Finite temperature vibronic spectra of harmonic surfaces: a time-dependent coupled cluster approach

An algorithm to compute vibronic spectra of harmonic surfaces including Dushinsky rotation and Hertzberg–Teller terms is described. The method, inspired by thermo field dynamics, maps the thermal density matrix onto the vacuum state and uses the time-dependent coupled cluster ansatz to propagate it in time. In the Franck–Condon approximation where the dipole matrix elements are taken to be constants, this reduces to the auto correlation function of the new vacuum. In the Hertzberg–Teller approximation, the full time evolution operator is needed. This too is governed by a closed set of equations. The theoretical development is presented along with an application to anthracene.     

Three structures of dispirooxindole derivatives generated in situ through a three‐component one‐pot strategy with complete regio‐ and stereoselectivity

The challenging molecular architecture of spirooxindoles is appealing to chemists because it evokes novel synthetic strategies that address configurational demands and provides platforms for further reaction development. The [3+2] cycloaddition of the carbonyl ylide with arylideneoxindole via a five‐membered cyclic transition state gave a novel class of dispirooxindole derivatives, namely tert‐butyl 4′‐(4‐bromophenyl)‐1′′‐methyl‐2,2′′‐dioxo‐5′‐phenyl‐4′,5′‐dihydrodispiro[indoline‐3,2′‐furan‐3′,3′′‐indoline]‐1‐carboxylate, C₃₆H₃₁BrN₂O, (Ia), 5′‐(4‐bromophenyl)‐1,1′′‐dimethyl‐4′‐phenyl‐4′,5′‐dihydrodispiro[indoline‐3,2′‐furan‐3′,3′′‐indoline]‐2,2′′‐dione, C₃₂H₂₅BrN₂O₃, (Ib), and tert‐butyl 1′′‐methyl‐2,2′′‐dioxo‐4′‐phenyl‐5′‐(p‐tolyl)‐4′,5′‐dihydrodispiro[indoline‐3,2′‐furan‐3′,3′′‐indoline]‐1‐carboxylate, C₃₇H₃₄N₂O₅, (Ic). Crystal structure analyses of these dispirooxindoles revealed the formation of two diastereoisomers selectively and confirmed their relative stereochemistry (SSSR and RRRS). In all three structures, intramolecular C—H...O and π–π interactions between oxindole and dihydrofuran rings are the key factors governing the regio‐ and stereoselectivity, and in the absence of conventional hydrogen bonds, their crystal packings are strengthened by intermolecular C—H...π interactions.     

The Zolmitriptan-Pyridine (1:1) and Zolmitriptan-Propiophenone (3:2) Inclusion Complex

Abstract  

The crystal structures of zolmitriptan with pyridine (I) and propiophenone (II) solvates have been determined by single crystal X-ray diffraction studies. Compound (I) crystallizes in the orthorhombic space group P2₁2₁2₁ with a = 8.5610(5) ?, b = 12.2709(7) ?, c = 19.6201(12) ?, V = 2061.1(2) ?³, and Z = 4, while compound (II) crystallizes in the monoclinic space group P2₁ with a = 15.085(1) ?, b = 19.656(12) ?, c = 21.0860(13) ?, β = 92.068(1)°, V = 6248(4) ?³ and Z = 4. The asymmetric unit of (I), C₁₆H₂₁N₃O₂·C₅H₅N, contains one zolmitriptan molecule and one pyridine solvate, while the asymmetric unit of (II), 3(C₁₆H₂₁N₃O₂)·2(C₉H₁₀O) comprises six zolmitriptan molecules and four propiophenone solvates. In both structures, the N–H···N hydrogen bonds, form an infinite helical chain and generate a C(11)-type motif in (I) and a D₂²(13)-type motif in (II). Both the complexes have layer structures, the layers being constructed from rings (cavity) of four zolmitriptan molecules, hydrogen bonded through N–H···N and N–H···O bonds, where the pyridine (I) and propiophenone (II) solvates are included in an R₄⁴(33) ring.     

Preparation and characterization of polypropylene and waste tire powder modified by allylamine blends

Waste tire powder subjected to allylamine modification in the presence of ultraviolet (UV) radiation has been used to prepare polypropylene based thermoplastic vulcanizates with maleic anhydride polypropylene (MA‐PP) as compatibilizer. The effect of increasing the concentration of MA‐PP on performance characteristics like tensile strength, elongation and rheological properties have been investigated. X‐ray diffraction studies of the PP/waste tire powder blend indicate the disappearance of β crystalline peaks on addition of waste tire powder in the PP, whereas it is observed in the allylamine modified rubber powder loaded PP. Differential scanning calorimetry results further supported the above fact. The improvement in mechanical properties of the PP/allylamine modified rubber powder loaded thermoplastic vulcanizates has been explained in terms of βα transformation of PP crystals during straining of the samples and uniform dispersion of allylamine coated rubber powder in the PP matrix. The melt rheological properties of the thermoplastic vulcanizates loaded with modified rubber powder are higher than its counterpart due to the higher dispersion as a result of chemical interaction between the rubber powder surface with the MA‐PP. Copyright © 2008 John Wiley & Sons, Ltd.     

Oppolzer sultam directed aldol as a key step for the stereoselective syntheses of antitumor antibiotic belactosin C and its synthetic congeners

[reaction: see text] An efficient protocol has been developed using D-(2R)-Oppolzer sultam as a chiral auxiliary for generating anti/syn diastereomers with high enantiopurity and utilized in the efficient synthesis of natural product belactosin C and their synthetic congeners. It has been observed that a variation in the stoichiometry of the Lewis acid led to a difference in anti/syn selectivity.     

Bulk-wave and guided-wave photoacoustic evaluation of the mechanical properties of aluminum/silicon nitride double-layer thin films

The development of devices made of micro- and nano-structured thin film materials has resulted in the need for advanced measurement techniques to characterize their mechanical properties. Photoacoustic techniques, which use pulsed laser irradiation to nondestructively induce very high frequency ultrasound in a test object via rapid thermal expansion, are suitable for nondestructive and non-contact evaluation of thin films. In this paper, we compare two photoacoustic techniques to characterize the mechanical parameters of edge-supported aluminum and silicon nitride double-layer thin films. The elastic properties and residual stresses in such films affect their mechanical performance. In a first set of experiments, a femtosecond transient pump–probe technique is used to investigate the Young’s moduli of the aluminum and silicon nitride layers by launching ultra-high frequency bulk acoustic waves in the films. The measured transient signals are compared with simulated transient thermoelastic signals in multi-layer structures, and the elastic moduli are determined. Independent pump–probe tests on silicon substrate-supported region and unsupported region are in good agreement. In a second set of experiments, dispersion curves of the A₀ mode of the Lamb waves that propagate along the unsupported films are measured using a broadband photoacoustic guided-wave method. The residual stresses and flexural rigidities for the same set of double-layer membranes are determined from these dispersion curves. Comparisons of the results obtained by the two photoacoustic techniques are made and discussed.     

Doppler-free/Doppler-sliced ion imaging

We demonstrate a hybrid Doppler-free/Doppler-sliced ion imaging approach that is well-suited for detection of H or D atoms. The method relies on 2 + 1 resonant ionization with identical, nearly counterpropagating beams that are coplanar but directed at a small angle relative to the detector face. This results in Doppler selection of the velocity component along the time of flight axis but Doppler-free detection in the plane perpendicular to this axis. The results show high signal level and excellent slicing ( approximately 5%), yielding velocity resolution completely determined by cation recoil in the ionization step.     

Ti(III)-mediated radical cyclization of β-aminoacrylate containing epoxy alcohol moieties: synthesis of highly substituted azacycles

Ti(III)-mediated radical cyclization of β-aminoacrylate containing 2,3-epoxy alcohol moieties led to the formation of highly substituted piperidine and pyrrolidine rings. The pyrrolidine ring system was then transformed into an indolizidine framework present in many natural products.     

Coenzyme B12 model studies: An HSAB approach to the equilibria and kinetics of axial ligation of alkyl(aquo)-cobaloximes by imidazole and cyanide

Kinetics and equilibria of the axial ligation of alkyl(aquo)cobaloximes by imidazole and cyanide have been measured spectrophotometrically in aqueous solutions of ionic strength 1.0 M at 25°C as a function of pH. Comparison of K_IMD and K_CN- of CH₃, C₂H₅ and BrCH₂cobaloximes indicates that their stability is in the order BrCH₂>CH₃>C₂H₂. As the electron-withdrawing capacity of the alkyl grouptrans to water increases, the electron density of the cobalt(III) decreases and thus it becomes a stronger Lewis acid and binds more strongly to imidazole and cyanide. The association and dissociation rate constants are better correlated to the relative softness of the ligand showing that cyanide binds 30 times faster than imidazole. These complexes are isolated and are characterized by IR and¹H NMR spectra.     

Stereoselective synthesis of (+)-cryptocarya diacetate by an iterative Prins cyclisation and reductive cleavage sequence

A highly stereoselective synthesis of (+)-cryptocarya diacetate is achieved through our recently developed strategy for the construction of 1,3-diols via Prins cyclisation. The route relies mainly on the reductive cleavage of allylic ethers, ozonolysis and Wittig olefination along with Prins cyclisation.