Browsing by Author "Kao, Dah-Yu"

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IR Study of Monomer-Dimer Self-association of 2,2-Dimethyl-3-ethyl-3-pentanol in n-Octane: Determination of the Molar Absorptivities of Monomer and Dimer Bands, and Dimerization Constants Using Novel Equations
(2013-12-01)
Chen, Jenn-Shing
;
Yeh, Kwei-Tin
;
Wu, Cheng-Chang
;
Kao, Dah-Yu
;
應用化學系
The monomer-dimer self-association equilibrium of 2,2-dimethyl-3-ethyl-3-pentanol in n-octane has been studied by IR spectroscopy at four temperatures (288, 298, 308, and 318 K). The solute was chosen to restrict the self-association between solute molecules to dimerization only, owing to steric hindrance of the bulky chains in the vicinity of the OH group. Two linear equations have been derived for the treatment of the experimental data. One of these equations was used to treat the data of the concentration dependent integrated absorbance of the monomer bands for each temperature to obtain the monomer molar absorptivity, epsilon (m), and dimerization constant, K. The other equation was used to treat the data of concentration-dependent dimer bands to obtain the dimer molar absorptivity, epsilon (d), and K. Thus, the dimerization constant was determined by two methods. Since the same thermodynamic quantity K is obtained from either the monomer bands or the dimer bands, the difference between them at a given temperature can serve as an assessment of the quality of the experiment. The standard enthalpy and entropy of dimerization were also obtained from a van't Hoff plot.
Toward a Better Determination of Infrared Molar Absorptivities and Dimer Formation Constants in Self-association Through Hydrogen Bonding: 3-Ethyl-2-methyl-3-pentanol in Tetrachloroethylene as an Example
(2017-10-01)
Chen, Jenn-Shing
;
Yeh, Kwei-Tin
;
Kao, Dah-Yu
;
Baird, James K.
;
應用化學系
The monomer-dimer self-association of the dilute 3-ethyl-2-methyl-3-pentanol in tetrachloroethylene in the very dilute state was studied by infrared spectroscopy at several temperatures. The solute was deliberately chosen so that higher oligomers were suppressed by the steric hindrance arising from bulky groups on both sides of hydroxyl group. Two linear utility equations were derived to treat, respectively, the integrated absorbance of the monomer band, A(m), and of the dimer band, A(d), as functions of the initially prepared solute concentration, [B](0). The respective molar absorptivities were obtained by fitting these equations to the data. Unlike previous methods, the dimerization constant (K) can be obtained from either A(m) or A(d). Any discrepancy between these two values of K serves as a measure of the quality of the data. The values of K at different temperatures were employed to calculate the standard enthalpy and entropy of dimerization by using a van't Hoff plot. The dimer is predominantly in the cyclic form where both hydroxyl protons are hydrogen-bonded. This is inferred from the following observations: (1) the spectrum displays only two bands between 3300 and 3750 cm(-1); (2) the constancy of A(d)/A(m)(2) as a function of [B](0); and (3) the linearity of both plots [B](0)/A(m) vs. A(m), and [B](0)/A(d) vs. A(d)(2).