http://www.mdpi.com/journal/ijms/special_issues/nuclear-magnetic-resonance-part-2/ http://www.mdpi.com/1422-0067/4/4/231/ Ab initio calculations of the spin-spin coupling constants have been carried out for methan- and ethanimine, methanal- and ethanaloxime at the level of the second order polarization propagator approximation with coupled cluster singles and doubles amplitudes (SOPPA(CCSD)) using the aug-cc-pVTZ-J basis sets. Previously we have shown that this method can reproduce quantitatively the coupling constants for methanimine; our new results for methanal- and ethanaloxime agree also very well with the measured couplings. A study of both purely geometrical and substituent effects on all coupling constants in the title compounds is presented. Analyzing the four contributions to the coupling constants we find that the stereoelectronic effect of the nitrogen lone pair on the one-bond C-H and C-C couplings as well as the corresponding effect for the geminal N-H and N-C couplings is affected strongly by the -OH substituent. For the one-bond C-N couplings we observe that the orbital paramagnetic (OP) contribution is comparable to the Fermi Contact (FC) contribution but opposite in sign and that the spin-dipolar (SD) term amounts to between 40% and 85% of the total coupling constants. Changes in the total one-bond C-N couplings caused by the -OH substituent are also almost entirely due to SD contribution. http://www.mdpi.com/1422-0067/4/4/231/ Fri, 04 Apr 2003 00:00:00 CEST International Journal of Molecular Sciences 2003-04-04 4 4 Article 231 248 1422-0067 The Effect of Substituents on Indirect Nuclear Spin-Spin Coupling Constants: Methan- and Ethanimine, Methanal- and Ethanaloxime 2003-04-04 doi: 10.3390/i4040231 Patricio F. Provasi Gustavo A. Aucar Stephan P. A. Sauer http://www.mdpi.com/1422-0067/4/4/218/ Some calculations of the electric field derivative of the spin-spin coupling constant on molecules in the series CH3F, CH3Cl, CH3Br, CH3I, CH4, CH3Li, CH3Na and CH3K have been presented. The data is broken down into the 4 terms of the Ramsey theory: Fermi contact (FC); diamagnetic spin-orbit (DSO); paramagnetic spinorbit (PSO) and spin-dipolar (SD). The FC term is seen to dominate all the calculated Js and their derivatives presented here. The situation where the FC term does not dominate in other molecules is discussed as a contrast. http://www.mdpi.com/1422-0067/4/4/218/ Fri, 04 Apr 2003 00:00:00 CEST International Journal of Molecular Sciences 2003-04-04 4 4 Article 218 230 1422-0067 Electric Field Effects on 2JHH Spin-Spin Coupling Constants 2003-04-04 doi: 10.3390/i4040218 Martin Grayson http://www.mdpi.com/1422-0067/4/4/203/ Correlation effects on the change of 1J(CH) couplings in model systems I:NCH...H2O and II:CH4...H2O as a function of the H...O distance are discussed. RPA and SOPPA results follow a similar trend in system II. In system I RPA values decrease monotonously as the H...O distance decreases, while SOPPA ones exhibit flat maximum near equilibrium. Such different behavior is ascribed to the π-transmitted component. Intermolecular couplings at the equilibrium geometry of I are analyzed by means of the CLOPPA approach. The larger absolute value of 2hJ(CO) compared to 1hJ(HO) is found to arise from contributions involving a vacant LMO localized in the C-H...O moiety. http://www.mdpi.com/1422-0067/4/4/203/ Fri, 04 Apr 2003 00:00:00 CEST International Journal of Molecular Sciences 2003-04-04 4 4 Article 203 217 1422-0067 Electronic Mechanisms of Intra and Intermolecular J Couplings in Systems with C-H···O Interactions 2003-04-04 doi: 10.3390/i4040203 Claudia G. Giribet Martin C. Ruiz de Azua Celia V. Vizioli Claudio N. Cavasotto http://www.mdpi.com/1422-0067/4/4/193/ coming soon http://www.mdpi.com/1422-0067/4/4/193/ Fri, 04 Apr 2003 00:00:00 CEST International Journal of Molecular Sciences 2003-04-04 4 4 Article 193 202 1422-0067 Through-Space Spin-Spin Coupling In Acetylenic Systems. Ab Initio and DFT Calculations 2003-04-04 doi: 10.3390/i4040193 Alessandro Bagno Girolamo Casella Giacomo Saielli Gianfranco Scorrano http://www.mdpi.com/1422-0067/4/4/158/ coming soon http://www.mdpi.com/1422-0067/4/4/158/ Fri, 04 Apr 2003 00:00:00 CEST International Journal of Molecular Sciences 2003-04-04 4 4 Article 158 192 1422-0067 Extension of the Karplus Relationship for NMR Spin-Spin Coupling Constants to Nonplanar Ring Systems: Pseudorotation of Tetrahydrofuran 2003-04-04 doi: 10.3390/i4040158 Anan Wu Dieter Cremer