Intramolecular interactions energetics

We will limit our attention to molecular energetics such as bond energies and enthalpies of formation [3] in the gas phase and bypass considerations of molecular geometries such as bond lengths and angles. The decision as to topic and to phase simplifies our understanding and aids our predictions -- we discuss only intramolecular interactions. 

Abstract The agostic bond defines an intramolecular interaction where a a bond is geometrically close to an electron deficient centre (often a transition metal). The computational studies on this energetically weak interaction are reviewed and discussed. Various types of a bonds have been considered (C-H, C-C, Si-H, Si-C, B-H). It is suggested that a C-X bond in which X carries a lone pair should preferably not be viewed as agostic. The factors that contribute to his occurrence are discussed. In particular, the agostic interaction is very sensitive to steric effects. Explanations based on molecular orbital analysis, electron delocalization and topological analysis of the electron density are presented. 

Energetic (enthalpic) interactions within bulk polymers laigely affect their end-use properties. Conformation of polymer chains is affected by intramolecular interactions. The overall strength of intermolecular interactions among particular macromolecular chains in solid state, especially in the case of ciystalline polymers and highly oriented macromolecules may be well comparable with the strength of chemical bonds. Both polymer-polymer and polymer-solvent enthalpic interactions significantly affect properties of solutions of macromolecules, which are as a rule employed for determination of their molecular characteristics. 

The nitro group, NO2, offers an array of possibilities for intramolecular interactions [46], especially when there are two or more on the same carbon. The trinitromethyl group, C(N02)3, is of particular interest as a component of energetic materials, e.g. explosives. Molecules of the type Z-C(N02)3 have been prepared and studied extensively [47] because of their potential energetic performance. A noteworthy example is [(02N)3C-CH2-0]2C=0, which has a desirably high density of 1.975 g/cm [48]. 

Theta conditions are the actual conditions under which a real polymer chain assumes its unperturbed dimensions. The solvent is then called a theta solvent and the temperature at which the unperturbed dimensions are produced is called the theta temperature. The unperturbed dimensions are realized because of the balance of two competing processes, the first being excluded volmne effects that favor open conformations and the second being unfavorable energetic contacts between the polymer and the solvent. Theta conditions mean that only short-range interactions dictate the polymer conformation because the inter- and intramolecular interactions are iden-hcal in enthalpic nature (i.e., the heat of mixing is zero). 

In general the more sterically crowded the conformation the higher its energy. Subsequent inelastic collisions will activate an energetically unstable conformation and enable the polymer to return to its original lowest energy state. The rate of internal rotation of elements of the backbone will be influenced by the magnitude of the intramolecular interactions and the efficiency of activation. The intramolecular interactions are usually of a non-bonded form and thus a function of the chemical structure of the polymer. A... 

Abstract In this chapter we analyze and systematize the data related to intramolecular hydrogen bonds and their impact on molecular geometry of nucleotides. The application of various non-empirical methods of quantum chemistry to determination of conformational characteristics of anions of the canonical 2 -deoxyribonucleotides and their methyl esters, as well as their energetics, is discussed. We revealed an existence of novel intramolecular interactions of the canonical 2 -deoxyribonucleotide anions. They are caused by incorporation of 2 -deoxyribonucleotide anions into DNA as well as by the impact of the nucleobases on the conformational features of the nucleotides and intramolecular interactions of these molecules. The efficient strategy of the evaluation of proton affinity for the different types of nucleotides is described. 

One needs, however, to ensure that the spectroscopic probe of our system provides information (in the form of spectroscopic peaks) that is energetically commensurate to the perturbations one expects to see as a result of inter- or intramolecular interactions. And here it is worthwhile to examine the energetics of... 

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