonyl and Hydroxyl Frequencies of Some Flavanones, Flavones, Chalcones and Acetophenones¹

Fourier Transform Infrared Spectroscopy for Natural Fibres

“…The major compositions of lignocellulosic fibres are cellulose, hemicellulose and lignin (see Figure 10), while the minor constituents include minerals, pectin, waxes and water-soluble components. The application of infrared spectroscopy in lignocellulosic fibres has a long history: The infrared spectroscopy was used to investigate the hydroxyl groups of cellulose in the 1930's [53] and significant efforts were made in the 1950's to assign the different absorption maxima in the IR spectrum of cellulose [54][55][56][57][58][59]; The absorption maxima in the IR spectra of lignin were investigated from 1940's [60-61] through 1950's [62][63][64]; The characteristic absorption maxima of hemicellulose were studied during the 50's [65][66]. Fig.…”

Infrared Spectroscopic Investigations of Effect of Strong Resonance Stabilized Intramolecular Hydrogen Bonding in 1-(1-Hydroxy-2-naphthyl)-3-(phenyl or Substituted phenyl)-prop-2-en-1-ones and on their Complexation with Some Transition Metals

“…As discussed earlier, it must be restated that intramolecular hydrogen bonding between carbonyl and hydroxyl groups shows lowering in carbonyl frequency 53,61 . The values obtained by the earlier researchers 26 for some of the bands observed in the ligands BenchaH and p-AnichaH and their complexes are also given in Tables 1 and 2.…”

“…Thus, from 2'-hydroxychalcone (the parent hydroxylchalcone) to the corresponding isomeric naphthalene analogues i.e. the parent isomeric hydroxynaphthyl chalcones, the replacement of the hydroxy phenyl ring by the hydroxyl naphthyl ring further shifts the carbonyl band from 1639 to 1628-1622 cm -1 and this further lowering in frequency may attributed to the extended conjugation 52,53 . Chem Sci Trans., 2015, 4(2), 463-477…”

“…Hence, assignment of all the bands without ambiguity is not possible. However, an attempt has been made to identify and assign some of the structurally important bands on the basis of the reported infrared spectra of some chalcones [15][16][17]23,26,[49][50][51][52][53][54][55][56] . Some of these like νCH(Aromatic), νC=O, νPh-C=C, Ph-C-C (in plane), δOH (Phenol) and νC-O (Phenol) are in good agreement with the reported values 16,17,26,55 .…”

“…Thus in infrared spectroscopy [52][53][54] , conjugation of ethylenic double bonds, or a carbonyl group and double bonds causes a shift from normal position to a longer wavelength. The unconjugated carbonyl group in acetone shows a band at 1718 cm -1 , while conjugation with one phenyl group, as in acetophenone as stated above lowers the frequency to 1685-1687 cm -1 and conjugation with two phenyl groups, as in benzophenone further lowers the frequency to 1655cm -1 .…”