Intra-molecular forces

Molecular Polarizability and Inter- and Intra-molecular Forces (Pitzer). ... 

G. Tammann found that potassium and sodium chlorides form a continuous series of mixed crystals between 660° and 500°. Since neither salt has a transition point, the phenomena observed when the mixed crystals are cooled must be attributed to separation of the components. With diminishing temperature, therefore, either the attractive forces within the molecules of the respective chloride must increase, or those between the unlike molecules must be greatly weakened. The results obtained by etching the individual crystals at the ordinary temperature indicate that the intra-molecular forces of the potassium chloride crystals differ from those of the sodium chloride crystal, or, more precisely, that certain lattice regions are more closely united in the former, whilst such differences are not observed in the latter. In the light of these observations, it is surprising that the X-ray analysis indicates the same lattice for each crystal. 

We now wish to extend the considerations above dealing with several different structures extending simultaneously within the same space. Thus, for example, a macromolecule attached to carbon black at one point along its length may be cross-linked to other molecules at one or more points on either or both sides of the black particle, while another may pass fairly close to the black without contacting it and be equally cross-linked at the distant points. In order to be able to develop the mathematical relationships required for the development of this theory, it is necessary to represent the state of affairs by means of a highly idealized model. However, the model proposed here is believed to contain all the elements of a uniformly filled and cross-linked elastomeric compound. The possible existence of crystallization and inter-and intra-molecular forces other than main-chain carbon to carbon links, cross links and bonds between rubber and carbon black as hypothesized earlier, is specifically neglected. 

The importance of the hydrophobic effect was for a long time underestimated. Charged interactions and hydrogen bonds are not strong intra molecular forces because water molecules compete significantly with these effects. ... 

The thermal properties of polyesters are of the greatest importance for their end applications. The important features of a polymer, such as bond strength, inter-and intra-molecular forces, resonance stability, crystallinity, structural imperfections and molecular weight, are responsible for their thermal behaviour. Long oil polyester resin and styrenated polyester resin are made flame retardant by the incorporation of bis-pyridine, bis-tribromophenoxo copper complex and polydibromophenylene oxide. 

We have seen, on the other hand, that there is a second type of internal motions particularly in very large and mobile molecules, which do not arise from the action of intra-molecular forces but which, on the contrary, are so disposed that during their execution, the potential of the molecule remains constant. These motions are caused by the thermal energy of the individual parts of the large molecule and can best be compared to the chaotic motion of the molecules in a perfect gas. It is natural, therefore, in studying this kind of internal molecular motion, to employ methods similar to those that have proved useful in the theoretical treatment of... 

I now propose a third possibility. I suggest that phosphorylation itself has a negligible direct effect on the electrical interactions of neighbouring membrane proteins, and that it is the sum of individually weak inter-molecular forces that is disrupted by phosphorylation at an allosteric site. I therefore suggest that the direct effect of phosphorylation is on intra-molecular forces in the hydrophilic domain of membrane proteins. The electrical effects of altered cation concentration may thus have served as a rather misleading model for phosphorylation effects. 

Visualising (intra)molecular force-fields and submolecular structure... 

In a rigorous formulation, the Hamiltonian of a system composed of N molecules is split into two parts as Ho(r)+ W(r). Where Hg is the reference Hamiltonian for an ideal system composed by N non-interacting molecules, but still responding to all intra molecular forces, and W is an external potential causing perturbations from the ideal behaviour. The Canonical partition function is thus written as ... 

Thus a mixture of pentane and hexane, or of ethanol and propanol, would approximate an ideal mixture, especially in the gaseous phase, where the larger distances among molecules tend to reduce the effect of the difference in inter- and intra-molecular forces. 

The variation thus of the activity coefficient with temperature depends on the excess enthalpy of mixing, which reflects the difference between inter- and intra-molecular forces. As a result, the activity coefficient of a mixture component can be a strong function of temperature as shown in Figure 13.7, the effect being determined by the other components present. This explains, for example, the large difference in the variation of y" with temperature for acetone in nCy, as compared to that in methanol. 

Furthermore, due to differences in the inter- and intra-molecular forces, the potential energy parameters X 2 = 2i, n, and 22 are different, leading to local compositions that are not the same as the overall ones. 

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