Lead tetraacetate assisted formation of bis(acetoxy)acetic acid derivative from carvone

R-Carvone on heating with Pb(OAc)₄ in benzene gives (2RS)-2-hydroxy-2-[(1S)-4-methyl-5-oxocyclohex-3-en-1-yl)]-prop-1-yl bis(acetoxy)acetate. Alkaline hydrolysis of this compound affords the corresponding diol which under acidic catalysis is transformed into bis-hydroxy ether and 1,4-dioxane derivatives.     

An accurate analytical formula for the van der Waals potentials of homonuclear rare-gas dimers with one adjustable parameter

In the present article, the Tang–Toennies–Yiu (TTY) potential model is modified by introducing one adjustable parameter. Then, the van der Waals potentials of He₂, Ne₂, Ar₂, Kr₂, and Xe₂ are calculated by this model with the adjustable parameter being determined by the well determined well depth D_e of these systems. Based on the derived potentials, the vibrational energy spacings of these systems are also calculated. It is shown that the present derived potentials and vibrational energy spacings agree well with experiment and other theoretical calculations. Finally, the normalization constant A in the asymptotic wave function of rare-gas atoms is estimated. The present derived normalization constant A is very close to the one by calculating the ratio between the Hartree–Fock function and the asymptotic wave function. The results confirm that absorbing the first-order polarization energy into the exchange energy expression is a well approximation for the present systems.     

Conformational Panorama and Chirality Controlled Structure–Energy Relationship in a Chiral Carboxylic Acid Dimer

Chirality recognition in dimers of tetrahydro-2-furoic acid (THFA) was studied in a conformer-specific manner using rotational spectroscopy and theoretical approaches. THFA shows a strong preference for the trans- over the cis-COOH configuration. Two drastically different scenarios are possible for the detectable (THFA)₂: a kinetically preferred dimer bound by feeble interactions between two trans THFAs or a thermodynamically favored dimer with a double hydrogen-bonded ring structure between two cis subunits. To identify the conformers responsible for the extremely dense rotational spectra observed, it was essential not only to locate several hundred homo/heterochiral (THFA)₂ minima in ab initio calculations but also to evaluate the energetic connectivities among the minima. The study further reveals an interesting chirality dependent structure–energy ordering relationship. A method for enantiomeric excess (ee) determination of THFA is presented using a recently proposed chiral self-tag approach.     

Cyclophane‐Type Chlorin Dimers from Dynamic Covalent Chemistry of 2,18‐Porphyrinyl Dicyanomethyl Diradicals

2,18‐Bis(dicyanomethyl)‐substituted Ni^II porphyrin 8 and Zn^II porphyrin 11 were prepared and subjected to oxidation with PbO₂ in CH₂Cl₂ at 298 K to give cyclophane‐type chlorin dimers ( 9 )₂ and ( 12 )₂ as a consequence of double recombination of biradicals 9 and 12 , respectively. Dimer ( 9 )₂ takes a syn‐conformation of two distorted Ni^II chlorins but ( 12 )₂ takes an anti‐conformation of relatively planar Zn^II chlorins. At 298 K, dimer ( 9 )₂ is stable and its ¹H NMR spectrum is sharp but becomes broad at high temperature, while the ¹H NMR spectrum of ( 12 )₂ is considerably broad even at 298 K but becomes sharper at low temperature. These results indicate that the chlorin dimers dissociate to radical species, but the activation barrier of the dissociation of ( 12 )₂ is much less than that of ( 9 )₂. The involvement of diradicals in dynamic covalent chemistry has been suggested by thermal scrambling of hetero dimer ( 16 )₂ to give homo dimers ( 9 )₂ and ( 15 )₂.     

Synthesis of Novel Cyclodextrin Dimers Linked by Multidentate Coordination Units

Cyclodextrins(CDs)ethibitmolccularrecognitionandinclusioncatalysiswhichresemblethatofenzyInes,'buttheirbindingabilitiestoguestmoleculesareusuallyweaker.OnewayofsolvingthisproblemistointroduceanotherCDasanadditionalbindingsitetoformaCDdimer.SuperiortosingleCDderivativesinmolecularrecognitionandbindingabilitytosubstrate,theserecentlyemergingCDdimersareshowingprondseasmoresophisticatedenZymembocs.2AnumberofCDdimershavebeenpreparedtoinvestigatethebindingpropertiestoguestmolecules.However,syn…     

Dimeric Cyclodextrin Carriers with High Binding Affinity to Porphyrinoid Photosensitizers

The aim of our investigation was to develop carrier systems for an application of inert drugs in photodynamic cancer therapy. -Cyclodextrin dimers linked at their primary and secondary faces by spacers of varying lengths were synthesized as carrier systems. The binding constants of the inclusion complexes of these cyclodextrin dimers and porphyrinoid photosensitizers were determined by competitive spectrofluorometry. Particularly the secondary face linked dimers exhibited extremely high binding constants with values of 106-107 L/mol. Theoretical studies were carried out on these inclusion complexes to confirm the influence of spacer length and connecting side on complex stability.     

Geometric aspects influencing N-NTB transition - implication of intramolecular torsion

Herein we report a comprehensive study on novel carbonyl- and ethenyl-linked symmetric dimers that combine synthesis, mesomorphic properties and molecular modelling. The study has been focused on the impact of geometry imposed by the linkage group on the incidence of the twist-bend nematic (N_TB) phase. Comparison of the mesomorphic properties of these two series complemented with computational studies of conformational space around the linkage group points molecular curvature and intramolecular torsion plays important role in the appearance of the N_TB phase and can be regarded as the basic structural requirements for design of new twist-bend nematogen materials.     

新型燃速催化剂—烷基二茂铁桥联双聚分子的电化学研究

液态烷基二茂铁桥联双聚分子是一类新型燃速催化剂,它不仅具有催化活性高的优良特性,而且挥发性及迁移性均有改善,适宜用于火箭燃料复合固体推进剂。本文合成9种含不同取代基的双核二茂铁化合物,其中6种为首次合成。该9种化合物的通式为:其结构通式、各化合物的编号、英文名缩写及所含取代基和桥联基表示如下:     

Stability of (C60)2 and epoxide dimers, (C60)2ON, and their anions

The PM3, AM1, and MINDO3 semiemperical methods are used to calculate the the energy difference between C60ON and C60ON- and the bond dissociation energy necessary to cleave neutral and negatively charged (C60)2 dimers and epoxide dimers, (C60)2ON, to their respective monomers C60, and C60ON/2. The results show that the anions of the dimers are significantly more stable than neutral dimers. This result may explain the higher thermal stability of the observed ferromagnetic phase in photolyzed C60. which has been attributed to epoxide dimers and oligomers. It also provides an explanation for the origin of unpaired electron spin necessary for ferromagnetism.     

Crystal structure and magnetic properties of the coupled spin dimer compound SrCu2(TeO3)2Cl2

Single crystals of the strontium copper tellurium oxochloride SrCu₂(TeO₃)₂Cl₂ were synthesized via solid-gas reactions in sealed evacuated silica tubes. The compound crystallizes in the monoclinic system, space group P2₁, a=7.215(2), b=7.2759(15), c=8.239(2) Å, β=96.56(4)°, Z=2. The building units are [SrO₆Cl₂] irregular polyhedra, [CuO₄] and [CuO₃Cl] square planes, [TeO₃E] tetrahedra and [TeO₃₊₁E] trigonal bipyramids; E being the 5s² lone pair of Te(IV). The Cu atoms can be regarded as forming a chain of weakly connected dimers. The magnetic susceptibility of the compound shows a broad maximum typical for antiferromagnetic spin fluctuations with a non-magnetic ground state. A Heisenberg spin model with coupled s=1/2 dimers leads to a satisfactory fitting of the experimental data.