Conjugative Stabilization in an “Antiaromatic” System: The Conformational Mobility of 1,5-Bisdehydro[12]annulene

The isodynamical interconversion between the quasiplanar equilibrium conformers 1b and 1c of 1,5-bisdehydro[12]annulene requires a free energy of activation ΔG^# = 4.5 ± 0.2 kcal/mol (120 K) which was determined by line shape analysis of its temperature-dependent NMR. spectrum. Force field calculations indicate that this barrier reflects the energy needed to disrupt the cyclic π-conjugation in going to the nonplanar transition state 1a .     

Photochemical Ring Slippage of Bis(pentafluorophenyl)titanocene: Reaction kinetics and matrix isolation of the primary photoproduct

Laser flash photolysis and matrix-isolation techniques were applied to elucidate the photochemistry of the orange complex bis(pentafluorophenyl)titanocene ( = bis(η⁵-cyclopentadienyl)bis(pentafluorophenyl)titanium- (IV), Cp₂Ti^IV{C₆F₅}₂, Cp = η⁵-C₅H₅, 1 ) which is used as a polymerization photo-initiator. The primary photo-reaction of 1 is the formation of a highly reactive blue isomer X with unit quantum yield. In carefully dried and degassed benzene solution, the photoisomer X rearranges to starting material 1 with a first-order reaction, k = 5 · 10³ s^?1 at room temperature. X is highly reactive towards H₂O, MeOH, acetone, MeCN, MeNO₂, butane-1,4-diyl diacrylate, 2,2,6,6-tetramethylpiperidine N-oxide, CO, O₂, and N₂; absolute bimolecular rate constants range from 10⁶ to 10⁹ M ^?1 · s^?1. The primary photoisomerization 1→X is tentatively ascribed to a cyclopentadienyl ring slippage from η⁵ to a lower hapticity, a process that opens up coordinative unsaturation.     

Classical microscopic calculation of fast heavy-ion collisions

We consider heavy-ion collisions with beam energies of a few hundred MeV/nucleon, because such collisions seem favorable for producing compressed nuclear matter. As an alternative to hydrodynamic ways of calculating such collisions, we are investigating a microscopic, rapid (and therefore economical) simulation method. There are two simplifications basic to this method: (i) using classical particle kinematics, and (ii) taking nucleonnucleon interactions into account via cross sections rather than explicit forces. Some other simplifications, concerning nuclear binding etc., are presently crude but will be improved. Even at normal density, nuclear matter is not so dilute; therefore our calculations show some sensitivity to details of the mechanism assume for nucleon-nucleon scattering. For head-on collision of two mass-235 nuclei, our present calculations yield maximum densities between 2 and 3 times that of normal nuclear matter.     

Photolysis and Pyrolysis of N-Methyl Isoindole

Near UV. irradiation of N-methyl isoindole ( 1 ) in deaerated solution has yielded two constitutionally isomeric [_π4_s+_π4_s] dimers 3 and 4 (Scheme 2). No transient or stable photoisomers of 1 were detected. The photodimers were reconverted to 1 both by pyrolysis and photolysis. The photocleavage of dimer 3 proceeds (predominantly) by anonadiabatic pathway yielding 1 in its electronic ground state. Prolonged pyrolysis of 1 afforded 11H-indeno [1,2-c]-isoquinoline ( 5 ) as a major product.     

Schnitt- und Zykelgeometrien

Ohne ZusammenfassungHabilitationsschrift Darmstadt 1975.     

Eine Charakteristische Spiegelungseigenschaft hermitescher Quadriken

If is a projective space of dimension 3 and characteristic 2 and a semi ovoid of, then is a non degenerate semi quadric and is of finite dimension, if and only if there exists a perspectivity of order 2 and axish stabilizing, for every hyperplaneh meeting in at least 2 points.