cis-Bromierung von Alkinen ohne kationische Zwischenstufen

Time-Resolved Photochemistry of Stiffened Stilbenes

Broadband transient absorption spectroscopy is used to study the photoisomerization of stiffened stilbenes in solution, specifically E/ Z mixtures of bis(benzocyclobutylidene) (t4, c4) and ( E)-1-(2,2-dimethyltetralinylidene)-2-2-dimethyltetraline (t6). Upon excitation to S

Single-electron self-exchange between cage hydrocarbons and their radical cations in the gas phase.

We show that the radical cations of adamantane (C(10)H(16)(*+), 1H(*+)) and perdeuteroadamantane (C(10)D(16)(*+), 1D(*+)) are stable species in the gas phase. The radical cation of adamantylideneadamantane (C(20)H(28)(*+), 2H(*+)) is also stable (as in solution). By using the natural (13)C abundances of the ions, we determine the rate constants for the reversible isergonic single-electron transfer (SET) processes involving the dyads 1H(*+)/1H, 1D(*+)/1D and 2H(*+)/2H. Rate constants for the reaction 1H(*+)+1D 1H+1D(*+) are also determined and Marcus' cross-term equation is shown to hold in this case. The rate constants for the isergonic processes are extremely high, practically collision-co…

Thermal Rearrangements of Perchlorohexatrienes-Structures and Experimental and Theoretical Evaluation of Pathways to Isomerization and Cyclization

We have prepared trans- (1) and cis-octachloro-1,3,5-hexatriene (2) by known routes and studied their thermal behavior experimentally and theoretically by ab initio calculations. The three double bonds in 1 and 2 are completely decoupled due to steric hindrance by the eight Cls, as indicated by calculations as well as the single-crystal X-ray structure of 1. The cis isomer 2 can be isomerized to the trans isomer 1 by heating it to 220–250 °C either neat or dissolved in high-boiling solvents, leading to a roughly 2:1 mixture of trans and cis isomers. Calculations at several different levels of theory predict 1 and 2 to be isoenergetic within 2 kJ mol–1. Unimolecular cis/trans isomerization i…

cis-bromination of alkynes without cationic intermediates