Cs configuration

In the gas phase, the halogen azides have a trans Cs-configuration like HN3 with an N-N-N bond angle around jy JO 127,143 -jjjg lengths are significantly different. 

The cs-configuration of the C-3 hydrogen of cinchonamine (145) was assigned by Wenkert and Bringi 44) who converted dihydro-cinchonamine (143) and dihydrocorynantheol (165), which has an a-hydrogen at C-3, into the same quaternary tosylate 166. This assign-... 

In MO theory, the network of chemical bonds is determined by the occupied MO in the system ground state. For reasons of simplicity, assume the closed-shell (cs) configuration of N = 2n electrons in the standard spin-restricted HF (RHF) description, which involves the n lowest (doubly occupied, orthonormal) MO. In the familiar LCAO MO approach, they are expanded as linear combinations (LC) of the (Lbwdin) orthogonalized AO x = iXoXi - -XJ = iXi) contributed by the system constituent atoms (x x)= 8, si, = ( 2,... ) = J = xC, where the rectangular matrix C = = (x ) groups the relevant expansion coefficients of MO (i.e., LC... 

The LE biexciton states are shown in Figure 6.22 right panel, black lines. By having CS configurations, there are an additional 75 biexciton states, making a total of 90 biexciton states. In this case, we also follow the conventional labeling of states, that is, Fx , where F is the total angular momentum and x = A,B,C,... for CS biexciton states cs is added between Fand x. 

In the present calculations, the molecule is restricted to Cs symmetry. There are five internal degrees of freedom fthe out-of-plane mode is excluded to preserve C, symmetry). Nuclear configurations will be denoted R = (R(H -O). / (0-H ), / (h2-H ), corresponding to the... 

Fig. 10. Conformational flooding accelerates conformational transitions and makes them accessible for MD simulations. Top left snapshots of the protein backbone of BPTI during a 500 ps-MD simulation. Bottom left a projection of the conformational coordinates contributing most to the atomic motions shows that, on that MD time scale, the system remains in its initial configuration (CS 1). Top right Conformational flooding forces the system into new conformations after crossing high energy barriers (CS 2, CS 3,. . . ). Bottom right The projection visualizes the new conformations they remain stable, even when the applied flooding potentials (dashed contour lines) is switched off.

The structures observed in the mass spectra of fullerene molecules covered with alkaline earth metals, as described in the previous section, all seem to have a geometric origin, resulting in particularly stable cluster configurations every time a highly symmetrical layer of metal atoms around a central fullerene molecule was completed. When replacing the alkaline earth metals by an alkali metal (i.e., Li, Na, K, Rb, or Cs), a quite different situation arises. 

The chemical reactions through cyclic transition states are controlled by the symmetry of the frontier orbitals [11]. At the symmetrical (Cs) six-membered ring transition state of Diels-Alder reaction between butadiene and ethylene, the HOMO of butadiene and the LUMO of ethylene (Scheme 18) are antisymmetric with respect to the reflection in the mirror plane (Scheme 24). The symmetry allows the frontier orbitals to have the same signs of the overlap integrals between the p-or-bital components at both reaction sites. The simultaneous interactions at the both sites promotes the frontier orbital interaction more than the interaction at one site of an acyclic transition state. This is also the case with interaction between the HOMO of ethylene and the LUMO of butadiene. The Diels-Alder reactions occur through the cyclic transition states in a concerted and stereospecific manner with retention of configuration of the reactants. 

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