The Effects Of Solvents And Charge-transfer On Fermi Resonance

Fermi resonance is a common and important phenomenon that widely exits in infrared spectra and Raman spectra etc. Fermi resonance can occur when a fundamental vibrational level F+0 is close to an overtone (or combination) vibrational level F-0. This process leads to the appearance of two new vibrational levels, F+ and F-, and the original levels are substituted. Frequency shift and energy transfer are invloved in Fermi resonance. The investigation of Ferimi resonance not only has great theoretical significance in some physics field, such as molecular electronic state, vibration and dynamic interaction, but also has important applications in material, biology, and assignation of spectra. Complex is a kind of compound that has complex structure and wide range of applications. In the last twenty years, complex chemistry as one of the most active subjects in the field of modern chemical infiltrate into organic chemistry, polymer chemistry, physical chemistry and biochemistry, has formed many new marginal disciplines. Therefore, we can understand the nature of the formation of complex more clearly by studying the effects of complex on Fermi resonance. This is important to clarify the assignation of complex spectra and the change of spectra intensity.We did the following studies, and have obtained some valuable results: study the change of vibationa frequency of C=O in solvents was inverstigated by the method of solvent variation. We variated and compared some models of solvent effects and then found out the best model which accords with the experimental results. These results have important practical value for determining the vibration frequency in solvents. The function of the dielectric constants of solvents and the intensity ratio of Fermi resonance was obtained, through the analysis of the Fourier transform infrared spectra of p-benzoquinone in solvents. This is first time to combine the solvent dielectric constant and Fermi resonance. The condition of formation of complex was studied, and developed continuous variation method was employed to confirm the ratio of p-benzoquinone and amino acids in the interaction. By comparing the spectra of p-benzoquinone and that of the complex, we investigated the effects of charge-transfer on Fermi resonance.There are three parts in this paper, as follow:partⅠ: Investigation on the change of frequency shifts of tetramethylurea`s C=O. Figure 1 Shifts of C=O vs. KBM parameter Figure 2 Shifts of C=O vs. ANRaman spectra of 1, 1, 3, 3-tetramethylurea in 20 solvents were obtained to investigate the solute-solvent interactions and the spectra can correlate solvent properties such as the Kirkwood-Bauer-Magat (KBM) equation, the solvent acceptor number (AN) and the linear solvation energy relationships (LSER), with the Raman shifts of carbonyl group respectively. There is little linear relation between dielectric constants and the Raman shift. These solvents ware divided into two sections according to the acceptor number. These two sections exhibit good correlation with AN, respectively. Line A:νA= -0.34AN+1644.57 R2=0.932 SD=0.346 Line B:νB= -1.22AN+1663.69 R2=0.976 SD=1.306These frequencies show a better correlation with LSER than the solvent AN. How the solvents interacts with the C=O can be obtained from the regression coefficients.ν(C=O)=(1666.03±0.89)+(-23.11±1.23)α+(-4.87±1.26)β+(-21.83± 1.30)π*+(-1.95±0.64)δR2=0.986 SD=1.469Figure 3 the change of shifts of C=O with the ratio of H2O and TMU Under the influence of special interactions (hydrogen band) and steric hindrance of the associated water molecule, when the ratio of water and TMU is lower than 2, the frequency changes of stretching vibration of carboxyl in TMU is linear proportion to this ratio. But when this ratio is larger than two, the frequency of stretching vibration of carboxyl is a constant at 1585 cm-1. Under the influence of non-special interactions of solvent effects, other vibration frequency change is small.PartⅡ: The relation of intensity ratio of p-benzoquinone and the dielectric constants of solvents.The method of solvent variation is one of the main methods to study Fermi resonance. FT-IR spectroscopy is used to study the Fermi resonance of p-benzoquinone in thirteen solvents. The results show that there are some function relationships between the dielectric constant of solvent and the intensity ratio of Fermi resonance. And the empirical formula is obtained by curve fitting: R=0.40+0.66/ (ε-1.93)The equation of Kirkwood-Bauer-Magat is applied to the study of Fermi resonance. And we obtain the relation between the intensity ratio R and the dielectric constantε. This result is accordance with the empirical formula. In order to confirm our result, the Infrared data of R. A. Nyquist and J. K. Seehra are analyzed. These results are in accord with that of p-benzoquinone: R=0.37+3.60/ (ε-1.50) and R=0.68+0.78/ (ε-1.76) PartⅢ: The effects of charge-transfer on Fermi resonance the effect of pH value on the products. The pH value and the mixed time after which the spectrum was obtained are as follows: (a) pH≈7, t=30 min; (b) pH≈8, t=5 min; (c) pH≈11, t=5 min; (d) pH≈12, t=0 min; (e) pH≈12, t=30 min. The concentrations of PBQ and proline are all 1×10-4 M. We have investigated the effects of pH on the interaction of PBQ and proline with spectroscopy. With the change of pH, there are three different products: charge-transfer complex, semiquinone radical anion and substituted quinone. The composition of the complex has been determined with improved continuous variation method. And we have discussed the mechanism of formation of benzosemiquinone radical anion under condition of strong alkaline.Comparing the spectra of PBQ to that of complex, all peaks shift to high wavelength. For 1159 and 1153 cm-1, there is little change. For 1685 and 1655 cm-1, there is much change on the intensity ratio. This may be attributed to the charge-transfer. When charge donation occurs from a non-bonding molecular orbital located mainly on the nitrogen atom of the donor to aπanti-bonding orbital of the quinone, the force between atom C and oxygen increases. So the frequency of carboxyl shifts to high wavelength. For C-C, the effect of charge-tranfer is slight, because these two atoms C locate in the quinone ring. The vibration structure of polyatomic molecule is a very compliacted system, containing complicate interactions. Fermi resonance is one of the the main coupling phenomenon. It is important to study Fermi resonance for understanding the interaction of vibration energy levels and assigning vibration spctra.