Quantum chemical study of the formation of acetylenic alcohols and 7-methylidene-6,8-dioxabicyclo[3.2.1]octanes from acetylene and carbonyl compounds

The geometric structures of the conformers of 2,3,4-trimethyl-7-methylidene-1,5-di-(thiophen-2-yl)-6,8-dioxabicyclo[3.2.1]octane were studied by the MP2/6-311++G**// B3LYP/6-31G* method. The average deviations of the calculated bond lengths from those determined by X-ray diffraction are no larger than 0.02 Å, and the deviations of the bond angles and dihedral angles are 0.7 and 3.5°, respectively. In the gas phase, the chair conformation is thermodynamically ～7.3 kcal mol^?1 more favorable than the boat conformation, and, taking into account the solvent effect of DMSO, the chair conformation is ～9.4 kcal mol^?1 more favorable. For formaldehyde and a series of ketones, including alkyl hetaryl ketones, the enthalpies of competitive formation of acetylenic alcohols and 7-methylidene-6,8-dioxabicyclo[3.2.1]octanes were calculated. The formation of the latter compounds is characterized by a considerable decrease in the enthalpy (to ?91 kcal mol^?1).     

Cyano-bridged coordination polymer nanoparticles with high nuclear relaxivity: toward new contrast agents for MRI

New water-soluble paramagnetic Gd-containing cyano-bridged metallic coordination polymer nanoparticles with a chitosan shell show high nuclear relaxivity in acidic water which is up to six times higher than that of the actually used Gd-chelates.     

Multiple bond migration with participation of a protophilic agent

The pathways of migration of the double bond in heteroallylic systems XCH₂CH=CH₂ (X =NMe₂, OMe, PMe₂, and SMe) with participation of hydroxide ion were investigated by theab initio RHF/6-31+G^* and MP2/6-31+G^* methods. The results are compared with those of analogous calculations of the systems with X=H, Me. Conformational isomerism of the initial molecules and reaction products, as well as the structure of intermediate carbanions, are considered. Increased acidity of compounds containing atoms of the third-row elements is explained in terms of a negative hyperconjugation model, 1,3-Hydrogen shift with participation of hydroxide ion in the system XCH₂CH=CH₂ results in double bond migration toward substituent X to form 1-hetero-1-propenes XCH=CHMe. Comparison of the energies of the final products indicates thermodynamic preferableness of the formation ofE-isomers. At the same time, in the case of substituents with atoms of the second-row elements the interaction of σ-bonds of the substituents and the p-AO of the terminal C atom additionally stabilizesZ-isomers of the carbanions and can be the reason for preferable kinetically controlled formation of these isomers. If the subsituents contain atoms of the third-row elements, the formation ofE-isomers of 1-hetero-1-propenes becomes both kinetically and thermodynamically predominant.