Skeletal and chlorine effects on 13C-NMR chemical shifts of chlorinated polycyclic systems

In order to establish a comparative analysis of chemical shifts caused by ring compression effects or by the presence of a chlorine atom on strained chlorinated carbons, a series of the chlorinated and dechlorinated polycyclic structures derived from "aldrin" (5) and "isodrin" (14) was studied. Compounds were classified in four different groups, according to their conformation and number of ring such as: endo-exo and endo-endo tetracyclics, pentacyclics and hexacyclics. The 13C chemical shift comparison between the chlorinated and dechlorinated compounds showed that when C-9 and C-10 are olefinic carbons, it occurs a shielding of 0.5-2.4 ppm for endo-endo tetracyclics and of 4.7-7.6 ppm for endo-exo tetracyclic. The chemical shift variation for C-11 reaches 49-53 ppm for endo-exo and endo-endo tetracyclics, 54 ppm for pentacyclic and 56-59 ppm for hexacyclic compounds. From these data, it was possible to observe the influence of ring compression on the chemical shifts

A Theoretical Investigation Of Steric Effects On 1h Chemical Shifts Of Camphor And Norcamphor Derivatives

Camphor and norcamphor derivatives provide convenient models for testing and evaluating some of the results of our work on substituted adamantanes and for checking their applicability to other systems. Our results show that the reduction in C-H bond lengths associated with steric interactions are not as pronounced in systems that are less rigid. Deshielding of 1H chemical shifts on introduction of the substituent in exo and endo positions can also be traced to angular distortions which are stronger in norcamphor, bornane and camphor than in norbornane due to additional steric interactions with a carbonyl group, with methyl groups, or with both. 1H chemical shifts are sensitive probes for steric effects, reflecting differences in bond lengths, bond angles and dihedral angles in a systematic way. Given the proper models for comparison purposes they can be used to evaluate the size of a certain group and locate its interactions with the rest of the molecular framework. © 2006 Elsevier B.V. All rights reserved.76701/03/152936Seidl, P.R., Leal, K.Z., (2001) J. Mol. Struct. (Theochem), 539, p. 159Seidl, P.R., Leal, K.Z., Yoneda, J.D., (2002) J. Phys. Org. Chem., 15, p. 801Seidl, P.R., Yoneda, J.D., Leal, K.Z., (2005) J. Phys. Org. Chem., 18, p. 162Abraham, R.J., (1999) Prog. Nucl. Magn. Reson. Spectrosc., 35, p. 85Kaiser, C.R., Basso, E.A., Rittner, R., (2001) Magn. Reson. Chem., 39, p. 643Kaiser, C.R., Rittner, R., Basso, E.A., (1994) Magn. Reson. Chem., 32, p. 503Whitesell, J.K., Minton, M.A., (1987) Stereochemical Analysis of Alicyclic Compounds by 13C NMR Spectroscopy, , Chapman & Hall, LondonDitchfield, R., (1974) Mol. Phys., 27, p. 789Abraham, R.J., Ainger, N.J., (1999) J. Chem. Soc. Perkin Trans. II, p. 441Burkert, U., Alinger, N.L., (1982) Molecular Mechanics, ACS Monograph 177, , American Chemical Society, Washington, DCAbraham, R.J., Barlow, A.P., Rowan, A.E., (1989) Magn. Reson. Chem., 27, p. 1074Carey, F.A., Sundberg, R.J., (2000) Advanced Organic Chemistry, Part A: Structure and Mechanisms. fourth ed., , Kluwer/ Plenum, New York (Chapter 3

Computational study of the effect of dispersion interactions on the thermochemistry of aggregation of fused polycyclic aromatic hydrocarbons as model asphaltene compounds in solution

Density functional theory (DFT), M\uf8ller-Plesset second-order perturbation theory (MP2), and semiempirical methods are employed for the geometry optimization and thermochemistry analysis of \u3c0-\u3c0 stacked di-, tri-, tetra-, and pentamer aggregates of the fused polycyclic aromatic hydrocarbons (PAHs) naphthalene, anthracene, phenanthrene, tetracene, pyrene, and coronene as well as benzene. These aggregates (stabilized by dispersion interactions) are highly relevant to the intermolecular aggregation of asphaltenes, major components of heavy petroleum. The strength of \u3c0-\u3c0 stacking interaction is evaluated with respect to the \u3c0-stacking distance and thermochemistry results, such as aggregation enthalpies, entropies, and Gibbs free energies (\u394G298). For both \u3c0-stacking interplanar distances and thermochemistry, the \u3c9B97X-D functional with an augmented damped R-6 dispersion correction term and MP2 are in the closest agreement with the highly accurate spin-component scaled MP2 (SCS-MP2) method that we selected as a reference. The \u394G298 values indicate that the aggregation of coronene is spontaneous at 298 K and the formation of pyrene dimers occurs spontaneously at temperature lower than 250 K. Aggregates of smaller PAHs would be stable at even lower temperature. These findings are supported by X-ray crystallographic determination results showing that among the PAHs studied only coronene forms continuous stacked aggregates in single crystals, pyrene forms dimers, and smaller PAHs do not form \u3c0-\u3c0 stacked aggregates. Thermochemistry analysis results show that PAHs containing more than four fused benzene rings would spontaneously form aggregates at 298 K. Also, round-shaped PAHs, such as phenanthrene and pyrene, form more stable aggregates than linear PAHs, such as anthracene and tetracene, due to decreased entropic penalty. These results are intended to help guide the synthesis of model asphaltene compounds for spectroscopic studies so as to help understand the aggregation behavior of heavy petroleum. \ua9 2014 American Chemical Society.Peer reviewed: YesNRC publication: Ye

The role of meetings in the social practice of strategy

This paper addresses the recent turn in strategy research to practice-based theorizing. Based on a data set of 51 meeting observations, the paper examines how strategy meetings are involved in either stabilizing existing strategic orientations or proposing variations that cumulatively generate change in strategic orientations. Eleven significant structuring characteristics of strategy meetings are identified and examined with regard to their potential for stabilizing or destabilizing existing strategic orientations. Based on a taxonomy of meeting structures, we explain three typical evolutionary paths through which variations emerge, are maintained and developed, and are selected or de-selected. The findings make four main contributions. First, they contribute to the literature on strategy-as-practice by explaining how the practice of meetings is related to consequential strategic outcomes. Second, they contribute to the literature on organizational becoming by demonstrating the role of meetings in shaping stability and change. Third, they extend and elaborate the concept of meetings as strategic episodes. Fourth, they contribute to the literature on garbage can models of strategy-making