10.1021/jo200954c.s003 Brendan Kelly Brendan Kelly Daniel H. O'Donovan Daniel H. O'Donovan John O'Brien John O'Brien Thomas McCabe Thomas McCabe Fernando Blanco Fernando Blanco Isabel Rozas Isabel Rozas Pyridin-2-yl Guanidine Derivatives: Conformational Control Induced by Intramolecular Hydrogen-Bonding Interactions American Chemical Society 2016 series dihedral angle intramolecular interactions 1 H NMR spectra NMR analysis guanidinium salts pyridine N 1 atom derivative guanidinium protons B 3LYP guanidine data Conformational Control Induced pyridine ring 2016-02-22 14:27:25 Dataset https://acs.figshare.com/articles/dataset/Pyridin_2_yl_Guanidine_Derivatives_Conformational_Control_Induced_by_Intramolecular_Hydrogen_Bonding_Interactions/2581933 The synthesis and conformational analysis of a series of pyridin-2-yl guanidine derivatives using NMR, X-ray crystallography, and B3LYP/6-31+G** theoretical studies are reported. A remarkable difference was observed in the <sup>1</sup>H NMR spectra of the guanidinium salts as compared with their <i>N</i>,<i>N</i>′-di-Boc protected and neutral analogues. This difference corresponds to a 180° change in the dihedral angle between the guanidine/ium moiety and the pyridine ring in the salts as compared to the Boc-protected derivatives, a conclusion that was supported by theoretical studies, X-ray data, and NMR analysis. Moreover, our data sustain the existence of two intramolecular hydrogen-bonding systems: (i) between the pyridine N1 atom and the guanidinium protons in the salts and (ii) within the <i>tert</i>-butyl carbamate groups of the Boc-protected derivatives. To verify that the observed conformational control arises from these intramolecular interactions, a new series of <i>N</i>-Boc-<i>N</i>′-propyl-substituted pyridin-2-yl guanidines were also prepared and studied.