Steric aspects

Steric aspects of the formation of metal chelate complexes. V. G. Dashevskii, A. P. Baranov and M. I. Kabachnik, Russ. Chem. Rev. (Engl Transl), 1983, 52,152-167 (105). 

The preponderance of stereochemical data in the literature has been obtained from studies using 2-pentene, which now appears to have been a rather poor substrate for emphasizing steric aspects of the reaction. Recent experiments utilizing 4-methyl-2-pentene (76) have given much clearer indications of steric control in metathesis reactions (vide infra). 

The rate of reaction in collision theories is related to the number of successful collisions. A successful reactive encounter depends on maw things, including (1) the speed at which the molecules approach each other (relative translational energy), (2) how close they are to a head-on collision (measured by a miss distance or impact parameter, b, Figure 6.10), (3) the internal energy states of each reactant (vibrational (v), rotational (/)), (4) the timing (phase) of the vibrations and rotations as the reactants approach, and (5) orientation (or steric aspects) of the molecules (the H atom to be abstracted in reaction 634 must be pointing toward the radical center). 

Indeed, considering the latter 3D QSAR model, the features that make a molecule suitable to bind to the hERG channel start delineating in a chemically interpretable manner, but, it is rather dear how these kinds of models emphasize mostly the 3D steric aspects of molecules, depending mainly on factors such as the conformation (or the conformational analysis protocol) or the alignment of the molecules. To obtain a description of the characteristics of hERG-blocking molecules in terms of measurable (computable) properties in a way that the physicochemical determinants of the activity can be identified, the classical 2D QSAR approach is well suited. 

It would be expedient to widen synthetic applications of distonic ion-radicals. In principle, they allow developing dual reactivity—at the sites of radical unsaturation and, separately, of charge localization. The sterical aspects of ion-radical organic chemistry can also be estimated as intriguing, but they are insufficiently developed. The so-called confined ion-radical organic chemistry promises serious perspectives, too. 

Note that in Eq. 11-3, in contrast to the equation used for describing bulk phase partitioning, CA, is not the total surface area (TSA,) of the organic molecule. Rather it reflects the contact area between the molecule and the surface. But as a first approximation, we will assume that CA, is proportional to TSA,. By doing so, we neglect any special steric aspects that may affect the ability of a sorbate to closely approach the surface moieties with which it interacts. 

Steric aspects of the stereoselectivity of enol ketonisation were extensively examined by Zimmerman and coworkers from 1955 to 1959 (the main results... 

Which catalyst should be chosen for a given reaction will depend upon chemical, steric, and mechanistic factors. The application of Pearson s soft and hard acid-base (SHAB) principle has often proved a valuable qualitative guide as to suitable surface sites for a particular reactant. In fact, certain solids actually owe their catalytic power to attached Bronsted or Lewis acid and base groups as exemplified by weak acid ion exchange resins (Sect. 2.3), alumina (Sect. 3.2), and sometimes charcoals. Steric aspects can be con-... 

Steric Aspects. We owe much of our knowledge of cis-trans isomerism in carotenoids to the studies of Zechmeister. ... 

Pitt, G. A. J., and R. A. Morton, Steric Aspects of the Chemistry and Biochemistry of Natural Products, Cambridge University Press, Cambridge, 1960, p. 67. 

O. Tapia, H. Eklund, and C.I. Branden, "Molecular, Electronic, and Structural Aspects of the Catalytic Mechanism of Alcohol Dehydrogenase, in Steric Aspects of Biomolecular Interactions, G. Ndray-Szabd and K. Simon (Eds.), CRC Press, West Palm Beach, 1987. 

Table 1 Steric aspects of drug action (Continued)...

Tapia, O., Eklund, H., and Branden, C.I. (1987) in Naray-Szabo, G. and Simon, K. (eds.) Steric Aspects of Biomolecular Interactions, CRC Press, Boca Raton, p. 159. 

Steric aspects The fluorine atom is considerably smaller than the rest of the halogen atoms. Seen from the steric point of view it resembles more hydrogen than chlorine (Table 15.17). Effectively fluoro-derivatives differ from the other halogenated derivatives because fluorine forms with carbon particularly stable bonds and, in contrast to other halogens, is only rarely ionized or displaced. Because it is both chemically inert and of small size organic fluorine is often compared to hydrogen. 

Patil, P. N., LaPidus, J. B., Campbell, D., Tye, A. Steric aspects of adrenergic drugs. II. Effects of DL isomers and deoxy derivatives on the reserpine-pretreated vas deferens. J. Pharmacol. Exp. Then 1967, 155, 13-23. 

A recent series of pharmacological studies has analyzed certain steric aspects of adrenergic drug structures ... 

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