Vibrational spectra of cyclopentadienyl chlorides of titanium,zirconium and hafnium. internal rotation and thermodynamic functions

The infrared and Raman spectra of some cyclopentadienyl compounds of the transition metals, namely Ti(C₅H₅)Cl₃ and M(C₅H₅)₂Cl₂ (M = Ti, Zr and Hf), are reported and discussed. The infrared spectra of the gaseous species isolated in argon matrices at 10 K provide structural information about the single molecules. Particular attention has been paid to the low-frequency region in order to achieve more reliable assignments for the internal-rotation modes. The structural data and the fundamental frequencies derived from the spectra are employed in a calculation of the thermodynamic functions for these compounds in the ideal gas state.     

Study of the reaction of chalcone analogs of dehydroacetic acid and o-aminothiophenol: synthesis and structure of 1,5-benzothiazepines and 1,4-benzothiazines

Treatment of α,β-unsaturated carbonyl compounds, obtained by the reaction of DHA and aromatic (or heteroaromatic) aldehydes, with o-aminothiophenol results in the formation of 1,5-benzothiazepines and/or 1,4-benzothiazines depending upon the reaction conditions and structure of the aldehydes. The products were characterized by the combined use of multinuclear 1D and 2D NMR and GIAO/DFT calculations of ¹H, ¹³C and ¹⁵N chemical shifts. The tautomerism of these compounds in solution was determined, they have an exocyclic CC double bond.     

Element neighbourhoods in twofold triple systems

The method of differences is used to establish that every 2-regular multigraph onv– 10,2 (mod 3) points occurs as the neighbourhood graph of an element in a twofold triple system of orderv, with two exceptions: C₂C₃and C₃C₃.Dedicated to Professor Hanfried Lenz on the occasion of his seventieth birthday     

Pyrazoles as molecular probes to study the properties of co-crystals by solid state NMR spectroscopy

Equimolar mixtures of 3,5-dimethylpyrazole (1) with four NH-imidazoles (2–5) have been studied by¹³C and ¹⁵N CPMAS NMR and by DSC. In three cases, the solid mixture behaves as the sum of the individual components [imidazole (2), 2-methylimidazole (3) and 2,4(5)-dimethylimidazole (5)]. In one case [4,5-dimethylimidazole (4)], the mixture corresponds to a new species in which the dynamic behavior of1 no longer exists.     

Electrochemical Synthesis of MII Complexes with a Schiff Base containing an Amido Group. Crystal Structure of a Cobalt(II) Complex with a Reorganised Ligand

M(HL)(H₂O)_n complexes have been obtained by the electrochemical reaction of Fe, Co, Ni, Cu, Zn and Cd anodes with the potentially pentadentate and trianionic asymmetrical Schiff base 3‐aza‐N‐{2‐[1‐aza‐2‐(5‐nitro‐2‐hydroxylphenyl)‐vinyl]phenyl}‐4‐(5‐nitro‐2‐hydroxyphenyl)but‐3‐enamide (H₃L), containing a hard amido donor atom. The complexes have been characterized by elemental analysis, mass spectrometry, IR and ¹H NMR spectroscopies, magnetic measurements and molar conductivities. Co(HL)(H₂O) ( 2 ) has been found to rearrange in DMF solution into a crystallographically solved octahedral complex, CoL¹(H₂O)₂ ( 7 ) [where H₂L¹ is the symmetrical Schiff base ligand N,N′‐(1,2‐phenylene)‐bis(5‐nitro‐3‐hydroxysalicylidenimine)]. A hydrolysis mechanism is discussed to explain this rearrangement.     

Tautomeric conjugate acids of 2-aminopyrroles: effect of substituents, solvation and cosolute

The tautomeric preferences of the conjugated acids of 2-aminopyrrole derivatives have been examined both in the gas phase and in aqueous solution by using a combination of quantum mechanical, self-consistent reaction field and Monte Carlo–free-energy perturbation methods. The results show that the nature of substituents, the solvent and the presence of cosolute are relevant factors in modulating the relative stability between the tautomeric conjugate acids protonated at the heterocyclic ring and at the exocyclic amino nitrogen. Thus, attachment of electron-withdrawing groups to the ring, solvation in polar solvents, and the presence of negatively charged cosolutes tend to favor protonation at the exocyclic amino nitrogen. Nevertheless, none of these factors alone suffice to change the tautomeric preference for the ring-protonated forms. The results point out that the concerted occurrence of the three factors is necessary to shift the tautomeric preference towards the conjugated species protonated at the exocyclic nitrogen.Contribution to the Jacopo Tomasi Honorary Issue     

533—Structure and transport properties of artificial bipolar lipid membranes

The membranes of thermophilic archaebacteria are characterized by the presence of unusual bipolar saturated isoprenoid lipids. In order to investigate their molecular arrangement in the membrane and a possible influence on transport properties, we studied black films made from lipids of Caldariella acidophila, one of the most thermophilic archaebacteria. Details on the kinetics of formation at various temperatures are presented.Capacitance, compressibility and valinomycin-induced conductance values are compared with the corresponding data for a glycerol-monooleate (GMO) bilayer. A very peculiar behavior is presented by the bipolar lipid films studied. In fact, the values of conductance are more than two orders of magnitude lower than those of a GMO bilayer, while the values of capacitance and compressibility do not depend appreciably on the solvent in which the lipid is dispersed (in contrast with a GMO bilayer, where there is a 100% change).The results are discussed in terms of a proposed model of a monolayer organization of bipolar lipids and of the unusual composition of the hydrophobic core of the membrane.