Homolytic reactions of polyfluoroaromatic compounds. Part XII. Aryldehydrogenation and aryldefluorination in polyfluorobenzenes

The thermal decomposition of benzoyl peroxide in a range of polyfluorobenzenes at 80° gives biaryls arising from both the displacement of fluorine and hydrogen. Phenyldefluorination predominated only in the attack of 1,2,3,4-tetrafluorobenzene and of pentafluorobenzene, but was evident even in the attack of $\text{o}$-difluorobenzene. The relative rates of displacement, as shown by the isomer distributions, were generally well reflected by the application of partial rate factors found in the phenylation of fluorobenzene; however, phenyldefluorination was not so easily amenable to this treatment, a possible consequence of complex formation between radical precursor and substrate.     

Assessment of pulmonary artery pulse wave velocity in children: An MRI pilot study

Purpose

To assess the feasibility of measuring pulmonary artery (PA) pulse wave velocity (PWV) in children breathing ambient air and 12% oxygen.

Methods

Velocity-encoded phase-contrast MR images of the PA were acquired in 15 children, aged 9–12 years, without evidence of cardiac or pulmonary diseases. PWV was derived as the ratio of flow to area changes during early systole. Each child was scanned twice, in air and after at least 20 minutes into inspiratory hypoxic challenge. Intra-observer and inter-observer variability and repeatability were also compared.

Results

PA PWV, which was successfully measured in all subjects, increased from 1.31 ± 0.32 m/s in air to 1.61 ± 0.58 m/s under hypoxic challenge (p = 0.03). Intra- and inter-observer coefficients of variations were 9.0% and 15.6% respectively. Good correlation within and between observers of r = 0.92 and r = 0.72 respectively was noted for PA PWV measurements. Mean (95% limit of agreement) intra- and inter-observer agreement on Bland–Altman analysis were − 0.02 m/s (− 0.41–0.38 m/s) and -0.28 m/s (− 1.06–0.49 m/s).

Conclusion

PA PWV measurement in children using velocity-encoded MRI is feasible, reproducible and sufficiently sensitive to detect differences in PA compliance between normoxia and hypoxia. This technique can be used to detect early changes of PA compliance and monitor PAH in children.     

Retarded dielectric theory of electron energy loss in multilayers and superlattices

This work uses computer algebra to develop the dielectric theory of energy loss for fast electrons travelling in multilayer systems and superlattices. The interaction of a relativistic electron beam is analysed in detail for beams travelling normal or parallel to the interfaces.     

Fundamental photochemical approach to the concepts of fluence (UV dose) and electrical energy efficiency in photochemical degradation reactions

For photochemical reactions in a quasi collimated beam, derivations are presented that introduce 'rate constants' based on the fluence (UV dose) received within the irradiated solution. These fluence-based 'rate constants' are shown to be fundamental and depend only on the quantum yield and the molar absorption coefficient at the irradiation wavelength. An experimental example is given, where the quantum yield for the photolysis of atrazine is determined to be 0.033. The new concepts are developed further to analyze the Figure-of-Merit Electrical Energy per Order (E _EO), and it is shown that the E _EO depends on the same fundamental photochemical parameters. An example of the photolysis of N-nitrosodimethylamine (NDMA) is presented, and it is shown that the E _EO should decrease (increased electrical energy efficiency) as the radius of the UV reactor increases (increased path length), and should increase as the percent transmittance of the water decreases.     

Nucleophilic displacement in polyhalogenoaromatic compounds. Part X. Transmission of substituent effects in polyfluorobiphenyl derivatives

The rate of methoxydefluorination (NaOMe-MeOH, 323.2 K) and the ¹⁹F-NMR chemical shifts of some substituted penta- and nona-fluorobiphenyls have been measured. The observed substituent effects parallel those found in the corresponding pentafluorobenzenes and demonstrate proportionate transmission of the total substituent electronic effect across the aromatic system.     

Nucleophilic displacement in polyhalogenoaromatic compounds. Part V. Fluorodechlorination of 1,2,3,4- and 1,2,3,5-tetrachlorobenzenes and 2,3,4,5,6-pentachlorotoluene in sulpholan

Potassium fluoride in sulpholan (tetramethylene sulphone) reacted readily with 1,2,3,4- and 1,2,3,5-tetrachlorobenzenes at 250°, but needed temperatures of 270° before fluorodechlorination of pentachlorotoluene proceeded readily. Individual rate constants for the formation and decomposition of some of the fluorochloroarenes have been isolated; their values are discussed in terms of the electronic effects of the substituents.