Conformations and reactivity

The competition between these two reactions is determined by the effect of substituents on the conformation and reactivity of the diradical intermediate. 

Analysing structure, conformation and reactivity means that the mol-... 

M. M. Bhadbhade, and D. Srinivas, Effects on molecular association, chelate conformation and reactivity toward substitution in Cu(5-X-salen) complexes, salen = N,N -ethylenebis (salicyli-denaminato), X = H, CH3O and Cl synthesis, X-ray structures and ERR investigations, Inorg. Chem. 32, 5458-5466 (1993). 

Reductive decyanations of 2-cyanotetrahydropyran derivatives with sodium in ammonia yield predominantly axially protonated products. The observations are consistent with the reductive decyanation proceeding via the pyramidal, axial radical which accepts a second electron to give a configurationally stable carbanion, which in turn abstracts a proton from ammonia with retention of configuration (Rych-novsky, S. D. Powers, J. P. LePage, T. J., J. Am. Chem. Soc., 1992, 114, 8375-8384). Provide an explanation for the axial preference of the intermediate free radical on the basis of orbital interactions. Hint The title of the paper by Rychnovsky et al. is Conformation and Reactivity of Anomeric Radicals. ... 

A. M. Brouwer, J. Cornelisse, and H. J. C. Jacobs, /. Photochem. Photobiol. A Chem., 42, 313 (1988). Photochemistry of 2,5-Dimethyl and 2,5-di-tert-Butyl-l,3,5-hexatrienes— Conformation and Reactivity—A Quantitative Study. 

The stereochemistry at two of the stereogenic centres of chlorocarolide was unknown when this structure was published—stereochemistry is one of the hardest aspects of structure to determine. Nonetheless, NMR is second only to X-ray in what it tells us of stereochemistry, and we shall look at what coupling constants (/ values) reveal about configuration, conformation, and reactivity. The first aspect we consider is the determination of conformation in six-membered rings. 

Studies in the held of tin-substituted cycloalkanes stem in part from a desire to understand the modifications, in terms of conformation and reactivity, brought to the carbacycle by the inclusion of increasing numbers of heteroatoms. Although not strictly heterocycles, cyclic polystannanes allow this line of investigation to be taken to its extreme conclusion, and as such they are included in this article for comparison. The synthetic routes to cyclostannanes are summarized in Eqs. (19)-(23), with details in Table I (91-103). 

There may be two reasons for the reported evidence of dijferences in conformation and reactivity in aqueous solution (1) substantial differ-... 

Hon, F. H., and Tidwell, T. T., Steric crowding in organic chemistry. III. Spectral properties, conformations, and reactivities of highly substituted ferrocenylcarbinols, J. Org. Chem. 37, 1782-1786(1972). 

Serianni AS (2000) Carbohydrate Structure, Conformation, and Reactivity NMR Studies with Stable Isotopes. In Hecht SM (ed) Bior-ganic Chemistry Carbohydrates. Oxford University Press, New York, p 244... 

A review of the genus Berberis lists the alkaloids obtained and includes discussion of the chemistry of some recently isolated alkaloids and the pharmacology of berbamine and the crude extracts of Berberis species.The chemistry, biochemistry, and pharmacology of curare have also been reviewed. Other alkaloids whose pharmacology has been discussed are AN -dimethylberbamine and related alkaloids,trilobine and isotrilobine, and isotetrandrine and tetrandrine. The conformation and reactivity of the last alkaloid has been discussed in the light of an X-ray study. A method for quantitative extraction of tubocurarine from biological materials has been described. ... 

In accordance with this view, the present article aims to first present protein adsorption and its ramifications, such as the effects of adsorption on conformation and reactivity, from a fundamental physicochemical approach insofar as present knowledge allows. Mention is made of features relevant to biological systems at appropriate points. Following this, some of the many areas where interface studies of proteins are pertinent to important problems in biology are discussed. 

Abstract This chapter emphasises on the important aspects of steric and stereo-electronic effects and their control on the conformational and reactivity profiles. The conformational effects in ethane, butane, cyclohexane, variously substituted cyclohexanes, and cis- and tra/ ,v-decalin systems allow a thorough understanding. Application of these effects to E2 and ElcB reactions followed by anomeric effect and mutarotation is discussed. The conformational effects in acetal-forming processes and their reactivity profile, carbonyl oxygen exchange in esters, and hydrolysis of orthoesters have been discussed. The application of anomeric effect in 1,4-elimination reactions, including the preservation of the geometry of the newly created double bond, is elaborated. Finally, a brief discussion on the conformational profile of thioacetals and azaacetals is presented. 

Abstract The A(1,2) and A(1,3) strains and their control on the conformational and reactivity profiles of substrates are discussed. The application of A(1,3) strain to the facial selectivity of reactions such as [2,3] and [3,3] sigmatropic shifts, intramolecular SN2 reactions, hydroboration, enolate alkylation, etc. is highlighted. The high diastereoselectivity observed in the reactions of enolates derived from 4-substituted /V-al kanoyl-1,3-oxazolidinones (Evans enolates) with electrophiles is discussed. 

The most important structural features that influence the conformation and reactivity of cycloalkanes differ depending on whether small (cyclopropane and cyclobutane), common (cyclopentane, cyclohexane, and cycloheptane), medium (cyclooctane through cycloundecane), or large (cyclododecane and up) rings are... 

With some cyclic ketones, the a-cleavage can also be followed by intramolecular hydrogen abstraction that eventually leads to an unsaturated ring-opened aldehyde. An alternative reaction path involves formation of a ketene. The competition between these two reactions is determined by the effect of substituents on the conformation and reactivity of the diradical intermediate. ... 

Thermochemical data, and in particular the enthalpies of formation of oxygen-and sulfur-containing six-membered heterocycles, provide essential information on the factors responsible for the contrasting behaviour (structural, conformational and reactivity) between these types of compounds. Understanding of the experimental thermochemical observations has required theoretical modeling to confirm the relative importance of the steric, electronic, electrostatic and stereo-electronic interactions that are responsible for the enthalpies of formation for 1,3- and 1,4- dioxanes, 1,3,5-trioxane and their... 

The difference in energy values of the complexes with (R)-alanine and (S)-alanine is due to the optimized conformation of the initial protein conformation. Molecular interaction energy values favor complex formation with (R)-alanine. That is, the feasibility of mutants can be analyzed from their conformation and reactivity. However, mutants for chromatographic separation should be prepared with co-enzyme or a co-en me-like compound to maintain their stereostructure. The structure of homo DAO is shown in Figure 10.6. The optimized structure is veiy similar to the ICOP M215R mutant shown in Figure 10.5. 

Bent bonds are also known as banana bonds or t (tau) bonds. For a discussion of the utility of this model in explaining molecular conformation and reactivity, see Wintner, C. E. /. Chem. Educ. 1987, 64, 587 and references therein. 

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