ChemInform Abstract: Statistical Analysis of Electronic Absorption Spectra of Pyrazoles. Part 2. N‐Methylpyrazoles and N‐Unsubstituted Pyrazoles with Different Substituents at Positions 3 and 5

Cativiela, Carlos; Lafuente, J.; Laureiro, José Ignacio García; Elguero, J.

doi:10.1002/chin.198925038

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“…The FreeWilson matrix had thus five columns for the five explanatory variables n, and 10 lines for 10 methoxybenzoic acids including benzoic acid itself. The leastsquares solution [24,25] was carded out [26] with standard programs for multiple linear regression. Using the method of ascending regression, we started the regression with noM~, then added no~tho and the further terms in a successive fashion.…”

Section: Additive Relationshipsmentioning

confidence: 99%

Enthalpies of formation of methoxybenzoic acids and their dependence on structure

et al. 1996

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The energy of combustion of 2,5-dimethoxybenzoic acid has been determined using a static bomb calorimeter. The vapor pressures of the compound have been measured over a 18 K temperature interval by the Knudsen effusion technique. Heat capacity measurements between T = 270 K and T = 338 K were carded out by DSC, From these experimental results the standard molar enthalpies of combustion, sublimation, and formation in the crystalline and gaseous state at the temperature 298.15 K have been derived. With this compound, the series of mono-and dimethoxybenzoic acids have been completed. TheirAfH~, values were expressed by an additive relationship, taking into account the number of methoxy groups and the number of all 1,2 interactions: an accuracy of 3.3 kJ.mol -) was achieved. In an alternative approach the substituent effect of the methoxy groups was evaluated within the framework of isodesmic reactions. The effect of disubstitution was referred to mono derivatives and the excess energy--the so-called buttressing effect--was evaluated (2-24 kJ'molS ~ for individual bis derivatives). These values were explained in terms of the conformation of the methoxy group around the C~r--O bond.

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Section: Additive Relationshipsmentioning

confidence: 99%