Transition metal free reductive dimerization of nitrogen containing barbituric acid benzylidenes

Through the NMR monitoring of the reactive intermediates in the condensation of barbituric acid with nitrogen containing heterocyclic 2‐carboxaldehydes, a synthetic procedure was developed for the preparation of each of the intermediates. The simple high yield procedure for the preparation of the reductive dimer from corresponding barbituric acid benzylidenes was developed, although we were not able to elucidate the source of the reduction. The structure of the dimer was confirmed by X‐ray analysis.     

Sorption of inorganic nanoparticles in woven cellulose fabrics

Titanium dioxide was deposited from aqueous suspension onto cellulosic surfaces.Titania was sourced from Degussa (P25TM,70:30 anatase:rutile).Dry uptake of particles was shown to be rapid and dominant with one-third of the deposition occurring in less than 30 s and over one-half in the first minute.Isotherms were recorded to compare the rate of titanium deposition on dry and pre-wetted cotton.In the dry case uptake reached a maximum in 30 min whereas in the pre-wetted case the uptake was seen to continue beyond 180 min.A broad trend of higher deposition occurring at lower pH was seen,corresponding to the region where surface charges were opposite and thus attractive.Dry pickup was less significant at high pH.The response to varying ionic strength was complex and was attributed to the combined effect of charge screening,particle aggregation and consequent particle entrapment or occlusion.Titania deposition into the interstices of woven cotton sheets resulted in the formation of inorganic,nanoparticulate skeletons which could be isolated by controlled combustion of the cellulose and thus cotton was suggested to have potential for the templated synthesis of high surface area semiconductor materials.     

Density functional theory and quadratic complete basis set ab initio studies of the HNSi to HSiN isomerization and hydrogen insertion reactions with further isomerizations of the insertion products

Ab initio and density functional theory (DFT) computational studies were performed in order to determine the potential energy profiles for the inter-conversions of the small silicon–nitrogen built chemical systems: HSiN, HNSi, HSiNH₂, and HNSiH₂. Three hybrid DFT methods demonstrated high reliability in computing structures and potential energy profiles for these chemical transformations. The stability of some of these molecular systems and their interconversions was discussed and computational results were compared with experimental observations when available.     

Theoretical study of thieno[3,4-d]thiepin and furo[3,4-d]thiepin as dienes in the diels-alder reaction

Theoretical study of thiophene and furan c-fused rings with unsaturated seven membered rings with oxygen or sulfur as dienes for Diels-Alder reactions was conducted with the semiempirical Austin Model 1 (AMI). Four approaches were considered: frontier orbital theory, resonance stability of the dienophiles determined through heat of hydrogenation, progress of the reaction through bond orders, and the estimation of the reaction barriers. It was determined that the most unreactive species with the highest resonance stability are sulfur heterocyclic compounds, while furan derivatives are the most reactive. Using o-quinonoid episulfide as an intermediate was rejected because the estimated activation energy for its formation is too high. The possibility of a three bond formation in the transition state of thieno[3,4-d]thiepin reaction with ethylene was considered and rejected on the basis of AMI estimated activation energy. The S-methylated derivatives of thieno[3,4-d]thiepin were predicted to react with less reactive dienophiles like ethylene under moderate reaction conditions. If thieno[3,4-d]thiepin is not activated through S-methylation then a reactive dienophile and drastic reaction conditions are predicted to be necessary to force the cycloaddition reaction. The obtained results are in agreement with experimental evidence.     

Ab initio and density function theory computational studies of the CH4 + H → CH3 + H2 reaction

The activation barrier for the CH₄ + H → CH₃ + H₂ reaction was evaluated with traditional ab initio and Density Functional Theory (DFT) methods. None of the applied ab initio and DFT methods was able to reproduce the experimental activation barrier of 11.0-12.0 kcal/mol. All ab initio methods (HF, MP2, MP3, MP4, QCISD, QCISD(T), G1, G2, and G2MP2) overestimated the activation energy. The best results were obtained with the G2 and G2MP2 ab initio computational approaches. The zero-point corrected energy was 14.4 kcal mol⁻¹. Some of the exchange DFT methods (HFB) computed energies which were similar to the highly accurate ab initio methods, while the B3LYP hybrid DFT methods underestimated the activation barrier by 3 kcal mol⁻¹. Gradient-corrected DFT methods underestimated the barrier even more. The gradient-corrected DFT method that incorporated the PW91 correlational functional even generated a negative reaction barrier. The suitability of some computational methods for accurately predicting the potential energy surface for this hydrogen radical abstraction reaction was discussed.     

Density functional theory investigation of physical properties of the OCCN radical and the cation

Structural and thermodynamic properties for the OCCN radical and its cation were estimated with hybrid, gradient-corrected and local density functional theory methods by using three various Gaussian type basis sets. It was estimated that the radical structure should be a zig-zag structure, which corresponds to the sp² hybridization of the carbonyl carbon, while the OCCN cation is linear. The radical ionization potential should be between 8.7 and 9.1 eV with the enthalpy of formation at approximately 51 kcal/mol. It was computed in the infrared spectra that there were two strong absorptions at 1863 and 2080 cm⁻¹ for the CO and the CN functionalities and they should be observable for the OCCN radical.     

Theoretical study of structural properties, infrared spectra, and energetic properties of C4H4 isomers

A high level of ab initio and several density functional theory studies were performed with the target being to elucidate structural, spectroscopic, and energetic properties of triafulvene, cyclobutadiene, and tetrahedrane as three C₄H₄ isomers. For triafulvene all of the experimental values are available, but for cyclobutadiene only the IR spectra is known, while for tetrahedrane none of these physical values have been estimated experimentally. An excellent agreement between the computed and the experimental values were obtained where data are available, which makes it confident that the computed data should be very accurate. New structural data, IR spectra, and enthalpies of formation for both cyclobutadiene and tetrahedrane are offered.     

Barbituric acid initiated rearrangement of 2,2'-pyridil into 5,5'-(2-pyrilidine)bisbarbituric acid

[reaction: see text] In the study of the barbituric acid initiated 2,2'-pyridil rearrangement, a very efficient synthetic procedure (isolated yield 80-90%) for the preparation of useful 2-pyrilidenes 3 was developed.     

Average deviation from ideal bond order as a measure for aromaticity. AMI commuted aromatic properties of five-membered C4H4X ring systems

Average bond order deviation from that in an ideal aromatic system was proposed as a parameter for evaluation of aromaticity in general. The validity of this approach was examined by studying a series of aromatic five-membered heterocycles. The geometries and bond orders were computed with AM1 semiem-pirical method. The usefulness of AM1 semiempirical method for computation of these parameters was also discussed.