Interpretation of substituent effects on 13C and 15N NMR chemical shifts in 6-substituted purines

0369914 - ÚOCHB 2012 RIV GB eng J - Journal Article
Standara, Stanislav - Bouzková, K. - Straka, Michal - Zacharová, Z. - Hocek, Michal - Marek, J. - Marek, R.
Interpretation of substituent effects on 13C and 15N NMR chemical shifts in 6-substituted purines.
Physical Chemistry Chemical Physics. Roč. 13, č. 35 (2011), s. 15854-15864. ISSN 1463-9076. E-ISSN 1463-9084
R&D Projects: GA ČR GA203/09/2037
Grant - others:CEITEC(XE) CZ.1.05/1.1.00/02.0068; 7th European Community Framework(XE) 230955; GA MŠk(CZ) LC06030
Program: LC
Institutional research plan: CEZ:AV0Z40550506
Keywords : purine * nuclear magnetic shielding * localized molecular orbitals * conformational dependence
Subject RIV: CC - Organic Chemistry
Impact factor: 3.573, year: 2011

The present work aims to analyze the effects of substituents on the electron distribution in the purine core as reflected by NMR chemical shifts. We collected a comprehensive set of experimental NMR data for a variety of 6-substituted purines and determined the molecular and crystal structures of three derivatives by X-ray diffraction. The density-functional methods have been employed to enable understanding of the substituent-induced changes in the NMR chemical shifts of the atoms in the purine skeleton. Analyses of the nuclear shielding using localized molecular orbitals (LMOs) were used to break down the values of the isotropic 13C and 15N NMR chemical shifts and the chemical shift tensors into the contributions of the individual LMOs. The experimental and calculated trends in the chemical shift of the N-3 atom correlate nicely with the Hammett constants and the calculated natural charges on N-3, whereas the contributions of the LMOs to the N-1 and C-6 chemical shifts are found to be more complex.
Permanent Link: http://hdl.handle.net/11104/0203865