Destabilizing effect

Thioesters Like chlorine sulfur is a third row element with limited ability to donate a pair of 3p electrons into the carbonyl tt system With an electronegativ ity that IS much less than Cl or O however its destabilizing effect on the carbonyl group IS slight and thioesters he m the middle of the group of carboxylic acid derivatives m respect to reactivity... 

Stability. AH calcitic and dolomitic limestones are extremely stable compounds, decomposing only in fairly concentrated strong acids or at calcining temperatures of 898°C for high calcium and about 725°C for dolomitic stones at 101.3 kPa (1 atm). A very mild destabilizing effect is caused by C02-saturated water, as described in the preceding section on solubihty. Aragonite, however, is not as stable as calcite. In sustained contact with moisture,... 

Quicklime and hydrated lime are reasonably stable compounds but not nearly as stable as their limestone antecedents. Chemically, quicklime is stable at any temperature, but it is extremely vulnerable to moisture. Even moisture in the air produces a destabilizing effect by air-slaking it into a hydrate. As a result, an active high calcium quicklime is a strong desiccant (qv). Probably hydrate is more stable than quicklime. Certainly hydrated lime is less perishable chemically because water does not alter its chemical composition. However, its strong affinity for carbon dioxide causes recarbonation. Dolomitic quicklime is less sensitive to slaking than high calcium quicklime, and dead-burned forms are completely stable under moisture-saturated conditions. 

High initial cost and environmental restrictions prevent use of oil and synthetic muds in many cases where shale problems are expected. It is necessary then to treat a water-base mud to minimize the destabilizing effect of the drilling fluid. Salts, polymers, and other organic materials are added to the mud to reduce the water sensitivity of the shale, shale sweUing, and weakening arising from mud contact, or the rate of water uptake by the shale. 

The presence of polysulfonates in petroleum sulfonates used in lube formulations has a destabilizing effect on the formulation stabiUty and function of the sulfonate in motor oils, etc. Special techniques are utilized to help reduce the carryover of residual sludge components, including the use of hydrocarbon solvents such as hexane or heptane to faciUtate separation of sludge, often with centrihigation. Other desludging procedures include water wash, H2SO4 wash, clay percolation, and filtration. 

This is opposite from the order in solution as revealed by the pK data in water and DMSO shown in Table 4.14. These changes in relative acidity can again be traced to solvation effects. In the gas phase, any substituent effect can be analyzed directly in terms of its stabilizing or destabilizing effect on the anion. Replacement of hydrogen by alkyl substituents normally increases electron density at the site of substitution, but this effect cannot be the dominant one, because it would lead to an ordering of gas-phase acidity opposite to that observed. The dominant effect is believed to be polarizability. The methyl... 

The effect of substituents has been probed by MO calculations at the STO-3G level. An isodesmic reaction corresponding to transfer of a proton from a substituted <7-complex to an unsubstituted one will indicate the stabilizing or destabilizing effect of the substituent. The results are given in Table 10.1. 

The Baeyer strain theory is useful to us in identifying angle strain as a destabilizing effect. Its fundfflnental flaw is its assumption that the rings of cycloalkanes are planar-. With the exception of cyclopropane, cycloalkanes are nonplanar. Sections 3.5-3.13 describe the shapes of cycloalkanes. We ll begin with cyclopropane. 

Saturated hydrocarbons show a slight stabilizing effect on the initial state but a very destabilizing effect on the transition state, consistent with arguments based on solvent polarity. 

Jamieson and McNeill [142] studied the degradation of poIy(vinyI acetate) and poly(vinyI chloride) and compared it with the degradation of PVC/PVAc blend. For the unmixed situation, hydrogen chloride evolution from PVC started at a lower temperature and a faster rate than acetic acid from PVAc. For the blend, acetic acid production began concurrently with dehydrochlorination. But the dehydrochlorination rate maximum occurred earlier than in the previous case indicating that both polymers were destabilized. This is a direct proof of the intermolecular nature of the destabilizing effect of acetate groups on chlorine atoms in PVC. The effects observed by Jamieson and McNeill were explained in terms of acid catalysis. Hydrochloric acid produced in the PVC phase diffused into the PVAc phase to catalyze the loss of acetic acid and vice-versa. 

Based on experimental results and complementary calculations, an out-of-plane n-delocalization is suggested for thiirene dioxides39. As far as the thiirene oxide is concerned, theoretical calculations predict possible spiroconjugative-type53 interaction between the n c—c orbital of the ring and the jr-orbitals of the SO (which leads to aromatic stabilization and a n charge transfer backward from the SO to the C=C). There exists, however, a rather strong destabilization effect, due to the jr so(d )-orbital. 

In all of the above, the activating, directive and stabilizing destabilizing effects are similar in principle to those in the acyclic systems. However, the magnitude of these effects per se, or in conjunction with other characteristics of the systems in point, are considerably different and, consequently, the ultimate chemical results may be different. 

FIGURE 6.3. The strain hypothesis for the catalytic reaction of lysozyme. The enzyme is assumed to destabilize the chair geometry by pushing the ground state substrate toward the sofa configuration. This ground-state destabilization effect is supposed to reduce Ag M. 

The contribution of Co A is presumably limited to 35 % by the destabilizing effects of absence of a metallic orbital and decreased d character of the bond orbitals, which oppose the stabilizing effect of the quartet atomic state. In the same way nickel involves resonance between the two following structures, in the ratio 30 70 (saturation moment 0-61) ... 

The destabilizing effect of the adjacent charge rule shown in covalent nitrates does not occur in the analogous compounds containing carbon as the central atom, such as carbonates, urea, guanidine, etc., since the quadricovalent carbon atom is neutral. 

The pressure waves when reflected from the top wall interact with the flame again and cause a destabilizing effect on the flame front. The flame is accelerated toward a denser medium and the growth of the perturbations thus turbulizes the flame front via Rayleigh-Markstein instability mechanism. 

Important literature is available for this type of ylides which are usually thermally stable in the case of phosphorus, arsenic or stilbene C-substituents. This is different for ylides C-substituted by nitrogen atoms which have a destabilizing effect. 

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