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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 26, Number 8
BKCSDE 26(8)
August 20, 2005 

The Positional Effect of Solute Functional Group among Positional Isomers of Phenylpropanol in Hydroxyl Group-Solvent Specific Interactions in Methanol/Water Mixed Solvents Monitored by HPLC
Won Jo Cheong*, Joung Ho Ko, Gyoung Won Kang
Phenylpropanol, Hydroxyl group, Positional effect, Specific interaction
We have evaluated the hydroxyl group-solvent specific interactions by using a Lichrosorb RP18 stationary phase and by measuring the retention data of carefully selected solutes in 50/50, 60/40, 70/30, 80/20, and 90/10(v/v%) methanol/water eluents at 25, 30, 35, 40, 45, and 50 oC. The selected solutes are 3 positional isomers of phenylpropanol, that is, 1-phenyl-1-propanol, 1-phenyl-2-propanol, and 3-phenyl-1-propanol. There exist clear discrepancies in ΔHo (solute transfer enthalpy from the mobile to the stationary phase) and TΔSo (solute transfer entropy) among positional isomers. The difference in ΔHo and TΔSo between secondary alcohols (1- phenyl-1-propanol and 1-phenyl-2-propanol)is negligible compared to the difference between the primary alcohol (1-phenyl-3-propanol) and secondary alcohols. The TΔSo values of 3-phenyl-1-propanol are close to those of butylbenzene while the TΔSo values of secondary alcohols are close to those of propylbenzene. The difference in ΔΔHo (specific solute-mobile phase interaction enthalpy) between the primary alcohol and the secondary alcohol decreases with increase of methanol content in the mobile phase. A unique observation is an extremum for 1-phenyl-3-propanol in the plot of TΔΔSo vs. methanol volume %. The positive sign of TΔΔSo of 3-phenyl-1-propanol implies that the entropy of 3-phenyl-1-propanol is greater than that of the hypothetical alkylbenzene (the same size and shape as phenylpropanol) in the mobile phase.
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