DTA and dielectric measurements at high pressures of t‐butyl‐bromide

Abstract

ConclusionsThe photochemical generation of peroxy radicals enables the direct determination of rate coefficients of the reaction of these radicals with alcohols.According to Howard, Schwalm and Ingold [ 3 ] secondary peroxy radicals are about 3-5 times more reactive in hydrogen abstraction reactions than tertiary ones. Comparing our results with those of Kroo et al.[lS], who investigdted the reactions of 2-cyano-2-propyl peroxy radicals with I-phenyl ethanol and benzyl alcohol as well, we obtain a factor o f 5 -5.5 at T = 55 C. Our values, however, seem to be somewhat higher than the rate coefficient of the reaction between a-hydroxyl-benzylperoxy radicals and benzyl alcohol measured by Howard and Korcek [8].The temperature dependence of the reaction between 1-phenylethyl peroxy radicals and 1-phenyl ethanol is in very good agreement with the data of Hajdu et al. Oxid. Commun. 6, 371 (1984).J. Chem. Kinet. 18, 31 (1986).( 1 988

Differential Thermal Analysis and Dielectric Studies on 2-Methyl-2-Nitro-Propane under High Pressure

“…Values about unity for g discount specific correlations in TBN, in agreement with previous findings on other tertiary butyl compounds (TBC1 [26] and TBBr [27]), and on cyclohexanone [23]. P,V,T-data [5,17] enable us to distinguish between isochoric temperature changes and isothermal density changes, which is one of the principal advantages of high pressure studies [13].…”

Two-component System CCl4 + (CH3)3CBr: Extrema in Equilibria Involving Orientationally Disordered Phases

“…36 The results are consistent with the high values of the dielectric permittivity from dielectric measurements. 14,26 The birefringence of the uniaxial crystals of phase II was found early 27 and lately measured. 28 As a proof of the orientational disorder of the dipolar axis, an orientational order parameter describing the average over fluctuations of the dipolar axis from a preferred orientation, defined as S ) (1/2)〈3 cos ϑ -1〉, where ϑ stands for the angle between the 3-fold symmetry axis of the molecule and crystal optical axis, was found to vary between 0.038 at 231 K and 0.052 at 210 K 28 or 0.0031-0.0044 in the same temperature range.…”

“…tert- Butyl compounds have stimulated a large number of theoretical studies as well as have been the object of considerable experimental efforts to elucidate the nature of the disorder and, more specifically, the hindrance to the orientational disorder. − …”

From High-Temperature Orientationally Disordered Mixed Crystals to Low-Temperature Complex Formation in the Two-Component System (CH3)3CBr + Cl3CBr

“…Simple tetrahedral methylhalogenomethane (MHM) compounds, (CH 3 ) 4−( m + n ) CX m Y n (X,Y = F, Cl, Br, I, n, m = 0, ... 4), have stimulated a large number of experimental studies as well as have been the object of many theoretical works through molecular dynamics simulations to rationalize the intermolecular interactions and the nature of the orientationally disordered (OD) or plastic phases appearing within the rich polymorphic behavior of such compounds. − It should be emphasized that this set of compounds constitutes a remarkable case study because these molecules have very close size and a limited kind of intermolecular interactions. These characteristics make systematic studies and comparisons possible.…”

“…In the case of pseudospherical-shaped molecules, the orientational order is lost first, giving a phase where molecules are able to reorient on their lattice sites, a phase commonly known as plastic phase, a term which is also used to describe the high-temperature phase existing just before the liquid state . In spite of the similarity in size and intermolecular interactions, the polymorphic behavior within the realm of MHM compounds at normal pressure (i.e., in equilibrium with its vapor pressure), as well as at high pressure, is known to be quite different, a fingerprint that small differences of size and intermolecular interactions finely tune the thermodynamic functions accounting for the stability of the phases. − ,− ,− ,, The stability of the phases can be revealed not only by means of the study of pure compounds, as a function of temperature and pressure, but also by the determination of the phase diagram between two homologous compounds. ,,,− With the last procedure, the formation of mixed crystals provides information on the thermodynamic mixing properties, thus on the interactions between their molecular units and, in some cases, on the intrinsic polymorphic behavior of the pure compounds. , …”