Dependence on conformation

Another interesting question concerns the rate at which each tosylate undergoes elimination. A tosylate sample contains molecules with several different conformations. The size of each conformer population depends on conformer energy, and the more reactive tosylate will probably be the one with the largest population of reactive conformers, i.e., molecules whose geometries allow anti elimination. Which tosylate, cis or trans, will have a larger population of reactive conformers Explain how you reached this conclusion. 

The extent of ion binding depends on a number of characteristics of the polyion degree of dissodation, acid strength, conformation, distribution of ionizable groups and cooperative action between these groups (Wilson Crisp, 1977 Oosawa, 1971 Harris Rice, 1954, 1957). The hydration state of the macromolecule, which is in turn dependent on conformation, also affects ion binding (Begala, 1971). 

The conformation of macro- or polyions has been defined and discussed briefly in Section 4.1.1. The conformation of a polyion is determined by a balance between contractile forces, which depend on conformation free energy, and extension forces, which arise from electrical free energy. The extent of conformational change is determined by several factors. Changes are facilitated by the degree of flexibility of the polyion, and conformational change is greatest at low concentration of polyions. 

The critical adsorption energy. A critical adsorption energy is predicted by many theories (2-6). Its value is dependent on conformational properties of the polymer and usually estimated as a few tenths ofkT (7). Yet, a method to determine x c experimentally has never been suggested. Displacement studies provide such a method. Inspection of Equation 5 bears out that Xsc is obtained from a displacement isotherm, provided that Xgd and the solvency terms vanish. This condition is met by taking as the displacer a molecule which is (nearly) identical to the repeating unit of the polymer, i.e. the polymer is displaced by its own monomer. Such... 

The properties such as b.p., m.p., v.p., etc., are dependent on the size and shape of macromolecules and also on the interaction between individual segments of molecules. They are also found to depend on conformations of macromolecules and thus on the structure of molecules. 

The photochemistry of conjugated polyenes has played a central role in the development of modern molecular photochemistry, due in no small part to its ultimate relevance to the electronic excited state properties of vitamins A and D and the visual pigments, as well as to pericyclic reaction theory. The field is enormous, tremendously diverse, and still very active from both experimental and theoretical perspectives. It is also remarkably complex, primarily because file absorption spectra and excited state behavior of polyene systems are strongly dependent on conformation about the formal single bonds in the polyene chain, which has the main effect of turning on or off various pericyclic reactions whose efficiencies are most strongly affected by conformational factors. 

Molecular mechanics calculations on two 6-arylpyrrolo[2,l-d][l,5]benzothia-zepines (1995JMC4730) confirmed that binding to a mitochondrial benzodiazepine receptor depends on conformational strain as well as on specific repulsive interactions involving their side-chains. 

It must be independent of rigid translation and (proper) rotation of the given atomic coordinates, although it may depend on conformation. 

The first term on the right hand side gives the intramolecular contribution in the laboratory system which depends on conformation and orientation of the relevant single segments that means it depends on the mean intramolecular structure. The second term requires knowledge about the intermolecular structure within the monodomains. 

An enzyme that is involved in the biosynthesis of carrageenan has been detected in seaweed extracts.387 It converts 6-O-sulfo-D-galactosyl into 3,6-anhydro-D-galactosyl units at the polymer level, and this structural change significantly affects gelling properties that depend on conformation.384... 

To keep the review within reasonable limits, the aromaticity of expanded porphyrins will be discussed only very briefly, mostly to provide examples of certain phenomena. The aromatic properties of expanded porphyrins often depend on conformational effects, and the amount of available data places these interesting molecules outside the scope of the present review. Furthermore, only all-carbon linked systems will be discussed, and nitrogen bridged systems, such as phthalocyanines will not be included. 

Also in 2-substituted ethanesulphonates,35 the 33S chemical shift has a reverse substituent effect and correlates with both Taft substituent constants and the chemical shift of the carboxylic carbon in related carboxylic acids. It seems that the substituent effect does not depend on conformation, but prevailingly on intramolecular electronic effects. Density functional theory (DFT) calculations of 33S nuclear shielding constants and natural bond orbital (NBO) analysis made it possible to conclude that substituents cause a variation in the polarization of the S-C and S-O bonds and of the oxygen lone pairs of the C — S03 moiety. This affects the electron density in the surroundings of the sulphur nucleus and consequently the expansion or contraction of 3p sulphur orbitals. 

Note that there are other types of protons not listed here that can fall into the same chemical shift ranges listed above. The above categories are simply the most common ones. Also, through-space ( anisotropic ) effects of unsaturated groups (C=C, 0=0, and aromatic rings) can change chemical shifts from the above categories in ways that depend on conformation. 

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