Centro de Investigação em Química, Department of Chemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, 687, P-4169-007 Porto, Portugal.
J Phys Chem B. 2010 Jun 17;114(23):7909-19. doi: 10.1021/jp102024y.
The present work reports the thermodynamic study performed on three monofluorinated nitrobenzene derivatives by a combination of experimental techniques and computational approaches. The standard (p degrees = 0.1 MPa) molar enthalpies of formation in the liquid phase of the three isomers of fluoronitrobenzene were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by rotating bomb combustion calorimetry. The vapor pressure study of the referred compounds was done by a static method and, from the obtained results, the phase diagrams were elaborated, and the respective triple point coordinates, as well as the standard molar enthalpies of vaporization, sublimation and fusion, at T = 298.15 K, were determined. The combination of some of the referred thermodynamic parameters yielded the standard (p degrees = 0.1 MPa) molar enthalpies of formation in the gaseous phase, at T = 298.15 K, of the studied compounds: Delta(f)H(m)(o) (2-fluoronitrobenzene, g) = -(102.4 +/- 1.5) kJ x mol(-1), Delta(f)H(m)(o) (3-fluoronitrobenzene, g) = -(128.0 +/- 1.7) kJ x mol(-1), and Delta(f)H(m)(o) (4-fluoronitrobenzene, g) = -(133.9 +/- 1.4) kJ x mol(-1). Using the empirical scheme developed by Cox, values of standard molar enthalpies of formation in the gaseous phase were estimated and afterwards compared with the ones obtained experimentally, and both were interpreted in terms of the molecular structure of the compounds. The theoretically estimated gas-phase enthalpies of formation were calculated from high-level ab initio molecular orbital calculations at the G3(MP2)//B3LYP level of theory. The computed values compare very well with the experimental results obtained in this work and show that 4-fluoronitrobenzene is the most stable isomer from the thermodynamic point of view. Furthermore, this composite approach was also used to obtain information about the gas-phase basicities, proton and electron affinities and, finally, adiabatic ionization enthalpies.
本工作通过实验技术和计算方法的结合，对三种单氟硝基苯衍生物进行了热力学研究。三种氟硝基苯异构体在液相中的标准（p 度=0.1 MPa）摩尔生成焓是由在 T=298.15 K 下，在氧气中进行的标准摩尔燃烧能，通过旋转弹燃烧量热法测量得出的。所涉及化合物的蒸气压研究是通过静态方法进行的，从获得的结果中，绘制了相图，并确定了各自的三相点坐标，以及在 T=298.15 K 下的标准摩尔蒸发焓、升华焓和熔融焓。结合一些参考热力学参数得到了研究化合物在气相中的标准（p 度=0.1 MPa）摩尔生成焓，在 T=298.15 K 时，为：Delta(f)H(m)(o)（2-氟硝基苯，g）=-(102.4 +/- 1.5) kJ x mol(-1)，Delta(f)H(m)(o)（3-氟硝基苯，g）=-(128.0 +/- 1.7) kJ x mol(-1)，和 Delta(f)H(m)(o)（4-氟硝基苯，g）=-(133.9 +/- 1.4) kJ x mol(-1)。使用 Cox 开发的经验方案，估算了气相标准摩尔生成焓，并将其与实验值进行了比较，并根据化合物的分子结构对两者进行了解释。气相标准摩尔生成焓的理论估计值是从 G3(MP2)//B3LYP 理论水平的高精度从头算分子轨道计算中计算出来的。计算值与本工作中获得的实验结果非常吻合，表明从热力学角度来看，4-氟硝基苯是最稳定的异构体。此外，还使用这种组合方法获得了关于气相碱度、质子和电子亲合势以及最终绝热电离焓的信息。
