The stereochemistry of sigmatropic rearrangements. Tests of the predictive power of orbital symmetry rules

QSPR correlation equations were developed for the prediction of the solubilities of organic gases and vapors in water. A two-parameter correlation with the squared correlation coefficient R2 = 0.977 gives excellent predictions for 95 alkanes, cycloalkanes, alkenes, alkylarenes, and alkynes. A satisfactory description (R2 = 0.941) of the gas solubilities of 406 organic compounds with a large structural variablity was obtained using a five-parameter QSPR equation. Notably, all the parameters involved in these equations can be derived solely from the chemical structure of the compounds which makes them very useful for the prediction of the solubilities of unknown or unavailable compounds.

A qspr study of the solubility of gases and vapors in water

Publisher Summary This chapter discusses the thermal pyrolyses of a number of strained ring compounds. In most of the cases considered, there is good evidence that the processes are unimolecular. Plausible transition complexes and reaction paths are suggested in the chapter, which are based on the consideration of such factors as the kinetic parameters, stereochemistry of the reaction, and effect of substituents. In reactions of this type, the description of the transition complex is fraught with difficulties, since the absences of such things as solvent effects, which can be helpful in bimolecular reactions, limit the criteria. Often two types of transition complex may be equally good at accounting for the observed data. Sometimes, one complex will explain some of the data, while another is better able to account for the remainder. It is probable that in many cases the representation of the transition complex is too simple, biradical compared with expanded ring in the cyclopropane isomerizations, and that the true situation lies between the extremes, in exactly the same way as the simple Kekule formula do not represent all the properties of benzene.

The Gas Phase Pyrolyses of Some Small Ring Hydrocarbons

Paramagnetically induced relaxation effects of O2 and the nitroxide 4-hydroxy TEMPO were measured for the amide protons of perdeuterated rubredoxin from the hyperthermophilic archaeon Pyrococcus furiosus and the mesophilic bacterium Clostridium pasteurianum For both O2 and the impermeant nitroxide, the induced relaxation at the static solvent inaccessible amide sites is dominated by long-range interactions with the paramagnetic species in the bulk aqueous phase The upper bound of O2 solubility in the internal matrix of the rubredoxins is one-tenth that of the bulk aqueous phase Furthermore, the difference between the oxygen solubilities inside the two rubredoxins is at most 1% that of bulk water O2 solubility, suggesting that there are only modest differences in this measure of fluidity for the mesophile vs hyperthermophile protein interiors Calculations based on the assumption of a paramagnet uniformly distributed on the protein exterior yield accurate predictions at nearly all amide sites for the mi

O2 penetration and proton burial depth in proteins: applicability to fold family recognition.

The gas phase reaction of iodine (2.8–43.3 torr) with methyl ethyl ketone (MEK) (7.4–303.4 torr) has been studied over the temperature range 280–355°C in a static system. The initial rate of disappearance of I2 is first order in MEK and half order in I2. The rate-determining step is the abstraction of a secondary hydrogen atom by an iodine atom: 






where k1 is given by 






and θ = 2.303RT in kcal/mole. This activation energy is equivalent to a secondary CH bond strength of 92.3 ± 1.4 kcal/mole and ΔH of the methylacetonyl radical = -16.8 ± 1.7 kcal/mole. By comparison with 95 kcal/mole for the secondary CH bond strength, when delocalization of the unpaired electron with a pi bond is not possible, the resonance stabilization of the methylacetonyl radical is calculated to be 2.7 ± 1.7 kcal/mole. This value is 10 kcal/mole less than the stabilization energy of the isoelectronic methylallyl radical. The difference in pi bond energies in the canonical forms of the methylacetonyl radical is shown to account for the variation in stabilization energies.

Maria Zupan

Papers

The kinetics of the thermal decomposition of isopropylcyclobutane1