Atomic orbital calculations, light

In the light of experimental difficulties associated with the identification of intermediates, a MINDO/3 quantum-mechanical study of the singlet state ( a2) of the cyclobutylidene to methylenecyclopropane rearrangement has been carried out. It has been proposed that the whole process is initiated by electrophilic attack from the C3 methylene group of cyclobutylidene at the empty p atomic orbital on the Cl carbene site, so that a shift of electron density towards Cl can take place to give the bicyclobutane-like nonclassical carbene intermediate 4. Finally, the bicyclobutane intermediate 4 undergoes a symmetry-allowed conrotatory bond-fission process to generate methylenecyclopropane. The activation enthalpy calculated for the two steps is 8 kcal mol-1.2... 

The standard extended Huckel Hamiltonian (23) with a minimum basis set of Slater-type atomic orbitals were used in all calculations. The overlap and Hamiltonian matrices were computed for the RC fragment in the light conformation (12), which included Bph Qa Qb, the iron ion and the relevant protein environment Met , Met , His ,... 

The photoelectron intensity I (with the detector being at infinity) for atomic orbitals which are excited by linearly polarized light can be calculated via the differential cross section daldQ, [6] ... 

To understand the ES interactions between the PSB and protein environment in more detail, the ESP at the retinal backbone atoms was calculated. The calculated ESP was strongly negative on the Schiff base side (N side) primarily because of a glutamate that served as the counterion to the PSB. The contributions of the other amino acids were also important, as described later in this manuscript. The amount of the ESP decrease grows in the order of HR, HG, Rh, and HB, which correlates with the observed spectral shifts. In addition. Figs. 28.2 illustrate the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO), respectively, which were the predominant contributions to the electronic transition of the PSB upon light absorption. Because the LUMO and... 

Use this expression to determine a reasonable empirical estimate of the parameter )3 for the series consisting of ethene, butadiene, hexatriene, and octatetraene given that light-induced absorptions from the HOMO to the LUMO occur at 61 500,46 080,39 750, and 32 900 cm h respectively, (b) Calculate the delocalization energy of octatetraene (see Exercise 10.36). (c) In the context of this Huckel model, the % molecular orbitals are written as linear combinations of the carbon 2p orbitals. The coefficient of the jth atomic orbital in the fcth molecular orbital is given by... 

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