Intramolecular effects

In addition to the intramolecular effects, steric factors are of considerable influence. The most usual one consists of steric hindrance to attack on the lactam nitrogen atom. Certain examples of this will be given. By comparison with uracil, it would be expected that uric acid (10) would be iV-methylated in the pyrimidine ring, but that in the imidazole ring 0-methylation should also be possible. However, the experiments of Biltz and Max show that all uric acid derivatives which carry a hydrogen atom in the 9-position are converted by ethereal diazomethane into l,3,7-trimethyl-8-methoxyxanthine (11). The following are examples uric acid and its 1-methyl, 3-methyl, 7-methyl, 1,3-dimethyl, 1,7-dimethyI, 3,7-dimethyl, and 1,3,7-trimethyl derivatives. Uric acid derivatives which arc substituted by alkyl groups in the 3- and 9-positions (e.g., 3,9-dimethyl-, 1,3,9-trimethyl-, and 3,7,9-trimethyl-uric acid)do not react at all with diazomethane, possibly because of insufficient acidity. Uric acids which are alkylated... 

As shown in Fig. 1.3, MIFs account not only for intramolecular effects, but also for intermolecular interactions, allowing macroscopic properhes to emerge. The interactions of a chemical with a solvent reveal such pharmacologically essen-hal properties as solubility (Chapters 10 and 11) and partihoning/lipophilicity (Chapters 12-16). The interactions between a large number of idenhcal molecules... 

Caron, G., Reymond, F., Carrupt, P. A., Girault, H. H., Testa, B. Combined molecular lipophilidty descriptors and their role in understanding intramolecular effects. Pharm. Sci. Technol. Today 1999, 2, 327-335. 

Mayer, J.M., Testa, B van de Waterbeemd, H., and Bornand-Crausaz, A. Non-additivity and intramolecular effects in the partition coefficient of omega-functionalized alkylpyridines, Eur. J. Med. Chem., 17(5) 453-459, 1982. 

One of the methods of following changes in intermolecular and intramolecular effects is to heat the sample and compare the changes in the spectra as the sample is... 

The effect is observed when the heavy atom is substituted in the molecule (intramolecular effect) as also when the molecule collides with a heavy atom containing perturber (intermolecular or external effect). The dramatic enhancement of S —T transition due to intramolecular and intermolecular heavy atom perturbations are respectively shown in Figure 3.8 for chloronaphthalenes in ethyl iodide and other perturbants. Molecular oxygen has a perturbing effect on S — T absorption spectra of organic molecules in solution. Under a pressure of 100 atm of Os, well defined... 

Is there a universal stabilization mechanism valid for the complete range of systems from simple atoms to complex molecules or are intramolecular effects more dominant in some cases than others ... 

Lord, R. C., and F. A. Miller Factors influencing vibrational frequencies of molecules intramolecular effects. Appl. Spectroscopy 10,. 115—123 (1956). 

Nonlinear optical (NLO) properties are usually considered to depend on the intrinsic features of the molecule and on the arrangement of a material. An intermediate level of complexity should also be taken into account, that of the formation of well-defined supermolecules, resulting from the association of two or more complementary components held together by a specific array of intermolecular interactions (1). Such intermolecular bonding may yield more or less pronounced NLO effects in a variety of supramolecular species (2). Thus, three levels of nonlinear optical properties may be distinguished the molecule, the supermolecule and the material. The molecular and supramolecular levels involve respectively - intramolecular effects and structures, -... 

The intermolecular shielding surface and the effects of electric fields on shielding (shielding polarizabilities and hyperpolarizabilities) are useful in the interpretation of long-range intramolecular effects and in intermolecular effects on shielding. 

Figure 3.86 Ag+ tunnelling in a 1,3-alternate calixarene. This fast intramolecular effect is distin guishable from intermolecular processes by IINMRspectroscopy.

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