Thermodynamically sick molecules: searching for defective experimental enthalpies of formation values using empirical and quantum chemistry methods

A revised parameterization of the extended Laidler bond additivity method and quantum chemistry calculations were independently used to assess the standard molar enthalpies of formation of 20 non-polycyclic hydrocarbons in the gas phase. The detected discrepancies between predicted and experimental values are discussed, illustrating how this methodology can be useful in curing thermochemical data.     

Recycling of Polyolefins: Part 2: Blends of Several Polymers

Abstract

The aim of the present paper is to study the feasibility of recycling polyolefins with some additives, such as copolymers in order to improve the mechanical properties and increase the useful life of the blends. From analysis of the results of blends of polypropylene(PP) with POD(Blend of recycled Polyolefins), it can be concluded that it is possible to recycle POD up to 20%, the addition of a copolymer to the 12% composition improving the interfacial adhesion. In the case of low density polyethylene(LDPE) mixtures with POD, the optimum improvement in properties is obtained with approximately 10% of POD. The addition of copolymers did not yield any improvement in the properties.     

FT‐Raman,FTIR and density functional theory studies of a hydrogen‐bonded formamide:pyridine complex

Raman and IR experiments have been carried out on formamide (FA) and pyridine (Py) mixtures at different compositions. The appearance of a new Raman band at 996 cm⁻¹ (ν₁ region of Py), whose intensity depends on the FA concentration, is assigned to an FA:Py adduct and this result is in excellent agreement with those of other authors who employed noisy light‐based coherent Raman scattering spectroscopy (I⁽²⁾ CARS). Another band at 1587 cm⁻¹ (ν₈ region of Py) has been observed for the first time by using Raman and IR spectroscopies. Its intensity shows the same dependence on the FA concentration and this fact allows us to also attribute it to an FA:Py adduct. The good relationship between the Raman and IR data demonstrates the potential of the vibrational spectroscopy for this kind of study. Owing to higher absolute Raman scattering cross section, the ν₁ region of Py has been chosen for the quantitative analysis and a stoichiometry of 1:1 FA:Py is reported. The experimental data are very well supported by the density functional theory (DFT) calculation, which was employed for the first time to the present system. Furthermore, the actual investigation shows an excellent agreement with those reported from computational calculations for similar systems. A comparison with our previous studies confirms that the solvent dielectric constant determines the stoichiometry of a given Lewis acid–base adduct in the infinite dilution limit. Copyright © 2009 John Wiley & Sons, Ltd.     

An interpolation problem in the Denjoy–Carleman classes

Inspired by some iterative algorithms useful for proving the real analyticity (or the Gevrey regularity) of a solution of a linear partial differential equation with real-analytic coefficients, we consider the following question. Given a smooth function defined on $[a,b]\subset \mathbb{R}$ and given an increasing divergent sequence $d_n$ of positive integers such that the derivative of order $d_n$ of f has a growth of the type $M_{d_n}$, when can we deduce that f is a function in the Denjoy–Carleman class $C^M([a,b])$? We provide a positive result and show that a suitable condition on the gaps between the terms of the sequence $d_n$ is needed.