Opposed directing effect

If any change in the conditions of a system in equilibrium causes the equilibrium to be displaced, the displacement will be in such a direction as to oppose the effect of the change. 

If t he directing effects of the two groups oppose each other, the more powerful activating group has the dominant influence, but mixtures of products often result. For example, bromination of p-methylphenol yields primarily 2-bromo-4-methylphenol because —OH is a more powerful activator than -CH3. 

This is a strong directing effect that can exert stereochemical control even when steric effects are opposed. Entries 4 and 5 in Scheme 12.11 illustrate the hydroxy-directing effect. Other substituents capable of hydrogen bonding, in particular amides, also can exert a. vyn-directing effect.79... 

Example 6.2 shows that for an exothermic reaction, the equilibrium conversion decreases with increasing temperature. This is consistent with Le Chatelier s Principle. If the temperature of an exothermic reaction is decreased, the equilibrium will be displaced in a direction to oppose the effect of the change, that is, increase the conversion. 

Current density, which ranges from 2,000 to 300,000 Am 2, has been probed as an important operational variable for the sonoelectrodeposition process of massive metals [70], sonoelectrodeposition of oxide metals [80], sonoelectrosynthesis of gases [54] and also nanomaterials synthesis [96], where current density can affect crystal size in at least two opposing directions. A smaller size would be expected, on the basis of the small amount of material deposited at a lower current. On the other hand, lower current density allows more time for atomic diffusion processes to occur which can lead to larger crystal size. However, the former effect is dominant [85]. 

Compressing a gas brings the particles into close proximity, thereby increasing the probability of interparticle collisions, and magnifying the number of interactions. At this point, we need to consider two physicochemical effects that operate in opposing directions. Firstly, interparticle interactions are usually attractive, encouraging the particles to get closer, with the result that the gas has a smaller molar volume than expected. Secondly, since the particles have their own intrinsic volume, the molar volume of a gas is described not only by the separations between particles but also by the particles themselves. We need to account for these two factors when we describe the physical properties of a real gas. 

A paper published six decades ago was the first to draw attention to the possibility that a change in the rate of transport of a molecule across the plasma membrane conld play a role in regulation of both intra- and extracellnlar metabolism that is, the regulation of the blood glncose level and the intracellular metabolism of glucose. The paper was entitlied A hypothesis of insulin action is proposed which attributes to insulin the role of facilitating the rate of transport of some hexoses into the cell as opposed to a direct effect on intracellular metabolism (Levine et al. 1950). 

It is currently not known which of the many cellular consequences of exogenous DCA exposure represent primary or direct effects of DCA, as opposed to secondary, indirect phenomena. 

As opposed to the case of B, very few works investigate the direct effect of Ca on phenolic metabolism. Castaneda and Perez [131], working with lemon trees, observed that the application of 10 pM of CaCh increased PAL activity one hour earlier than control only if the trees were treated with cell walls isolated from the fungus Alternaria alternater, or... 

When the two substituents have opposed orientation effects, it is not always easy to predict what products will be obtained. For example, iV-(2-methoxy-phenyl)ethanamide has two powerful o,p-directing substituents, —OCH3 and NHCOCH3. Nitration of this compound gives mainly the 4-nitro derivative, which indicates that the—NHCOCH3 exerts a stronger influence than—OCH3 ... 

The electrons traveling on paths 1 and 2 require different times to reach III from X, due to the different distances and the opposing directions of the potential A along the paths l and /2. Here we only address the effect of the opposing directions of the potential A, namely, the distances traveled are identical over the two paths. The change in the phase difference due to the presence of the A potential is then... 

Amaral et al. [3] prepared a review providing cogent evidence that both intracellular multidrug-resistant tuberculosis (MDRTB) and intracellular methicillin-resistant Staphylococcus aureus (MRSA) can be killed by concentrations of thioridazine in the medium that is below that present in the plasma of the patients treated with this agent. Although thioridazine has been claimed to cause arrhythmias and even sudden death, the frequencies of those episodes are rare and, when present, they are related to a patient s underlying cardiac status, as opposed to the direct effect of the agent itself. 

Equation (8.55) has two variables, S and N which vary with changes in the lanthanide-ligand distance in opposing directions. However, any variations in R have led to much more pronounced changes in (5 )2 than in N. Thus the nephelauxetic effect increases when the coordination number decreases (i.e.) decrease in lanthanide-ligand distance in spite of the additive nature of ft and decrease in the number of coordinated ligands. 

If the directing effects of the groups are opposed, the more powerful activating group determines the product, although mixtures sometimes result. 

Rule [2] If the directing effects of two groups oppose each other, the more powerful activator wins out. ... 

When immersed in a magnetic field, a nueleus will experience a twisting force, or torque, which tends to line the spin axis of the nucleus up with the field, the same effect that causes two bar magnets to stick to each other in opposed directions. Because the nucleus is spinnirig, however, it will precess like a spinning top or gyroscope. 

On the other hand, when the directive effect of one group opposes that of the ler, it may be difficult to predict the major product in such cases complicated xtures of several products are often obtained. 

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