Resonance assisted

The theory of resonance-assisted coupling of H-bonding and torsions... 

According to (5.101) the rotation barrier varies linearly with the shift in resonance weights (or bond orders) on going from one resonance form to the other. Thus, resonance hybrids with particular sensitivity to intermolecular interactions (such as resonance-assisted H-bonds, Section 5.2.3) can be expected to exhibit strong... 

Figure 5.65 provides theoretical evidence that resonance-assisted H-bonding can serve as an effective mechanism for switching a methyl rotor from one preferred conformation to another, or for controlling the stiffness of torsional motions in alkylated amides. In particular, the torsional potentials of proteins (more specifically, the Ramachandran b angle at Ca) should be sensitive to N—H- O and related H-bonding interactions involving the amide backbone. In principle, this electronic... 

The quantity 2 was defined as the difference in bond length of the two C—C bonds in the ring. This value varied from 6 pm up to 106 pm. Since and 2 linearly were related, as might be expected, the values of their sum, Q, was useful in discussing resonance-assisted hydrogen bonding. The value of Q was found to correlate well with " th other properties. 

There has been nothing like the enthusiasm for the application to these systems of the theoretical equations, which we have noted in the previous sections and will encounter in the next. Nevertheless, a number of features are present which are qualitatively consistent with the discussions in Sec. 5.8.1 and which are in part illustrated in Table 5.11. There is a correlation of rate constant with the driving force of the internal electron transfer. -pjjg p. itro-phenyl derivative is a poorer reducing agent when protonated and k is much less than for the unprotonated derivative. Consequently disproportionation (2A 3) becomes important. Although there are not marked effects of structural variation on the values of A , the associated activation parameters may differ enormously and this is ascribed to the operation of different mechanisms."" The resonance-assisted through-chain operates with the p-... 

Steiner, Th. (1998a). Structural evidence for resonance-assisted 0-H...S hydrogen bonding. Chem. Comm. 411-2. 

The pKa for dissociation of its proton is 12.3 and the hydrogen-bonded proton is probably located in the center of the bond with both amino groups sharing the charge.160 Enols can also form unusually strong "resonance-assisted" hydrogen bonds ... 

The relationship between tautomerism and aromaticity is strong both in carbocyclic chemistry (e.g., phenol) [37, 38] and in heterocyclic chemistry (e.g., 2-hydroxypy-ridine) [39, 40], We consider that the cycle should be formed by covalent bonds, thus excluding the possibility that rings comprising hydrogen bonds, the so-called resonance assisted hydrogen bonds (RAHB), could be aromatic [41 45],... 

A typical example of a resonance assisted device might be a cell separator designed to discriminate between cells which have only a small difference in dielectric properties. The cross over frequencies from positive to negative DEP will be similar but not identical for the two cells. By working at a frequency between the two crossovers it is possible to separate the cells but the forces produced will be small unless very high fields are used (Fig. 10). Controlled resonance can be used to boost the fields at the working frequency. 

The superparamagnetic resonance, assisted by computer simulations, provides a new method of morphological analysis of magnetic nanoparticles. 

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