The thermodynamic properties of alkylated γ-lactones

Abstract

In this work, we performed a complex study of the thermodynamic properties of three alkylated γ -lac- tones. We determined their enthalpies of combustion and formation, measured vapor pressures and found the enthalpies of vaporization, and studied their conforma- tional state. The spectral and molecular data were used to calculate the thermodynamic properties of γ -pen- tanolactone ( I ), γ -hexanolactone ( II ), and γ -nonanolac- tone ( III ). Abstract —The enthalpies of formation of γ -pentanolactone ( I ), γ -hexanolactone ( II ), and γ -nonanolactone ( III ) were determined by combustion calorimetry. The enthalpies of vaporization of these lactones were mea- sured by the transfer method. Conformational analysis was performed and equilibrium structures, sets of fun- damental vibrations, moments of inertia, and total energies of the stablest conformers of I , II , and III were cal- culated by the B3LYP/6-311G( d , p ) , G3MP2, and CBS-QB3 methods. The experimental IR spectra and calcu- lated vibrational frequencies were used to obtain sets of fundamental vibrations of the stablest conformations. The thermodynamic properties of I - III in the ideal gas state were determined over the temperature range 0- 1500 K. Additive and quantum-chemical methods were applied to estimate the ∆ f H ° (g) values of a number of γ -lactones. Composite quantum-chemical methods were used to obtain the energies of monomethyl γ -butyro- lactones and estimate their relative stability depending on the position of the methyl substituent in the ring.