Influence of Molecular Parameters on Rate Constants of Thermal Dissociation/Recombination Reactions: The Reaction System CF4 ⇄ CF3 + F.

The possibilities to extract incompletely characterized molecular parameters from experimental thermal rate constants for dissociation and recombination reactions are explored. The reaction system CF4 (+M) ⇄ CF3 + F (+M) is chosen as a representative example. A set of falloff curves is constructed and compared with the available experimental database. Agreement is achieved by minor (unfortunately not separable) adjustments of reaction enthalpy and collisional energy transfer parameters.

The Thermal Dissociation-Recombination Reactions of SiF4, SiF3, and SiF2: A Shock Wave and Theoretical Modeling Study.

Monitoring UV absorption signals of SiF2 and SiF, the thermal dissociation reactions of SiF4 and SiF2 were studied in shock waves. Rationalizing the experimental observations by standard unimolecular rate theory in combination with quantum-chemical calculations of the reaction potentials, rate constants for the thermal dissociation reactions of SiF4, SiF3, and SiF2 and their reverse recombination reactions were determined over broad temperature and pressure ranges. A comparison of fluorosilicon and fluorocarbon chemistry was finally made.

Shock wave and modeling study of the reaction CF4 (+M) ⇔ CF3 + F (+M).

The thermal decomposition of CF4 (+Ar) → CF3 + F (+Ar) was studied in shock waves over the temperature range 2000-3000 K varying the bath gas concentration [Ar] between 4 × 10(-6) and 9 × 10(-5) mol cm(-3). It is shown that the reaction corresponds to the intermediate range of the falloff curve. By combination with room temperature data for the reverse reaction CF3 + F (+He) → CF4 (+He) and applying unimolecular rate theory, falloff curves over the temperature range 300-6000 K are modeled. A comparison with the reaction system CH4 (+M) ⇔ CH3 + H (+M) is made.

Synthesis of chiroptical molecular switches by pd-catalyzed domino reactions.

New photochromic switches based on helical alkenes can quickly and efficiently be accessed by Pd-catalyzed domino reactions using a modular approach; this allows a wide variability in product formation with the advantages of a convergent synthetic route. The alkenes have been synthesized in excellent enantioselectivity and their switching properties assessed by stimulation with nanosecond laser pulses at two different wavelengths in over 1000 switching cycles.