M. L. Martin

Abstract The principles of the theoretical calculations of the carbon atom screening constant are reviewed. The Independent Electron, SCFMO and Valence Bond formulae are briefly discussed, and the relative importance of the different terms involved in an approximate decomposition of σ 13 C are pointed out. The variations of the excitation energy Δ E , the mean distance between the nucleus and 2p electrons, and the electronic charges and bond orders with the structure are presented. The nature of the steric effect is also explained. In a second part the various empirical correlations which make an evaluation of δ 13 C from structural and physical properties possible are shown. The actual substituent parameters of the main classes of compounds are listed and worked examples given to make the use of the tables easier. The correlations between δ 13 C and the electronic charge, electronegativity, Hammett‐Taft constants, electric field effects, geometrical parameters, spectroscopic data (electronic transitions, screening of other nuclei) and pH are also discussed with a view to appraising the carbon screening.

A theory is proposed to explain the ir spectra of highly compressed gas mixtures of the type HCl+X (or HBr, HF with X=He, Ar, Xe, N2, CO, etc.). This theory is based on the following three hypotheses: (1) The compressed mixture is formed of three molecular species, free HCl (or HBr, HF, etc.), free X, and bound van der Waals molecules (HCl···X). (2) In thermodynamic equilibrium, the system is subject to the law of mass action: HCl+X⇌(HCl···X). (3) The equilibrium constant is given by the standard formula K(T) = exp(—ΔF/RT). Using these hypotheses, the spectral perturbations are explained in terms of the calculated properties of the bound van der Waals molecules. The theory predicts that three limiting types of van der Waals molecules exist according to whether the energy of coupling between the rotation of HCl and the over-all rotation of the complex is (1) smaller than the energy of the over-all rotation of the complex [Coupling Case (1)], (2) larger than the energy of the over-all rotation of the complex but smaller than the energy of the rotation of HCl [Coupling Case (b)], (3) much larger than the energy of rotation of HCl [Coupling Case (c)]. The energy expressions are given for the three coupling cases, the equilibrium constants K (T) are calculated and the spectral perturbations are analyzed. In particular, the fine structure of the induced band is discussed.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAdvantages of nitrogen-15 NMR in studying delocalization and evaluating the energy barriers of carbon-nitrogen rotation process in amides, thioamides, and related compoundsG. J. Martin, J. P. Gouesnard, J. Dorie, C. Rabiller, and M. L. MartinCite this: J. Am. Chem. Soc. 1977, 99, 5, 1381–1384Publication Date (Print):March 1, 1977Publication History Published online1 May 2002Published inissue 1 March 1977https://pubs.acs.org/doi/10.1021/ja00447a016https://doi.org/10.1021/ja00447a016research-articleACS PublicationsRequest reuse permissionsArticle Views207Altmetric-Citations58LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts