Interactions, destabilizing

The anomalous iodoacetamide-fluoride reaction violates this rule, in that a less stable -halonium complex (18) must be involved, which then opens to (19) in the Markownikoff sense. This has been rationalized in the following way estimates of nonbonded destabilizing interactions in the possible products suggest that the actual product (16) is more stable than the alternative 6)5-fluoro-5a-iodo compound, so the reaction may be subject to a measure of thermodynamic control in the final attack of fluoride ion on the iodonium intermediate. To permit this, the a- and -iodonium complexes would have to exist in equilibrium with the original olefin, product formation being determined by a relatively high rate of attack upon the minor proportion of the less stable )9-iodonium ion. 

Display electrostatic potential maps for both anti and gauche conformers of 1,2-ethanediol. Do you see any examples of destabilizing interactions (between like charges) or stabilizing interactions (between unlike charges) in either conformer Are you able to explain the observed conformational preference ... 

Again, one may take the difference of the enthalpies of hydrogenation of the diene and the sum of those for the two monoenes. Doing this separately for 14 and 15, we find the reaction enthalpies for the Z- and -dienes are —1.9 1.2 and —1.8 1.1 kJmol-1. These values are effectively zero. A stabilizing—or destabilizing—interaction was not expected for nonconjugated acyclic dienes and none was found. 

Figure 3.58 The mnemonic energy-level-splitting diagram for the four-electron destabilizing interaction of two occupied non-orthogonal orbitals.

It is clear that when overlap is neglected the four electron destabilizing interaction becomes zero, i.e. AE = 0. 

We now focus on the four electron destabilizing interactions. A comparison of the destabilizing interaction w—0j and is very simple. The destabilizing... 

On the other hand, the four electron destabilizing interaction, <(>i —i, is larger for cis union than trans because the overlap integral is larger in the former case. 

However, the two electron stabilizing interaction dominates the four electron destabilizing interaction. Thus, cis union will be more favorable than trans union. In other words, here we have an application of the regiochemical rule stating that the union of two open shell fragments having a total of 4N + 2 pi-electrons will be predisposed to be cis. 

In other papers408, the discussion of conjugative destabilization has been based on an incorrect assumption, L e that the destabilizing interaction of filled orbitals increases as their energy separation decreases, while, as we have seen in Eq. (5 ), four electron overlap repulsions depend not on the energy separation of the two interacting MO s but rather on the sum of them. Thus, situation A is less destabilizing than situation B (constant Sy). 

When discussing the relative weights of the various types of interactions, simultaneously and not independently at work in a stable solid, it should be kept in mind that stabilizing interactions can be effective even in the presence of repulsive forces, as well as the opposite, namely destabilizing interactions may be observed in the presence of attractive forces. An appreciation of this conceptual distinction is crucial to the understanding of the effect of ionic charges on the nature of pair-wise non-covalent interactions. Particularly when the ions carry the same charge. 

The findings discussed above led Herbrandson and Cusano to the conclusion that the thermodynamically less stable diastereomer (-)-62 has the (i5)-configuration because in this structure there is a strong destabilizing interaction between the aromatic ring and the isopropyl group of the menthyl residue. X-Ray analysis of (->62 confirmed the correctness of this assignment (204). 

Unusual M-H H-M interaction is rationalized in the following terms The weak H H contact is a four-electron destabilizing interaction between the a M-H bonding levels, where mixing of the a M-H levels produces a weakly bonding character. 

Figure 1.9 Stabilizing and destabilizing interactions of CF3 anion and CF2 carbene.

O—C destabilizing interactions. Scaling the 1,4-interactions to 70% of full value correctly identifies the equilibrium ratio of this system. 

In 3-formylpyridine a different orientation is imposed (79JCR(S)46) on the carbonyl group by the OMe and SMe substituents in the 2-position the former imparts stabilization to the N,0-frans and the latter stabilization to the N,0-cis conformations. Electrostatic stabilizing and destabilizing interactions should involve the pair of atoms 0,S and 0,0, respectively. 

Filled orbitals which cannot physically separate because they are part of the same molecule may have substantially larger overlap than the intermolecular case, and the destabilizing interaction, , may be much larger than the stabilizing interaction, AeL-The net repulsion will lead to conformational changes so as to minimize the repulsive interactions. If the interaction cannot be avoided by conformational change, then as the result of the interaction, a pair of electrons is raised in energy. The system has a lower... 

Non-planarity is the result of the dominance of the destabilizing interactions of the sulfur lone pair and tt- occupied MOs of the pentadienyl anion over the stabilizing interaction of that lone pair and the LUMO of the anion fragment. In fact thiabenzene is antiaromatic in a planar configuration. Pyramidalization reduces the antiaromaticity induced by the sulfur. Although no X-ray data are available on the parent system, kinetic data have been obtained supporting a minimum barrier to inversion at the pyramidal sulfur of a 2-thianaphthalene of 99.1 kJ mol-1 (75JA2718). The formulation of the system as a cyclic ylide is supported by the chemical reactivity of the compounds as related in the reactivity section below. 

---