Alkenes from terminal epoxides using lithium 2,2,6,6-tetramethylpiperidide and organolithiums or grignard reagents

E-Alkenes (including arylated alkenes, dienes, and allylsilanes) are efficiently prepared by alpha-deprotonation of terminal epoxides using lithium 2,2,6,6-tetramethylpiperidide, followed by in situ trapping with organolithiums or Grignard reagents.     

Energy disposal during desorption of D2 from the surface and subsurface region of Ni(111)

The recombination of surface and subsurface D atoms on Ni(111) has been studied using resonance-enhanced multiphoton ionisation (REMPI) to measure the internal state and translational energy distributions of the desorbing product. By detecting D2 formed during temperature-programmed desorption we were able to examine the reaction between subsurface and surface D atoms, and the recombination of two D atoms chemisorbed on the surface. Translational energy distributions for D2 formed by recombination of surface D are very sensitive to coverage. Desorption from a low coverage surface produced a translational energy release of 2.6 kT, but a thermal rotational distribution, reflecting an entrance channel barrier to dissociative chemisorption on the clean Ni(111) surface. Sticking probabilities predicted from detailed balance are consistent with molecular beam adsorption measurements. Desorption from D coverages above 0.5 ML resulted in a sub-thermal energy release, desorption being mediated by a molecular precursor state with D2 dissociation occurring via a non-activated, trapping-dissociation channel. In contrast, the reaction of subsurface D produces translationally hot D2, with a mean energy approaching 8 kTs at 180 K. This is consistent with the energetics for direct recombination of a chemisorbed D atom with a metastable subsurface D atom, which overcomes an activation barrier to resurface of between 0.35 and 0.47 eV depending on D concentration. The energy release decreases at higher temperature, probably as a result of a reduction in the energy of resurfacing D as the subsurface D concentration drops. This low energy component is attributed to accommodation of resurfacing D which is unable to react directly, followed by slow thermal desorption via the high coverage, surface D recombination channel. No internal rotational or vibration excitation was found in D2 formed by reaction of subsurface D.     

Ray-tracing evaluation of empirical models for predicting noise in industrial workshops

To evaluate the accuracy of empirical models for predicting steady-state noise levels and reverberation times in typical industrial workshops, predictions by these models were compared with predictions by a ray-tracing model, nominally using the same input data. Comparisons were made for three workshops—‘long’, ‘flat’ and ‘quasi-cubic’ in shape—with reflective and absorbent ceilings, when empty and with four densities of fittings. In the case of the ‘long’ room, noise levels were predicted along both the long and short major horizontal axes. In ‘long’ and ‘flat’ workshops, steady-state prediction by the empirical models often agreed with ray-tracing prediction within 2 dB. This result suggests that the empirical models are fundamentally valid. However, agreement was worse at large source/receiver distances, and at 500 Hz. Empirical reverberation-time prediction generally agreed less well with ray tracing, possibly indicating that the empirical reverberation-time prediction models are less valid. Strong disagreement occurred between the models in the case of steady-state prediction in the ‘quasi-cubic’ workshop, indicating that the empirical steady-state models are invalid in this case. Agreement for reverberation time was good with a non-absorbent ceiling, but poor with an absorbent ceiling.