Bonding slate molecular

For example, as shown by calicheamicin, cyclic enediynes have a lower activation barrier than acyclic enediynes. As suggested by Nicolaou in 1988, the distance between the acetylenic carbons that form the covalent bond influences the rate of cyclization. Another theory developed by Magnus and Snyder is based on the molecular strain between ground state and transition slate this seems to be more general, especially for strained cyclic systems. Often, as both the distance and the strain are not known, the development of suitable precursors remains difficult, as exemplified by the following enediyne, in which a slight change leads to a cycloaromatization ... 

The six tt molecular orbitals of 1,3,S-hexaCriene. in the ground slate, only the three bonding MO s are occupied. In the excited stale, ili.i and [Pg.1257]

The traditional S 2 reaction is a concerted process, as illustrated in eq. (2.8). The electron pair of Nu hinds to the carbon at which displacement is occurring. simultaneously with the departure ol 1. . along with the electron pair ol the C — I, bond. In the transition slate for the reaction, iwo lobes ol an orbital of approximately p hybridization on (he central carbon overlap with orbitals of Nu and I. , respectively. A molecular orbital scheme would assign the iwo electron pairs noted above io the two lowest molecular orbitals (A and ID o the linear ihrce-center subsystem. Trout this picture, the observed inversion of configuration follows. Most commonly die... 

Electric quadrupole interaction between electric quadrupole moment of the nucleus and electric field gradient at the nuclear site Quadrupole splitting A q a. Molecular symmetry b. Oxidation slate (nominal valency) c. Spin Slate d. Bonding properties... 

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