Structure – property relationship for the fluorinealcanes

Abstract

The enthalpy of formation (ΔfH0) of molecules CH3-(CH2)n-CH2F, where 3≤n≤5, CH3-(CH2)n-CHF2 (3≤n≤4), CH2F-(CH2)3-CH2F, CHF2-(CH2)3-CHF2, CF3-(CH2)3-CHF2, CF3-(CH2)3-CF3, CHF2-(CH2)3-CH2F, CF3-(CH2)3-CH2F, fluorinated isobutane C4HmFk, where 0≤m≤9, k = 10-m, and neopentane C5HmFk, where 0≤m≤11, k = 12-m has been calculated by the G4 method. Within the ΔHf0 for molecules of fluoroethanes, fluorobutanes, and fluoropropanes this values has been formed learning sample, which totally includes 180 values. The calculation scheme for the enthalpy of formation of fluorine-containing molecules M have been proposed: ΔHf0add(M) = ΔHf0(R) + a∙ΔHf0(F-F)1,2 + b∙ΔHf0(F-F)1,3 + c∙ΔHf0(F-F)1,4, where ΔHf0(R) is contribution of group R into the enthalpy of formation (R = СH3, CH2, CH, С, CH2F, CHF2, CF3, CHF, CF2, CF), ΔHf0(F-F)1,2, ΔHf0(F-F)1,3, ΔHf0(F-F)1,4 are contributions of interaction of two fluorine atoms, which bounded with the carbon atoms from one, two and three С-С bounds, respectively, a, b, c are numbers of fluorine-fluorine interactions from one, two and three С-С bounds, respectively. All the group contributions have been computed. The comparison have been shown that new scheme is more effective than the simple group-additive methods.

Keywords

• structure – property relationship
• thermodynamic properties
• additive model
• electron structure
• enthalpy of formation
• quantum theory of atoms in molecules
• electron density
• fluorine alkanes
• isobutene
• neopentane