Experimental and theoretical study of the structures and enthalpies of formation of the synthetic reagents l,3-thiazolidine-2-thione and l,3-oxazolidine-2-thione

This paper reports an experimental and a theoretical study of the structures and standard (po = 0.1 MPa) molar enthalpies of formation of the synthetic reagents 1,3-thiazolidine-2-thione [CAS 96-53-7] and 1,3-oxazolidine-2-thione [CAS 5840-81-3]. The enthalpies of combustion and sublimation were measured by rotary bomb combustion calorimetry, and the Knudsen effusion technique and gas-phase enthalpies of formation values at T = 298.15 K of (97.1 ± 4.0) and −(74.4 ± 4.6) kJ·mol−1 for 1,3-thiazolidine-2-thione and 1,3-oxazolidine-2-thione, respectively, were determined. G3-calculated enthalpies of formation are in reasonable agreement with the experimental values. In the solid state, 1,3-thiazolidine-2-thione exists in two polymorphic forms (monoclinic and triclinic) and 1,3-oxazolidine-2-thione exits in the triclinic form. The isostructural nature of these compounds and comparison of their molecular and crystal structures have been analyzed. The experimental X-ray powder diffractograms have been compared with the calculated patterns from their structures for identification of the polymorphic samples used in this study. A comparison of our results with literature thermochemical and structural data for related compounds is also reported.M.T. would like to thank MEC/SEUI, FPU AP2002-0603, Spain, for financial support. A.V.D. thanks the National Science Foundation (CHE-0547566) and the American Heart Association (0855743G) for financial support of this research. The support of the Spanish Ministerio de Educación y Ciencia under Projects CTQ2007-60895/BQU and CTQ2006-10178/BQU is gratefully acknowledged

Strain Effects in Protonated Carbonyl Compounds. An Experimental and ab Initio Treatment of Acyclic Carboxamides and Ketones

Strain effects have been quantitatively evaluated for a set of 22 compounds including ketones (R2CO), carboxamides (RCONH2), and N,N-dimethylcarboxamides (RCONMe2), where R = Me, Et, i-Pr, t-Bu, 1-adamantyl (1-Ad), in their neutral and protonated forms. To this end, use was made of the gas-phase proton affinities and standard enthalpies of formation of these compounds in the gas phase, as determined by Fourier transform ion cyclotron resonance mass spectrometry (FT ICR) and thermochemical techniques, respectively. The structures of 1-AdCOMe and (1-Ad)2CO were determined by X-ray crystallography. Quantum-mechanical calculations, at levels ranging from AM1 to MP2/6-311+G(d,p)//6-31G(d), were performed on the various neutral and protonated species. Constrained space orbital variation (CSOV) calculations were carried out on selected protonated species to further assess the contributions of the various stabilizing factors. Taking neutral and protonated methyl ketones as references, we constructed isodesmic reactions that provided, seemingly for the first time, quantitative measures of strain in the protonated species. A combination of these data with the results of theoretical calculations (which also included several “computational experiments”) lead to a unified, conceptually satisfactory, quantitative description of these effects and their physical link to structural properties of the neutral and protonated species.This work was supported by grants PB 93-0289-C02 and PB-93-0142-C03-01 from the Spanish D.G.I.C.Y.T. Work by H.H. was supported by the Moroccan Ministry of Education and C.S.I.C

Experimental and Theoretical Study of the Structures and Enthalpies of Formation of the Synthetic Reagents 1,3-Thiazolidine-2-thione and 1,3-Oxazolidine-2-thione

This paper reports an experimental and a theoretical study of the structures and standard (p o ) 0.1 MPa) molar enthalpies of formation of the synthetic reagents 1,3-thiazolidine-2-thione and 1,3-oxazolidine-2-thione . The enthalpies of combustion and sublimation were measured by rotary bomb combustion calorimetry, and the Knudsen effusion technique and gas-phase enthalpies of formation values at T ) 298.15 K of (97.1 ( 4.0) and -(74.4 ( 4.6) kJ · mol -1 for 1,3-thiazolidine-2-thione and 1,3-oxazolidine-2-thione, respectively, were determined. G3-calculated enthalpies of formation are in reasonable agreement with the experimental values. In the solid state, 1,3-thiazolidine-2-thione exists in two polymorphic forms (monoclinic and triclinic) and 1,3-oxazolidine-2-thione exits in the triclinic form. The isostructural nature of these compounds and comparison of their molecular and crystal structures have been analyzed. The experimental X-ray powder diffractograms have been compared with the calculated patterns from their structures for identification of the polymorphic samples used in this study. A comparison of our results with literature thermochemical and structural data for related compounds is also reported

Supramolecular assembly of diethyl 1H-pyrazole-3,5-dicarboxylate 0.33-hydrate

In the title structure, C9H12N2O 4·0.33H2O, the molecules are present as two conformers, one of which is disordered. Another type of disorder involves N-N-H/H-N-N tautomerism. Two crystallographically independent water molecules reside on a threefold axis and some water H atoms are also disordered. Six diethyl 1H-pyrazole-3,5-dicarboxylate molecules (three pairs of conformers) and two water molecules are assembled into a supramolecular aggregate via N-H⋯N, Ow-H⋯N, Ow-H⋯Ow and N-H⋯Ow hydrogen bonds. © 2006 International Union of Crystallography. All rights reserved.Peer Reviewe

Classification of hydrogen-bond motives in crystals of NH-pyrazoles: A mixed empirical and theoretical approach

A search in the Cambridge Structural Database for NH-pyrazoles lacking other hydrogen-bond donor and acceptor sites, has identified 49 compounds that crystallize in 47 structures forming dimers (16), tetramers (13), trimers (8), hexamers (1) and catemers (10) using N-H⋯N hydrogen bonds. These structures have been classified in two classes (dimers and tetramers vs. trimers and catemers) using the accessible surface to an atom with good results. The method has been extended to new pyrazoles by means of theoretical calculations (B3LYP/6-31G*) of the geometry of the monomers. Aspects like the conformation of phenyl substituents, the additivity of substituent effects and the buttressing effect have been approached theoretically. ©ARKAT.Peer Reviewe

Weak C-H. . .O and C-H. . .N interactions in nitropyrazoles

Peer Reviewe

Supramolecular aggregation of two hydroxycarboxylic acid derivatives

4 páginas, 6 figuras, 4 tablasThe crystal structures of 7,7-dicyclobutyl-5-hydroxymethyl-6-oxabicyclo[3.2.1]octane-1-carboxylic acid, C17H26O4, (I), and 1-(hydroxymethyl)-7-oxaspiro[bicyclo[3.2.1]octane-6,1'-cyclopentane]-5-carboxylic acid, C13H20O4, (II), determined at 170 K, show that the conformation of the hydroxymethyl group (anti or gauche) affects the dimensionality (one- or two-dimensional) of the supramolecular structures via O-HO hydrogen bonds. In (I), the carboxyl and hydroxymethyl groups interact with themselves, forming a one-dimensional step-ladder, while in (II), a two-dimensional structure is made up of carboxylic acid centrosymmetric R22(8) dimers connected by hydroxyl-to-ether contacts.Peer reviewe

The unusual properties of 5-methyl-4,5,6,7-tetrahydro-1H-indazole in the solid state

The crystal structure of the title compound was determined by X-ray analysis at 200K. Three independent molecules form a trimer joined by strong and linear N- H. . . N hydrogen bonds. There is another centrosymmetrically related trimer in the unit cell. Both tautomers (1H and 2H) are present in each trimer. Disorder of the NHprotons involved in the NH . . N hydrogen bonds has been observed. Solid-state 13C CPMAS NMR was used to establish the dynamic nature of the NH-proton disorder, the title compound being the first example of proton transfer in a tautomeric mixture of pyrazoles with an equilibrium constant other than 1.The authors thank the European Community for financial support, Project No. CHRX-CT94-0582. 0.H. gratefully acknowledges a grant from the same project. We are indebted to Dr. Marfisi (Bruker Es- pabola) for the "C CPMAS NMR spectrum.Peer reviewe

Thermochemistry of organic molecules: The way to understand energy-structure relationships

14 pags, 10 figs, 4 tabsThe combination of experimental calorimetric measurements, particularly of the standard energies and enthalpies of combustion and formation, and theoretical examination of model molecules constitutes a powerful tool for the understanding of the conformational and chemical behavior of organic molecules. In this article, several examples are provided where the synergy between experiment and theory made possible the comprehension of various fundamental interactions in oxygenand sulfur-containing six-membered heterocyclic compounds, the determination of the strain energy in two C8H8 derivatives, dimethyl cubane-1,4-dicarboxylate and dimethyl cuneane- 2,6-dicarboxylate, and the calculation of the enthalpies of formation of the parent compounds, cubane and cuneane, and the study of the energy-structure relationship in barbituric acid. © 2009 IUPAC,.The support of the Spanish Ministerio de Ciencia e Innovacion under Projects CTQ2006-12745 and CTQ2007-60895/BQU is gratefully acknowledged.Peer reviewe

Thermal behavior and polymorphism in medium-high temperature range of the sulfur containing amino acids l-cysteine and l-cystine

10 pags, 11 figs, 3 tabsA thermophysical study of the sulfur containing amino acids l-cysteine and l-cystine has been carried out by differential scanning calorimetry (DSC). Heat capacities of both compounds were measured in the temperature interval from T = 268 K to near their respective melting temperatures. DSC and variable temperature powder X-ray diffraction analysis (PXRD) gave evidence for a solid–solid phase transition close to the melting point only in the l-cysteine sample. DSC experiments show that this solid–solid transition is not reversible in the temperature interval T = 235–485 K and presents a behavior depending on heating temperature, time, and rate. This behavior is also supported by variable-temperature PXRD. The patterns for the commercial samples, at room temperature, are consistent with those simulated for the orthorhombic and hexagonal polymorphic forms from the single-crystal X-ray analysis.The authors thank the support of the Spanish Ministerio de Ciencia e Innovación under Projects CTQ2007-60895/BQU, CTQ2010-16402 and HP2007-0123