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Structural and Electronic Properties of Chiral Molecules on Surfaces
Get PDFFrancesco Antonio Gianturc
4-Methoxybenzamidinium hydrogen sulfate
No full textThe title salt, C8H11N2O +·HSO4 -, has been synthesized by the reaction between 4-methoxybenzamidine and sulfuric acid. The asymmetric unit comprises a nonplanar 4-methoxybenzamidinium cation and one hydrogen sulfate anion. In the cation, the amidinium group has two identical C-N bonds [1.306(2) and 1.308(2)Å], and its plane forms a dihedral angle of 6.49(8)°with the mean plane of the benzene ring. The ionic components are associated in the crystal via N-H+⋯O-, resulting in chains running approximately along the b-axis direction whicg are interconnected by O-H⋯O- hydrogen bonds
"Studio teorico della stabilità relativa dei cristalli di s-cis e s-trans 5-formiluracile"
No full textFirst X-ray diffraction and quantum chemical study of proton-acceptor and proton-donor forms of 5-carboxylcytosine, the last-discovered nucleobase
No full textThe recently-discovered nucleobase 5-carboxylcytosine (caC) is the final product of oxidative attack on the 5 position of cytosine. It can exist in solution in an equilibrium of different protonated and unprotonated forms within a range of pH, although only the zwitterionic caC(+/-) and the anionic caC(-) species have been detected in the liquid phase. In this work, four proton-transfer compounds of caC have been prepared by varying chemical reagents to ensure different pH during crystallization, and then determined by X-ray crystallography: 5-carboxylcytosinium chloride, bromide and nitrate and 5-carboxylcytosinate phenylbiguanidium. Both cationic and anionic species of caC exist in the solid state as canonical aminooxo tautomers. In caCH(+)-containing compounds, site protonation always occurs at N3 imino atom. Structural changes in the heterocyclic ring of cationic and anionic forms of caC can be interpreted, in terms of valence bond theory, as an increase in the contribution of different polar canonical forms. Quantum chemical calculations on unionized 5-carboxylcytosine, as well as on the zwitterionic and the anionic species, are also reported in order to estimate the relative energies of the possible tautomeric forms. Theoretical calculations confirm the existence in the isolated molecules of the strong intramolecular hydrogen bond found in the crystal between the adjacent amino and carboxyl groups. (C) 2013 Elsevier B.V. All rights reserved
"Molecular modelling of 5-formyluracil crystal tautomers by Carr-Parrinello and Force Field methods"
No full text4-Methoxybenzamidinium chloride monohydrate
No full textIn the cation of the title compound, C8H11N 2O+·Cl-·H2O, the C-N bonds of the amidinium group are identical within experiemental error [1.305(2) and 1.304(2)Å], and its plane forms a dihedral angle of 25.83(8)° with the phenyl ring. The ionic components are associated in the crystal into polymeric hydrogen-bonded supramolecular tapes stabilized by N-H +⋯Cl- and N-H+⋯Ow intermolecular hydrogen bonds, and by Ow-H⋯Cl- interactions
Supramolecular association in proton-transfer adducts containing benzamidinium cations. II. Concomitant polymorphs of the molecular salt of 2,6-dimethoxybenzoic acid with benzamidine
No full textTwo concomitant polymorphs of the molecular salt formed by 2,6-dimethoxybenzoic acid, C9H10O4 (Dmb), with benzamidine, C7H8N2 (benzenecarboximidamide, Benzam) from water solution have been identified. Benzamidinidium 2,6-dimethoxybenzoate, C7H9N2+center dot C9H9O4- (BenzamH(+)center dot Dmb(-)), was obtained through protonation at the imino N atom of Benzam as a result of proton transfer from the acidic hydroxy group of Dmb. In the monoclinic polymorph, (I) (space group P2(1)/n), the asymmetric unit consists of two Dmb(-) anions and two monoprotonated BenzamH(+) cations. In the orthorhombic polymorph, (II) (space group P2(1)2(1)2(1)), one Dmb(-) anion and one BenzamH(+) cation constitute the asymmetric unit. In both polymorphic salts, the amidinium fragments and carboxylate groups are completely delocalized. This delocalization favours the aggregation of the molecular components of these acid-base complexes into nonplanar dimers with an R-2(2)(8) graph-set motif via N+-H center dot center dot center dot O- charge-assisted hydrogen bonding. Both the monoclinic and orthorhombic forms exhibit one-dimensional isostructurality, as the crystal structures feature identical hydrogen-bonding motifs consisting of dimers and catemers
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