Dimers modes

Loll, P.J. etal.,Aligand-mediated dimerization mode for vancomycin, Chem. Biol, 5, 293,1998. 

Comparison with Buzanowski s Figure 5 using chain transfer to Mayo dimer mode)... 

Although virtually of no synthetic significance, the dimerization of carbonyl ylides is capable of providing O-bridged compounds. It is noteworthy that both head-to-tail 726 (88TL317) and head-to-head 727 (86BCJ255) dimerization modes can be in effect here. 

If the proton oscillations are not coupled to the dimer oscillations, the dynamics can be modeled by symmetric and antisymmetric normal coordinates for proton modes (xa,xs) and for dimer modes (Xa,Xs). Then the total wave function is... 

In the case when the proton and dimer modes are coupled, the normal coordinates become linear combinations of the proton and dimer s atoms coordinates. Fermions and bosons are not distinguished, and we have a conflict with the Pauli principle The two protons are not distinguished in the ground state. 

For intermediate systems, such as the HF dimer, mode specificity can be attributed to the differences in bonding of the two hydrogens.85 Likewise, in the NO dimer the two neighboring states with drastically different lifetimes correspond to two types of stretch vibrations. In the larger systems, however, such direct identification of the regular states is not always possible. Moreover, it is clear83,86 that the slowly decaying states are superimposed on other states with much faster decay, a behavior that can be anticipated theoretically. 

The RRKM rate for dimer dissociation must be treated with some care. For instance, it is not clear whether the van der Waals modes (six in the case of aniline—CH4) are more strongly coupled to the dissociation continuum than they are to the aniline or the CH4 modes. Kelley and Bernstein (1986) assume that the coupling between van der Waals modes and the rest of the dimer modes is weak so that the RRKM calculation includes only van der Waals modes. If on the other hand, the rest of the modes are coupled to the van der Waals modes, then all of them must be included in the RRKM density and sums of states calculations. In some cases it will make little difference which mechanism is assumed because the dissociation limit is often below an energy at which the molecular modes will contribute much density. In the case of aniline, only a few modes are below the dimer binding energy so that they contribute very little to the density of states. 

Biosynthetically, 125 is considered to be a dimer of 127, which itself could be an oxidation product of 126. The manner in which two avrainvillamide units are linked strongly indicates a dimerization mode that has not yet been described for indole alkaloids. Initiation of the dimerization by a hetero-Michael addition reaction sets the stage for the synthesis of 125. Until now, three syntheses of stephacidin B (all based on the dimerization of avrainvillamide) have been accomplished, by Myers et al. [55], Baran et al. [57, 58], and Williams et al. [59]. 

Four related Pd-catalyzed linear dimerization modes have been observed for the intermole-cular reaction of 1,3-dienes (Scheme 2). While potentially of industrial importance for bulk... 

Recent advances in each of the four Pd-catalyzed linear diene dimerization modes (Scheme 2 dimerization without trapping dimerization with incorporation of protic H—Y trapping reagents dimerization with incorporation of silanes or disilanes and... 

The second term in the enthalpy expression is the zero-point vibrational energy contribution. In the formation of a complex from two nonlinear molecules, three degrees of rotational and three degress of translational freedom are lost. These appear as low-frequency vibrational modes ( dimer modes ) in the complex. A hydrogen-bonded complex may have as many as six more vibrational modes than the sum of the modes in the monomers, and AE usually has a destabilizing effect. The second vibrational term, A AEy) is the change in the thermal... 

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