Y-coupling

Fig. 20. The sigma lone pair group MO s of X4 component system and the sigma group MO s of the Y-Y coupling unit...

Translation to lattice energy transfer is the dominant aspect of atomic and molecular adsorption, scattering and desorption from surfaces. Dissipation of incident translational energy (principally into the lattice) allows adsorption, i.e., bond formation with the surface, and thermal excitation from the lattice to the translational coordiantes causes desorption and diffusion i.e., bond breaking with the surface. This is also the key ingredient in trapping, the first step in precursor-mediated dissociation of molecules at surfaces. For direct molecular dissociation processes, the implications of Z,X,Y [Pg.158]

For centrosymmetric complexes the intensities of the parity-forbidden d< d bands arise through vibronic interactions and consequently show substantial temperature dependence. It can be shown that for the ideal case of a si ngle harmonic vibration of frequency y coupled to the electronic system the intensity of a band should be given by105-106... 

To dramatize the possible similarity of the responses for E compared to EC,E mechanisms, our calculations employed similar E° values for the A/B and X/ Y couples. This is not, however, an unusual situation for electrode products, considering that many may be closely related in structure to the reactant (e.g., as isomers). Obviously, the CV result of Figure 23.1 alone does not provide sufficient information to prove the cathodic fate of A. 

Attack opposite 05" would allow immediate departure of 05" without pseudorotation or protonation of X or Y. Protonation or juxtaposed charges could facilitate attack by making P more positive and thus reduce the energy of the activated complex. Either would also likely stabilize the pentacovalent intermediate ES and might trap it for a finite time. Witzel (519) has emphasized both of these points without reference to pseudorotation. Protonation of X or Y coupled with pseudorotation could allow 03 to leave forming the 2, 5"-diester, but such isomerization does not occur. 

Pan et al. reported similar reactions of / -quinones to 4-allyl-4-hydroxycyclohexa-2,5-dienone derivatives (Equation (26)).194 Unsymmetrical quinones show high selectivity in the addition of allylindium reagents to the carbonyl group. Indium-mediated allylation of 1,2-diones occurs via a y-coupling fashion to yield ct-hydroxy keto compounds. In some cases of cinnamylation, the corresponding a-coupling products are obtained (Equation (27)).195,196... 

To avoid isolating the glycal, the reaction was quenched with an excess of borane in THF and, upon oxidative work-up under basic conditions, C-disaccharide 38 was obtained in 64% yield over two steps (Scheme 11) (77). The stereochemistry of the hydroboration step was verified on the corresponding acetate by examination of the Jy%T and J2 y coupling constants in the proton NMR spectra. 

Shinbo T, Sugiura M, Kamo N, and Kobatake Y. Coupling between a redox reaction and ion transport in an artificial membrane system. 

Arii, T. Kishi, A. Kobayashi, Y. Coupled DSC and x-ray diffraction instrument. TTiennochim. Acta 1999, 325, 151-156, Rigaku Application Note Presented at the 48th Annual Denver X-ray Conference, 1999. 

---