Concentration dependent wavenumber shifts and linewidth changes of some prominent vibrational modes of C4H8O investigated in a binary system (C4H8O+H2O) by polarized Raman study and ab initio calculations

Acid–base interactions between formamide and tetrahydrofuran molecules: Raman investigation of speciation in a binary system of biological interest

“…2 However, the assignment of this band as belonging to the C-O symmetric stretching vibration of the Lewis acid-base adduct is today out of discussion. 5,24 As can be seen in Table 1, the n FA -THF values decrease with the increase of FA concentration and this is a behavior expected of real solutions. However, a simple extrapolation of n FA -THF data to zero concentration allows us to interpret the FA-THF adduct formation in the limit of infinite dilution.…”

“…The former, which is more intense and sharp, corresponds to the C-C stretching mode whereas the second, which is less intense and broad, corresponds to the C-O stretching mode. 5 The addition of FA leads to the appearance of a third band located at 897 cm 1 , whose intensity increases with increasing the concentration of this solvent. Figure 1 illustrates Raman spectra of the binary solvent mixtures and as can be seen, when the FA concentration increases from 5.0 to 20.0 M, the bands at 915 and 910 cm 1 suffer a reduction of intensity and it is worth noting that the first band is more sensitive than the second.…”

“…23 Additionally, the oxygen atom of this molecule is commonly assigned to its basic site. 5 In contrast, the active protons (or high acceptor number) of FA are responsible for its preferential interaction with anions or other molecules containing a donor atom. 9,10 Based on these data, we can perfectly conclude that the spectral variations observed for the binary solvent mixtures are consistent with our interpretation, where the C-O and NH 2 groups are preferentially affected.…”

“…9,10 Based on these data, we can perfectly conclude that the spectral variations observed for the binary solvent mixtures are consistent with our interpretation, where the C-O and NH 2 groups are preferentially affected. Recently, Ojha et al 5 investigated the H 2 O/THF system by means of Raman spectroscopy and ab initio calculations. Their results are in excellent agreement with ours, where a band observed at 896 cm 1 has been assigned to the hydrogen bonded complex, C 4 H 8 O-HOH.…”

“…7 -11 Most of these reactions result in 1 : 1 stoichiometry, 7,8,12 -14 but one cannot assume this a priori and other adducts might also be present. 5,15 Traditionally, IR and Raman spectroscopies have been used as basic experimental techniques for these studies because of the shifts in wavenumbers induced by the hydrogen bonding. Particularly, our research group is also interested in quantitative Raman experiments to determine the number of molecules interacting with FA in the inner sphere of solvation.…”