bluuebunny/crossref_metadata_2025 huggingface dataset:
Light-hole and heavy-hole transitions for high-temperature long-wavelength infrared detection
Authors: Lao Y. F. , Pitigala P. K. D. D. P. , Perera A. G. U. , Liu H. C. , Buchanan M. , Wasilewski Z. R. , Choi K. K. , Wijewarnasuriya P.
Published: September 2010

Hole transitions from the heavy-hole (hh) to the light-hole (lh) band contributing to the 4–10 μm response range are reported on p-GaAs/AlGaAs detectors. The detectors show a spectral response up to 16.5 μm, operating up to a temperature of 330 K where the lh-hh response is superimposed on the free-carrier response. Two characteristic peaks observed between 5–7 μm are in good agreement with corresponding energy separations of the lh and hh bands and thus originated from lh-hh transitions. Results will be useful for designing multi-spectral detection which could be realized on a single p-GaAs structure.
Further Studies of Depolarization Ratios in the Raman Spectrum of Aqueous Formate Ion
Authors: Spinner E
Published: September 2010

Raman spectral depolarization ratios (ρ = IX(ZY)Z/IX(YY)Z) have been determined for solutions of H12C16O2Na, D12C16O2Na, H13C16O2Na, and H13C18O2Na in D2O. The maximum value of ρ, 3/4, required for all vibrations in which some molecular symmetry is lost, is observed throughout only for the out-of-plane bending band. For CH in-plane bending ρ, in solution in D2O, ranges from 0.55 for H12C16O2- to 0.62 for H13C18O2-; for H12C16O2- in H2O p is lower still, viz. 0.48. For the carboxylate stretching band in the region 1593 cm-1 to 1533 cm-1 ρ is in the range 0.50 to 0.58. For an HCO2- ion of C2v symmetry both these vibrations are of species b1, i.e., non-totall
symmetric. The fact that ρ for both is well below 0.75 shows that the formate ion in water actually has no plane of symmetry perpendicular to the ionic plane. Coriolis interaction between CH in-plane bending and the nearby (second) carboxylate stretching motion is not a major cause of the low ρ for the former; the principal interaction involved is one between two
vibrations of identical symmetry species, which for H12C16O2- are close to accidental resonance. For CD in-plane bending in DCO2- ρ is much higher, and close to pmax; a similar difference in p has now been found between CH and CD in-plane bending in (liquid) formic acid HCO2H
and DCO2H. Over the concentration range HCO2Na-4.5aq. to HCO2Na-15aq. concentration effects on the Raman and the infrared spectrum are generally very small; however, a concentration-dependent satellite band at 1622 cm-1 is taken to indicate the presence of some cation-anion pairs in intimate contact (of the order of 13% for HCO2Na-4.5D2O). ρ is almost the same for the satellite band and the main band (at 1593 cm-1), however. By contrast, solvent isotope effects on ρ are sometimes relatively
large. The spectrum of the solvent was therefore studied, too.
The Photoelectron Spectrum of 1-Bromonortricyclene
Authors: Della EW , Pigou PE , Livett MK , Peel JB
Published: September 2010

The He I photoelectron spectrum of 1-bromotricyclo[2.2.1.02.6] heptane (1- bromonortricyclene ) is compared with that of the parent alkane . Extensive conjugation between bromine
and alkane orbitals in the low ionization-energy range produces a complex band pattern which is adequately described by ab initio valence-electron molecular orbital calculations. Consequently 1-bromo-nortricyclene presents a rare example of an alkyl halide in which the halogen character is neither highly localized nor smeared over a high density of states.
The Stereochemistry of Organmetallic Compounds. XXV. The Stereochemistry of Displacements of Secondary Methanesulfonate and p-Toluene-sulfonate esters by Diphenylphosphide Ions. X-ray Crystal Structure of (5α- Cholestan- 3α-yl)diphenylphosphine Oxide
Authors: Roy Jackson W , Thomson RJ , Mackay.M.F .
Published: September 2010

Reactions of both axial and equatorial cholestan-3α- and -3β-yl mesylates and tosylates with sodium diarylphosphides give cholestanylphosphines in good yield and with complete inversion of stereochemistry. The stereochemistry has been established by an X-ray crystal structure of (5α-cholestan-3α-yl) diphenylphosphine oxide, and a general method for
distinguishing between axial and equatorial phosphines based on 31P N.M.R . spectra is presented. The monophosphines were used as ligands in asymmetric hydrogenation, but only low optical yields were obtained.
The Reaction of 2,3,5,6-Tetramethyl-4-nitrophenol with Nitrogen Dioxide
Authors: Hartshorn MP , Robinson WT , Vaughan JWJM
Published: September 2010

Reaction of 2,3,5,6-tetramethyl-4-nitrophenol (21) with nitrogen dioxide in benzene gives the four isomeric 2,4,5,6-tetranitrocyclohex- 3-enones (24)-(27), 2-hydroxy-4,5,6-trinitrocyclohex-3-enone (31), the C2-epimeric 6-hydroxy-2,4,5-trinitrocyclohex-3-enones (32) and (36) and the 2,6-dihydroxy-4,5-dinitrocyclohex-3-enone (33). X-ray crystal structures are reported for compounds (24), (25), (31), (32), (36) and the cyclopentenediol (37).
Flame Ionization of Silicon, Germanium and Tin
Authors: Ham NS , McAllister T
Published: September 2010

.When compounds of Si , Ge and Sn are added to 2/C6H6 diffusion flames, ions characteristic of the elements are detected in the burnt gases by mass spectrometry. The ions, which are attributed to charge exchange and proton transfer reactions of H3O+, may be divided into three categories, atomic ions, protonated monoxides and protonated oxyacids . Sn gives atomic ions and protonated monoxides, a similar result to Pb , but neither Si nor Ge give atomic ions. This may be a consequence of the lack of Si and Ge atoms in the burnt gases. Ge and Sn give a protonated monoxide, but Si does not. This observation leads to the suggestion that proton affinities of the Group 4a monoxides are in the order CO, SiO < H2O < GeO , SnO , PbO. Protonated silicic and germanic acids are observed in the burnt gases of Si - and Ge -containing flames, but no oxyacids were observed in Sn -or Pb -containing flames. This indicates that the proton affinities of both acids are greater than that of H2O.
The Structure of (1'RS, 2SR,3RS,4'SR)-2,3-(Cyclohex-2′-en-1′, 4′-ylene)-N-(4″-methyl-phenyl)succinimide
Authors: Hambley TW , Newsom IA , Sternhell S
Published: September 2010

A single-crystal X-ray structure determination gave the crystal and molecular parameters of\ (1′RS,2SR,3RS,4′SR)-2,3-(cyclohex-2′-en-1′,4′- ylene )-N-(4′-methylphenyl) succinimide , including the positions of all hydrogen atoms and the conformation of the 4′-methylphenyi group. The latter is possibly controlled by steric interactions between the ortho hydrogen atoms on the 4″-methylphenyl ring and the carbonyl oxygen atoms of the imide moiety. The six atoms of the imide moiety [O(10), C(9), N(8), C(13),
O(14) and C(5) on the ORTEP plot in Fig. 1] are planar within 0.04 Ǻ.
The 9-Decalyl and Related cations VII. Solvolysis of 3-(Cyclohex-1′-enyloxy)propyl p-Nitrobenzenesulfonate
Authors: Ferber PH , Gream GE , Stoneman TI
Published: September 2010

The solvolysis of 3-(cyclohex-1′-enyloxy) propyl p- nitrobenzenesulfonate (5) in ethanol buffered separately with sodium ethoxide and triethylamine and 2,2,2-trifluoroethanol buffered with triethylamine has been investigated. Kinetic determinations and product studies have been carried out. In ethanol buffered with sodium ethoxide , π-bond participation in the above ester occurs to the extent of 30%; this is raised to 84% when triethylamine is used as the buffering agent. With buffered trifluoroethanol as solvent, π-bond participation in the ester is complete; kunsat/ksat = 920 and a quantitative yield of cyclized products is obtained. Kinetic evidence indicates a lack of significant involvement of a lone pair on oxygen (enol ether system) in the solvolysis of the sulfonate ester; in trifluoroethanol , the compound solvolyses only 1.15 times more rapidly than does 4-(cyclohex-1′-enyl)butyl p-nitrobenzenesulfonate (2), its carbon analogue.
Further Aspects of the Reduction of Dithiocarbonates with Tributyltin Hydride and Deuteride
Authors: Conway RJ , Nagel JP , Stick RV , Tilbrook DMG
Published: September 2010

The reduction of 1,2:5,6-di-O-isopropylidene-3-O-(methylthio) thiocarbonyl-β-D-idose ,- talose, and -(3-2H) talose with tributyltin hydride and deuteride leads to the deoxy sugar and some deuterium-containing deoxy sugars. A modification of the normal procedure allows for reduction with tributyltin hydride generated in situ. As well, the reduction of some dithiocarbonates derived from glycosides of N-acetyl-D- glucosamine allows access to a variety of dideoxy and trideoxy sugars.
Synthesis of Some Furfural and Syringic Acid Derivatives
Authors: Jogia MK , Vakamoce V , Weavers RT
Published: September 2010

The formation of several derivatives of furfural and syringic acid, including some incorporating both components, is described. Assignments of the 1H and 13C n.m.r . spectra are also included.
Crystallographic Characterization of Isosevanine, a New Benzylisoquinoline Alkaloid
Authors: Bick IRC , Geewananda YA , Gunawardana P , Patrick VA , White AH
Published: September 2010

The characterization of a new benzylisoquinoline alkaloid, isosevanine, C18H15NO4, m.p. 148° isolated from Hedycarya angustifolia, by a single- crystal X-ray diffraction study is described. Crystals are monoclinic, P21/n, a 22.45(1), b 5.746(4), c 11.569(3) Ǻ, β 93.65(4)°, Z = 4; the structure was refined to a residual of 0.053 for 1016 independent 'observed' reflections.
Synthesis of Bridgehead-Bridgehead Substituted Bicycloalkanes
Authors: Della EW , Tsanaktsidis J
Published: September 2010

A convenient synthetic route to several bicycloalkanes bearing substitution at both bridgehead positions is described. The two-step procedure, which involves alkylation of the monoenolates of readily available cyclohexane diesters with 1,2-dihaloethane followed by a base-induced cyclization of the derived haloethylated product, was successfully applied to the synthesis of dimethyl bicyclo[2.2.2]octane- 1,4-dicarboxylate, dimethyl bicyclo[2.2.1]heptane-1,4-dicarboxylate and dimethyl bicyclo[3.2.1]octane-1,5-dicarboxylate. Additionally, it was found that the two latter diesters could be obtained in quite acceptable yields in a one-pot procedure through their corresponding cyclohexyl bisenolate precursors.
The Combination Reaction of CH3 and C6H5O
Authors: Lin CY , Lin CY , Lin MC , Lin MC
Published: September 2010

The kinetics and mechanism of the CH3+C6H5O reaction have been examined by means of the RRKM theory and kinetic modelling . Both the high temperature shock tube data for the production of cresols and the low temperature branching ratios (for production of cresols against methylcyclohexadienones , CH3C6H5O) derived from Mulcahy and Williams's data1 on the pyrolysis of di -t-butyl peroxide and phenol mixtures could be reasonably accounted for by the mechanism: ���������� CH3+C6H5O → CH3C6H5O → o- and p-CH3C6H4OH+M→ CH3C6H5OThe energy barrier for the thermal isomerization of CH3C6H5O to cresols was estimated to be ~ 132 kJ mol-1.
Conformational Energies and Structural Relaxation in Singly Bonded Silicon, Phosphorus and Sulfur-Compounds
Authors: Magnusson E
Published: September 2010

Conformational energy differences, structural relaxation and changes in bonding between different rotamers of silicon, phosphorus and sulfur compounds have been calculated by ab initio molecular orbital methods to permit systematic comparison between the compounds of first and second row elements. The results were obtained with polarized 3-21G and 4-31G basis sets on the series SiH3X, PH2X and SHX (X = BH2, CH3, NH2 and OH) and also on the rotamers of the second row hydrides Si2H6, P2H4 and S2H2. Bond length and bond angle relaxation and conformational energy differences for the Si -, P- and S-containing molecules are 30-50% smaller than in the compounds of the first row elements.
Photooxidation at Platinum Colloidal TiO2 Aqueous-Solution Interfaces. I. Ethylenediaminetetraacetic Acid and Related-Compounds
Authors: Furlong DN , Wells D , Sasse WHF
Published: September 2010

The photooxidation of ethylenediaminetetraacetic acid ( edta ) and related glycine derivatives, at Pt/TiO2/aqueous solution interfaces, has been monitored via the production of hydrogen and carbon dioxide. Yields are consistent with the exhaustive oxidation of methoxycarbonyl groups and the rate varied with the number and distribution of such groups. A photooxidation pathway is proposed which involves the oxidation of intermediate carbonium ions. Plausible molecular intermediates, such as formic acid and formaldehyde in the case of edta , have been shown in separate experiments to be photooxidized according to the proposed pathway. The maximum rate of oxidation for each donor depends on its oxidation potential and
its tendency to adsorb on TiO2 surfaces. Desorption due to pH increase, as well as consumption of the donor, causes the rate to decline rapidly with illumination time. Acetic and malonic acids gave some hydrogen but underwent mainly (> c. 80%) photo-Kolbe decarboxylation to yield carbon dioxide and methane. By contrast the oxidation of oxomalonic, pyruvic and lactic acids proceeded mainly via a H2 producing pathway similar to that established for edta. The oxidation of pyruvic and lactic acids ceased at a yield of one mole of CO2 per mole of acid.
Synthesis of the Lichen Depsides Miriquidic Acid and Normiriquidic Acid
Authors: Elix JA , Jayanthi VK
Published: September 2010

The total synthesis of the lichen depsides miriquidic acid (1) and normiriquidic acid (2) is reported. The latter depside has been shown to co-occur with miriquidic acid in the lichen Lecidea leucophaea ( Flk .) Nyl . by chromatographic comparisons.
Studies of Australian Soft Corals. XXXVIII. Structure Determination of Several Diterpenes Derived From a Cespitularia Species (Coelenterata, Octocorallia, Xeniidae)
Authors: Bowden BF , Coll JC , Gulbis JM , Mackay MF , Willis RH
Published: September 2010

The structure elucidation
of three new diterpenes , isolated from a soft coral Cespitularia species, is reported. Two of the metabolites
(3), (7E,11E,1R*,3aS*,4S*,12aR*)-11-iso-propyl-1,4,8-trimethyl- 1,2,3,3a,4,5,6,9,10,12a-decahydrocyclopentacycloundecene-1,4-diol, and (4), (4E,7E,11E)-11-isopropyl-1,4,8-trimethyl-1,2,3,3a,6,9,10,12a-octahydrocyclopentacyclo-undecen-1-ol, are shown to possess a further cyclized cembrane skeleton, the structure of (3) being determined by a single-crystal X-ray determination while that of (4) was deduced from spectral comparison with (3). The structure of the
remaining diterpene (5) (4,5-deoxyneodolabelline) was deduced from 1H and 13C n.m.r . spectroscopic studies and shown to be closely related to the recently reported clavularian metabolite neodolabelline (8). An authentic sample of neodolabelline (8) was chemically transformed into (5) by the action of a zinc-copper couple establishing the absolute structure of (5).
The Indans Formed by Dimerization of Some Aromatic Terpenoids
Authors: Carman RM , Vandonge n
Published: September 2010

Previous work upon the dimerization of carvacrol derivatives to form indans is corrected.
The Chemical Iodination of Silver
Authors: Campbell GD , Lincoln FJ , Ritchie IM
Published: September 2010

Kinetic experiments are reported on the chemical formation of AgI layers on polycrystalline silver substrates. The AgI layers, up to several micrometres in average thickness, were grown under ambient conditions by reacting a rotating silver disc with solutions of iodine dissolved in ethanol and with aqueous triiodide solutions. The morphology and structural identity of the AgI layers were determined by scanning electron microscopy and powder X-ray diffraction, respectively. Depending upon the growth conditions employed, either porous or compact AgI deposits could result, and thus the rate of formation of AgI could be limited by a diffusion step in solution, or by some slower transport step across the layers. The AgI layers were inhomogeneous, and often consisted of discrete crystallites. Thus, the metal oxidation theories developed for planar and isotropic product layers could not be applied to the formation of AgI layers under ambient conditions.
Synthesis of Analogs of GABA .15. Preparation and Resolution of Some Potent Cyclopentene and Cyclopentane Derivatives
Authors: Allan RD , Fong J
Published: September 2010

A series of cyclopentene and cyclopentane analogues of GABA has been prepared utilizing a thermal cis -trans isomerization of the phthalimido β,γ -unsaturated acid (10) as the key step to obtain trans-4- aminocyclopent-2-ene-1-carboxylic acid (7). Resolution of
some of the potent GABA analogues, in particular (+)-(4S)- and (-)-(4R)-4- aminocyclopent-1-ene-1-carboxylic acid (5), has been achieved by crystallization of isopropylideneribonolactone esters or pantolactone esters of the phthalimido -protected intermediates.
Organomercury Compounds .XXVIII. The Synthesis and 199Hg N.M.R-Spectra of Some Unsymmetrically Dimercurated Arenes
Authors: Deacon GB , Oconnor MJ , Stretton GN
Published: September 2010

Mercuration of 1-methoxy-2-nitrobenzene (1) with mercuric trifluoroacetate (mole ratio 1 : 1) in trifluoroacetic acid yields 1- methoxy-2-nitro-4-(trifluoroacetatomercurio)benzene (2). With a 1 : 2 mole ratio, (2) and 1-methoxy-2-nitro-4,6- bis(trifluoroacetatomercurio)benzene (3) are obtained, and, with a 1:4 ratio, (3) and a little 1-methoxy-2-nitro-3,4- bis(trifluoroacetatomercurio)benzene (4). are obtained. 2-Nitrophenol (5) with mercuric trifluoroacetate (mole ratio 1 : 2) gives 2-nitro- 4,6-bis(trifluoroacetatomercurio)phenol (6), and vanillin (7) yields 5,6-bis(trifluoroacetatomercurio)vanillin (8). Compound (8) has been converted into 5,6-di(chloromercurio)- and 5,6- di(bromomercurio)vanillin [(9) and (10)]. 199Hg,199Hg spin-spin coupling constants have been determined
s 6500-8200 Hz for 3JHg,Hg of (8)- (10), 2100-2200 Hz for 4JHg,Hg of (3) and (6), and 858 Hz for 5JHg,Hg of 4- methoxy-2,5-bis(trifluoroacetatomercurio)benzoic acid (11).
Abinitio Calculations of the Barriers to Rotation in Some Monosubstituted Benzenes
Authors: Marriott S , Topsom RD
Published: September 2010

Theoretical calculations at the ab initio level have been made of the twofold rotational barriers of some monosubstituted benzenes, and the effects both of basis set and of geometry optimization have been examined. Values at the STO-3G//STO-3G level are in good agreement with experiment. The use of split-valence sets, even with geometry optimization, is much less satisfactory, and this may be related to an overestimation of π-electron transfer between the substituent and the benzene ring.
Geometry Change on Ionization. Calculation of IV-IA Relaxation Energies for NH3, N2H4 and CH3NH2
Authors: Peel JB
Published: September 2010

Ab initio calculations on the NH3, N2H4 and CH3NH2 molecules and their respective ground- state cations represent the experimentally observed adiabatic and vertical ionization energies with reasonable accuracy. The unusually large IV - IA difference energy for N2H4 is a measure of the considerable change in geometry accompanying ionization. The calculated value of this relaxation energy at the MP3/6-31G** level is 2.3 eV , rather higher than the two experimental measurements of 1.55 eV , based on the band profile of the ultraviolet photoelectron spectrum, and 1.6-1.8 eV , determined from ion-molecule equilibrium measurements. The smaller IV-IA values for NH3 and CH3NH2 are calculated more accurately. Theoretical vibration frequencies are also obtained for the molecular cations.
Characterization of Tris(Diselenocarbamato)Cobalt(III) and Pentakis(Diselenocarbamato)Dicobalt(III) Complexes by Electrochemical, Cobalt-59 N.M.R. and Mass-Spectrometric Techniques. Comparisons With Dithiocarbamate Analogs
Authors: Bond AM , Colton R , Mann DR , Moir JE
Published: September 2010

A series of Co(RR′dsc)3 and [Co2(RR′dsc)5]+ complexes (R, R′ = two alkyl groups or one heterocyclic group; dsc = NCSe2) have been synthesized and their redox behaviour, chemical reactivity and spectroscopic properties compared with the corresponding dithiocarbamate (RR′dtc) complexes. Electrochemical oxidation of Co(RR′dsc)3 in dichloromethane at platinum electrodes occurs at potentials about 0.34 V
less positive than for Co(RR′dsc)3. The formally cobalt(IV) complexes [Co(RR′dsc)3]+ can be identified as a product which is then converted into [Co2(RR′dsc)5]+ via dimerization and an internal redox reaction. Despite the enhanced thermodynamic stability implied by the redox potentials, [Co(RR′dsc)3]+ has similar kinetic stability to the analogous dithiocarbamate complexes. Co(RR′dsc)3 is reduced at fairly negative potentials on both platinum and mercury electrodes with extremely rapid loss of [RR′dsc]-. [Co(RR′dsc)3]- is therefore thermodynamically and kinetically more unstable than [Co(RR′dtc)3]- . The [Co2(RR′dsc)5]+ complexes are also more readily oxidized and harder to reduce than the sulfur analogues. Oxidation of [Co2(RR′dsc)5]+ produces [Co2(RR′dsc)5]2+ at low temperatures and fast scan rates, but no stable reduced form of the dimer is accessible on the voltammetric time scale examined. The reduction process for the dimer is consistent with the reaction [Co2(RR′dsc)5]+ +e- → Co(RR′dsc)3+ Co(RR dsc)2. Electrochemical oxidation data obtained at mercury electrodes for the diselenocarbamate complexes are complicated by adsorption but are similar to that found at platinum electrodes. This contrasts with the dithiocarbamates where a mercury electrode specific pathway is observed. Cobalt-59 n.m.r. spectroscopy in dichloromethane shows the non- equivalence of the two cobalt atoms in [Co2(RR′dsc)5]+. The chemical shifts for Co(RR′dsc)3 complexes exhibit similar substituent effects to the dithiocarbamates in cobalt-59 n.m.r. measurements as was the case in oxidative electrochemistry. Cobalt-59 n.m.r. spectroscopy and mass spectrometry demonstrate that exchange, substitution and redox reactions can lead to the formation of mixed ligand diselenocarbamate complexes and mixed dithiocarbamate/diselenocarbamate complexes for both the cobalt(III) monomers and dimers.
Imidazo[1,2-B]Pyridazines. I. Some 3-Alkoxy-6-Halogeno-2-Phenyl-(and 4′-Substituted Phenyl)Imidazo[1,2-B]Pyridazines and 3-Methoxy-2,6-Diphenylimidazo[1,2-B]Pyridazine
Authors: Barlin GB
Published: September 2010

A series of 3-alkoxy-6-halogeno-2-phenyl(and 4′-substituted phenyl) imidazo [1,2-b] pyridazines (1) and 3-methoxy-2,6- diphenylimidazo [1,2-b] pyridazine have been prepared from the relevant pyridazin-3-amines and arylglyoxals, followed by O- alkylation of the corresponding imidazo [1,2-b]pyridazin-3(5H)-ones with diazoalkanes. 6- Chloro-3-methoxy-2-phenylimidazo[2,1-a] phthal-azine was prepared similarly.
The Conformation of Some 1,1,2,2-Tetraacylethanes in the Solid-State: Crystal-Structures of 1,1,2,2-Tetrabenzoylethane, 1,2-Diacetyl-1,2-Dibenzoylethane and 1,1,2,2-Tetraethoxycarbonylethane
Authors: Cannon JR , Patrick VA , White AH
Published: September 2010

The crystal structures of 1,1,2,2-tetrabenzoylethane (3), 1,2-diacetyl- 1,2-dibenzoylethane (4) and 1,1,2,2-tetraethoxycarbonylethane (tetraethyl ethanetetracarboxylate ) (5) have been determined by X-ray diffraction from diffractometer data at 295 K and were refined by least-squares techniques to residuals of 0.050 (1077 'observed' reflections), 0.056 (3020) and 0.041 (480), respectively. Crystals of (3) are triclinic, Pī , Z 1, a 6.145(2), b 9.002(3), c 11.261(3) Ǻ; α 101.91(3), β 91.88(3), γ 105.94(3)°. Crystals of (4) are also triclinic, Pī , Z 2, a 17.119(5), b 7.210(1), c 7.175(2) Ǻ, α 89.59(2), β 72.92(2), γ 87.87(2)°. Crystals of (5) are tetragonal, P42/n, Z 4, a 17.748(6), c 5.515(1)Ǻ. In the solid state each compound exists in the keto form which adopts the antiperiplanar conformation about the central carbon-carbon bond.
The Hydroxy Derivatives of 2,5-Diphenyl-1,3,4-Oxadiazole
Authors: Jacobsen NW , Philippides AE
Published: September 2010

An unambiguous synthesis for each of the monohydroxy derivatives of 2,5-diphenyl-1,3,4-oxa-diazole is reported.
N.M.R. Studies of Phosphine Adducts of Mercury and Cadmium Xanthates and Halo Xanthates: Crystal and Molecular Structures of Cd(S2COPri)2PPh3, Hg(S2COPrI)2PPh3 and Hg(S2COPrI)2p(c-C6H11)3
Authors: Abrahams BF , Corbett M , Dakternieks D , Gable RW , Hoskins BF , Tiekink ERT , Winter G
Published: September 2010

Phosphorus-31, cadmium-113 and mercury-199 n.m.r. techniques have been used to study adduct formation, in solution, between phosphines and cadmium and mercury xanthates and halo xanthates. The crystal structures of the 1:1 phosphine adducts Cd (S2COPri)2PPh3, Hg(S2COPri)2PPh3 and Hg(S2COPri)2P(c-C6H11)3 have been determined.
Decarboxylation of Bridgehead Carboxylic Acids by the Barton Procedure
Authors: Della EW , Tsanaktsidis J
Published: September 2010

Reductive decarboxylation of a series of bicyclic and polycyclic acids in which the carboxyl group is attached to the bridgehead position has been investigated. Conversion of the acids into thiohydroxamic esters occurs via reaction of the derived acid chlorides with N- hydroxypyridine-2-thione. Decomposition of the esters proceeds smoothly in boiling benzene in the presence of t-butyl mercaptan to give the reduced product in high yield. The procedure appears to be generally applicable, and is unaffected by functional groups such as esters and acetals.
A Synthesis of 1-Methoxyisoquinoline-3,4-Diamine and Some Derived Imidazo[4,5-C]Isoquinolines
Authors: Deady LW , Kachab EH
Published: September 2010

A convenient synthesis of 1-methoxyisoquinoline-3,4-diamine is described. From this, one-carbon bridging units were used to prepare the angular imidazo [4,5-c] isoquinoline system containing 2-aryl, 2-thio and 2-amino substituents . From the latter two, further ring formation between substituent and imidazo nitrogen was investigated.
Cluster Chemistry. XLVII. X-Ray Crystal Structure of OsPt2(μ-CO)3(CO)2(PPh3)3
Authors: Bruce MI , Snow MR , Tiekink ERT
Published: September 2010

The crystal structure of OsPt2(μ-CO)3(CO)2(PPh3)3 has been determined by single-crystal X-ray diffraction techniques. Crystals are triclinic, space group Pī with unit cell dimensions a 13.593(4), b 15.839(4), c 12.633(8) Ǻ, α 102.97(3), β 108.18(2), γ 84.86(3)° with Z2. The structure was refined by a full-matrix least-squares procedure on 5896 reflections [I ≥ 2.5σ(I)] to final R 0.028 and Rw 0.034. A triphenylphosphine ligand binds each of the metal atoms disposed at the corners of a triangle. Each metal-metal bond is spanned by a bridging carbonyl group. The coordination about the osmium atom is completed by two terminal carbonyl groups.
Crystal-Structure of Trimethylphosphine Oxide
Authors: Engelhardt LM , Raston CL , Whitaker CR , White AH
Published: September 2010

The structure of [P(O)Me3] has been determined by X-ray diffraction: crystals are monoclinic, space group C2/m with a 10.86(1), b 9.026(6), c 5.394(4) Ǻ, β 92.09(8)° with Z =4. Molecules lie on crystallographic mirror planes; P-O 1.489(6), P-C 1.772(6) and 1.770(10)Ǻ, <O-P-C 112.2(2) and 114.0(4)°, <C-P-C 105.6(3) and
106.2(3)°.
Detection of the 1,2-Didehydronaphthalene to 1H-Indenylidenecarbene Rearrangement by Intramolecular Trapping in a Flash Vacuum Pyrolytic Reaction
Authors: Brown RFC , Coulston KJ , Eastwood FW , Saminathan S
Published: September 2010

Flash vacuum pyrolysis of 9-methyl-1,3-dihydronaphtho[1,2-c]furan-1,3-dione (8) at 750-880� gave exclusively 1H-cyclopent[ cd ]indene (9) and of 8-methyl-1,2-dihydrocyclobuta[a]naphthalene-1.2-dione (10) at 600-840� gave a mixture of (9) and acenaphthylene. Acenaphthylen-4-ol (12) was synthesized and found to be stable to flash vacuum pyrolysis over thetemperature range 600-900�. These findings are discussed in relation to the rearrangement described in the title.
Metal Template Reactions. XXIII. Synthesis of Macrocyclic Amide and Ester Complexes Via 1,1′-Oxalylbisisatin
Authors: Black DS , Moss GI
Published: September 2010

1,l'-Oxalylbisisatin (7) has been prepared and converted readily into a wide range of glyoxylic esters and amides (10) from which the macrocyclic metal complexes (11)-(16) have been obtained.
The Preparation of Some Octenyl Sulfides From Oct-1-en-3-Ol and Oct-2-en-1-ol
Authors: Binns MR , Haynes RK , Lambert DE , Schober PA , Turner SG
Published: September 2010

(E)- and (Z)-1-(Pheny1thio)oct-2-ene, (E)-1-(methylthio)- and 1-(t-butylthio)-oct-2-ene, S-[(E-oct-2-enyl] N,N- dimethylthiocarbamate , S-[(E)-oct-2-enyl] N,N- dimethylthiocarbamate , (E)-(oct-2-enylthio) benzothiazole , and S-[(E)-oct-2-enyl] N,N,N',N'- tetramethylphosphorodi - amidothioate have been prepared by nucleophilic substitution reactions and [1,3]- and [3,3]-sigma- tropic shifts involving intermediates prepared from oct-1-en-3-ol and (E)- and (Z)-oct-2-en-1-ol.
Copper(II) and Nickel(II) Complexes of Pentaaza Macrocyclic Ligands
Authors: Osvath P , Curtis NF , Weatherburn DC
Published: September 2010

The preparations of the pentaazamacrocyclic ligands 1,4,7,10,13-pentaazacyclopentadecane, cpad , l,4,7,l0,13-pentaazacyclohexadecane, ched , l,4,7,l0,14-pentaazacycloheptadecane, chad , 1,4,7,11,14-pentaazacycloheptadecane, cnad , 1,4,7,11,15-pentaazacyclooctadecane, cnad , 1,4,8,11,15-pentaazacyclooctadecane, cnad , 1,4,8,12,16-pentaazacyclononadecane, cnad , and 1,5,9,13,17-pentaazacycloeicosane, ceic , as well as the new linear pentaamine N-(3-aminopropy1)- N'-[3-[(3-aminopropyl)amino] propyl ]propane-1,3-diamine, tpah , are described. Copper(II) and nickel(II) complexes of the above ligands have been prepared and characterized. The nickel(II) complexes of the smaller macrocycles and the linear pentaamine contain NiII in a tetragonally distorted octahedral environment in the presence of coordinating anions or in aqueous solution but the [Ni( cnad )]2+ and [Ni( ceic )]2+ cations are five-coordinate both in the solid state and in aqueous solution. The copper(II) complexes of the macrocyclic pentaamines appear to be square-pyramidal on the basis of their electronic spectra, whereas the complex [cu( tpah )]2+ is probably trigonal- bipyramidal.
Synthesis of Lichen para-Sphaerophorol Depsides
Authors: Elix JA , Wardlaw JH
Published: September 2010

The total synthesis of the lichen depsides sphaerophorin
(I), 4-O-demethylsphaerophorin (2),isosphaeric acid (3), hyperlatolic acid (4) and isohyperlatolic acid (5) is described.
Energetic Contributions to the Two-Electron Bond: A Simplified Group Function (SGF) Analysis
Authors: Schipper PE
Published: September 2010

The group function (GF) formalism coupled with the limit in which intergroup electron interchange symmetry is rigorously neglected (the simplified group function (SGF) approach) is shown to lead to a resolution of intergroup bonding as an effective power series in overlap density. The successive orders are shown to correspond to a concomitant resolution into traditional bonding contributions: zeroth order leads to the conventional excitonic description (no electron transfer or interchange); first-order terms may be interpreted as dative bonding, in which electron transfer configurations mix with the excitonic states; and finally, second-order terms correspond directly to the incorporation of electron interchange symmetry and hence to pure covalent bonding. A conceptual parallelism of the division of long range (static, inductive and dispersive) interactions with short range (ionic, dative and covalent) interactions is drawn to emphasize the unity of these apparently disparate limits in the SGF/GF analysis. Explicit application to the archetypical two-electron bond highlights the conceptual simplicity of the approach, and is compared to a commensurate MO and VB analysis expressed in terms of the same integrals. The results show clearly why such a simple resolution is difficult to extract from MO and VB approaches, which are philosophically biased towards the strong bonding limit.
Thermal Degradation of Polymers. III. Thermal Degradation of a Compound Which Models the Head-to-Head Linkage in Poly(Methyl Methacrylate)
Authors: Holland KA , Rae ID
Published: September 2010

As a model for a poly(methyl methacrylate ) chain which contains a head-to-head unit, the thermal degradation of tetramethyl 2,4,5,7-tetramethyloctane-2,4,5,7-tetracarboxylate has been studied. The meso compound degraded at 210� to give seven products which have been characterized by spectroscopic techniques and synthesized by unambiguous routes. The products resulted from reactions which followed thermal rupture of the central C-C bond of the model compound, thus supporting the proposal that head-to-head units are important in the thermal degradation of poly(methyl methacrylate ).
Regioselective Synthesis of Secondary Allyl Chlorides
Authors: Boughdady NM , Chynoweth KR , Hewitt DG
Published: September 2010

We have developed high-yielding regiospecific conversions of internal secondary allylic alcohols into rearranged or unrearranged allylic chlorides using thionyl chloride in ether at -70�C or hexachloroacetone /triphenylphosphine at - 70�C respectively. The mechanisms of the reactions are discussed.
The Minor Iridoid Glucosides of Barleria lupulina: Isolation, Crystal Structure and Plant Growth-Inhibiting Properties of 6-O-Acetylshanzhiside Methyl Ester
Authors: Byrne LT , Sasse JM , Skelton BW , Suksamrarn A , White AH
Published: September 2010

The minor iridoid glucosides present in the aerial parts of Barleria lupulina Lindl. ( Acanthaceae ) have been identified as ipolamiidoside (7) and the new compound 6-O-acetylshanzhiside methyl ester (3). The structure of (3) was determined by spectroscopic and chemical methods, and was confirmed by a single-crystal X-ray structure determination. Crystals of (3) are orthorhombic P212121, a 43.75(1), b 8.151(3), c 5.695(2) �, Z 4. The crystal structure was determined at 295 K from diffractometer data [I528 reflections with I > 3σ(I)] and refined to a residual of 0.043. Shanzhiside methyl ester (1) and its 6-Oacetyl (3), 8-Oacetyl (2) and 6,8-O,O-diacetyl (4) derivatives, all of which occur in Barleria lupulina, have been found to inhibit the growth of wheat embryos.
Cobalt(II) and Cobalt(III) Complexes of Pentaaza Macrocyclic Ligands. Isomeric Composition and Hydrolysis Reactions of the Complexes of Eight Ligands With 15-Membered to 20-Membered Macrocyclic Rings
Authors: Curtis NF , Osvath P , Weatherburn DC
Published: September 2010

Synthesis and characterization of cobalt(III) complexes of the pentaaza macrocyclic ligands 1,4,7,10, 13-pentaazacyclopentadecane, ( cpad ), 1,4,7,10,13-pentaazacyclohexadecane, ( ched ), 1,4,7,10,14-pentaazacycloheptadecane, ( chad ), 1,4,7,11,14-pentaazacycloheptadecane, ( chbd ), 1,4,7,11, 15-pentaazacyclooctadecane, ( coad ), 1,4,8,11,15-pentaazacyclooctadecane, ( cobd ) are described. Of the different isomeric forms possible for each complex only one geometric isomer and one or two of the possible diastereoisomers have been isolated. The products of the induced acid hydrolysis reactions of the bromo and chloro complexes with these ligands have been identified by means of 13C n.m.r. spectroscopy. Nitrato complexes are commonly produced when the reaction proceeds in nitrate media. The reactions of the [Co( cpad )X]n+ and [Co( chbd )X]n+ complexes proceed with the apparent inversion of a coordinated nitrogen in strongly acid media. Cobalt(II) complexes of the ligands 1,4,8,12,16-pentaazacyclononadecane ( cnad ) and 1,5,9,13,17-pentaazacycloeicosane (ceic) were prepared. These complexes could not be oxidized to cobalt(III) complexes and the available evidence suggests that they are five-coordinate square-pyramidal complexes in the solid state and in solution.
Heterocyclic Variants of the Purine System. III. Derivatives of Oxazolo[5,4-e]-1,2,4-Triazine and Oxazolo[4,5-e]-1,2,4-Triazine, Two New Heterocyclic Ring Systems
Authors: Jacobsen NW , Philippides AE
Published: September 2010

Representative derivatives of the [5,4-e] and [4,5-e] oxazolo-1,2,4-triazine ring systems were prepared by cyclodehydration of the respective 5-acylaminotriazin-6-ones and 6-acylaminotriazin-5-ones. 5-Methylthio-3-phenyltriazin-6-amine also gave a 6-anilino derivative of the [5,4-e] series when treated with phenyl isocyanate, but the method was not a successful route to the [4,5-e] series.
Convenient Preparation of Halogenoborane-Dimethyl Sulfide Complexes
Authors: Bolton R , Gates PN , Jones SAW
Published: September 2010

.Details are reported of the synthesis of mono- and di- halogenoboranes as their dimethyl sulfide complexes. The analysis of such mixtures by 11B n.m.r. spectroscopy and some applications of these complexes are described.
Crystal and Molecular Structure of Tris(Ethane-1,2-Diamine)Osmium(III) Trifluoromethanesulfonate Monohydrate
Authors: Lay PA , Mclaughlin GM , Sargeson AM
Published: September 2010

The crystal and molecular structure of racemic [Os(en)3] (CF3SO3)3.H2O has been determined. The [Os(en)3]3+ ion adopts a le ξob configuration and has approximate C2 symmetry with an Os-N(av.) bond length of 2.11 � and a bite angle for the chelate of - 82�. The previously recorded structure of the [Os(en-H)2(en)]2+ ion in which two deprotonated ethane-1,2-diamine ligands adoptoa cis configuration of the two amido donors, and in which the OsIV -N( amido ) bonds (1.90 �) are much shorter than the Os-N(amine) bonds, 2.11 ( cis ), 2.19 (trans), along with the present structure indicates a bond order > 1 for the osmiumo amido bond. The normal Os-N bond lengths fall into well defined ranges OS-NR3 (2.11-2.14 �), Os=NR2- (~1.90 �),Os=NR2 (- 1.70 �) and Os=N3-(- 1.58-1.63 �). These single bond lengths are more affected by trans effects than the formal oxidation state of the osmium centre.
An Oxygen-Nitrogen Donor Macrocycle Immobilized on Silica Gel. A Reagent Showing High Selectivity for Copper(II) in the Presence of Cobalt(II), Nickel(II), Zinc(II) or Cadmium(II)
Authors: Dudler V , Lindoy LF , Sallin D , Schlaepfer CW
Published: September 2010

A 17-membered O2N3-donor macrocycle has been appended to a derivatized silica gel substrate, and the binding and selectivity properties of the functionalized surface towards CO11, Ni11 CU11, Zn11 and Cd11 in aqueous solution have been investigated. Metal uptake was found to be concentration-dependent with the maximun (saturation) loading capacity in all cases being less than the 'theoretical' amount based on the calculated degree of polymer functionalization present. Metal loading and leaching both occurred readily in aqueous media; the loading studies were performed at near-neutral pH whereas metal leaching was carried out by using either dilute (hydrochloric) acid or aqueous ammonia solution. The functionalized silica underwent no degradation during repeated loading/leaching cycles, and, under similar conditions, its binding capacity is highest for CU11 relative to the other ions investigated. The observed binding order was CO11 < Ni11 < CUII > ZnIIand this sequence parallels the respective log K values for the complexes of the free macrocycle. However, the loading order of ZnII > CdII which was observed is the opposite to the corresponding log K values for the unattached complexes. Steric effects involving the silica backbone appear to influence the binding in this case. The insolubilized product may be used to remove selectively CuII in the presence of the other ions mentioned above.
Substituent Effects in the Reactions of Some Polysubstituted 4-Hydroxy-4-methylcyclohexa-2,5-Dienones With Hydroxide Ion; X-Ray Structure Analyses of 2,5,6-Tribromo-3,4-dihydroxy-4-methylcyclohexa-2,5-dienone and 3,4-Dibromo-5-methyl-5-nitroacetylfuran-2(5H)-one
Authors: Gray MJ , Hartshorn MP , Robinson WT , Vaughan J
Published: September 2010

Reactions of the 2,3,5,6-substituted 4-hydroxy-4-methylcyclohexa-2,5-dienones (6a), (6b), (7a) and (7b) with hydroxide ion give 3,4-dihydroxy dienones (9a), (9b), (10) and (11). In contrast, hydroxide ion treatment of the substituted nitro dienone (8), followed by acidification, gives the substituted furan-2(5H)-one (12). The effect of substituents on the course of the reactions is discussed. X-ray structure determinations for compounds (9a) and (12) are reported.
Lewis-Base Adducts of Group-11 Metal(I) Compounds. XXXI. Reaction of 2,6-Bis[1-phenyl-1-(pyridin-2-Yl)ethyl]pyridine (L), and Copper(I) Halides in Acetonitrile: Structural Characterization of Salts of the [(MeCN)Cu(meso-L)]+ Cation
Authors: Canty AJ , Engelhardt LM , Healy PC , Kildea JD , Minchin NJ , White AH
Published: September 2010

Reaction of 2,6-bis[l-phenyl-1-(pyridin-2-yl)ethyl]pyridine, L, with copper(1) chloride, bromide, and iodide in acetonitrile solution has been shown to yield salts, structurally characterized by single-crystal X-ray diffraction methods as [( MeCN ) CuL ]+ [ ClCuCl ]-, (1), [( MeCN ) CuL ]+2 [XCuX2CuX]2-, X = Br (2), I (3) (both isomorphous ), all as yellow needles, and a form of (3), orange blocks, as the hemiacetonitrile solvate, (4), [( MeCN ) CuL ]+2 [IcuI2Cul]2-. MeCN . The same cation is common to all four species, containing four-coordinate copper(r), with L as meso -tridentate ligand; in (4), the most precisely defined example, Cu-N( MeCN ) is 1.919(5) �, the shortest copper(1) acetonitrile distance known, while Cu-N(L) are 2.065(5)-2.073(5) �. The reason for non-formation of species of the type [ LCuX ] appears to lie in the tridentate ligand conformation which permits coordination of acetonitrile but not larger halide species.
Tropical Marine Algae. I. New Halogenated Monoterpenes From Chondrococcus hornemannii (Rhodophyta, Gigartinales, Rhizophyllidaceae)
Authors: Coll JC , Wright AD
Published: September 2010

Four linear halogenated monoterpenes: (2Z,6E)-1,8-dichloro-3-chloromethyl-7-methylocta- 2,6-diene (1), (E)-1,2-dibromo-3-chloromethylene-7-methyloct-6-ene (2), (Z)-1-chloro-3-chloromethyl-7-methylocta-2,6-diene (3) and (Z)-1,6-dichloro-3-chloromethyl-7-methylocta-2,7- diene (4), and two epimeric bicyclic monoterpenes (2R*,3(8) E,4S*,6R*)-6-bromo-2-chloro-1,4- oxido-3(8)- ochtodene (5) and (2S*,3(8)E,4S*,6R*)-6-bromo-2-chloro-1,4-oxido-3(8)- ochtodene (6) have been isolated from the red alga Chondrococcus hornernannii collected on the Great Barrier Reef, Australia. The structures were assigned on the basis of 1H and 13C n.m.r. spectroscopic studies, and provide another example of the co-occurrence of cyclized and linear halogenated monoterpenes in the same species.
Five New Fully Substituted Depsides From the Lichen Pseudocyphellaria pickeringii
Authors: Elix JA , Wilkins AL , Wardlaw JH
Published: September 2010

The new depsides 2'- O- methylphenarctin (6), 1'-chloronephroarctin (7), 2'- O- methylpseudo-cyphellarin A (3), isopseudocyphellarin A (8) and 2'- O- methylisopseudocyphellarin A (9), have been isolated from New Zealand collections of the lichen Pseudocyphellaria pickeringii . The structures of the new metabolites were initially deduced from an analysis of mass spectral and 1H n.m.r. data and subsequently confirmed by unambiguous syntheses.
A One-Step Synthesis of the Depsidone Furfuric Acid: Evidence for an Artifact in the Isolation From a Lichen
Authors: Elix JA , Evans JE , Parker JL
Published: September 2010

The structurally unique depsidone furfuric acid (1) has been prepared in one step by the acid-catalysed alkylation of methyl p- orsellinate
(6) or of atranorin (4) with physodalic acid (7). This mode of synthesis gives credence to the proposal that (1) is an artefact of the isolation procedure rather than a true metabolite of the lichen Pseudevernia furfuracea .
Dehydrogenation of 4,5-Disubstitued 9,10-Dihydrophenanthrenes
Authors: Cosmo R , Sternhell S
Published: September 2010

Dehydrogenation rates of four 4,5-disubstituted 9,l0-dihydrophenanthrenes to the corresponding phenanthrenes by 10% palladium on charcoal for the substituents, H, OCH3, F and CH3, appear to be related to the size of the substituents. The preparation of three new phenanthrenes, viz. 4,5-dichlorophenanthrene, 4,5-difluoro-phenanthrene and 4,5-bis( trifluoromethyl ) phenanthrene, is described. Treatment of mesitylene with either 10% palladium on charcoal at reflux or 2,3-dichloro-5,6- dicyano-1,4-benzoquinone gives an appreciable yield of mesityl(3',5'-xylyl)methane.
Terpenoids From the Brown Alga Cystophora moniliformis
Authors: Vanaltena IA
Published: September 2010

The alga Cystophora moniliformis contains two new bisnorsesquiterpenes, (5E,9E)-5,6-epoxy-6,10,14-trimethylpentadeca-9,13-dien-2-one (3) and its cyclized derivative (4), and the (2E) and (2Z) isomers of geranylgeranal epoxide, (5) and (6), respectively. The structures of the new compounds were deduced by spectroscopic means. Geranylacetone (1) was the major metabolite present in the alga.
The Selective Monobenzylidenation of Some Monosaccharides and Their Derivatives With α,α-Dimethoxytoluene
Authors: Patroni JJ , Stick RV , Skelton BW , White AH
Published: September 2010

The treatment of some monosaccharides and their derivatives with a,a-dimethoxytoluene and an acid catalyst in dimethylformamide at about 80° can lead to selective benzylidenation , e.g. methyl a-D- mannopyranoside gives mainly methyl 4,6-Obenzylidene-a-D-mannoside, together with two other minor monobenzylidene derivatives (2,3-) and two minor dibenzylidene derivatives (2,3:4,6-). The treatment of various other pyranoses and pyranosides is also described. As well, a 1H n.m.r . study of the acid transformation of some of the above α-D- mannosides is reported, together with a single-crystal X-ray diffraction structure determination of a novel monobenzylidene derivative, namely methyl (S)- 2,3-O-benzylidene-α-D-mannopyranoside.
A Study of the Photochemistry of Benzobicyclo[2.2.2]octan-2-ones
Authors: Beckwith PLM , Ghisalberti EL , Jefferies PR , Raston CL , White AH
Published: September 2010

The anti- and syn-3-methyl isomers of 5,8-dimethoxy-1,3-dimethyl-3,4-dihydro-1,4-ethanonaphthalen-2(1H)-one (2) and (3) and the 1,3,3- trimethyl analogue (4) were prepared from the Diels -Alder adduct of benzoquinone and 1,3-dimethylcyclohexadiene. The photochemistry of each has been studied and the structures of several photoproducts have been assigned. One of the products from irradiation of (3) was found by X-ray analysis to be a 1,4-disubstituted 1,2,3,4- tetrahydronaphthalene [methyl 2-(5′,8′-dimethoxy-4z′-methyl-1′,2′,3′,4′-tetrahydronaphthalen-1′-yl) propanoate ] with the unexpected cis-stereochemistry (11). Irradiation of (4) produces, inter alia, a compound containing the unusual tetracyclo [7.4.0.02,7.04,8] trideca -1(9),10,12-triene skeleton whose structure was determined by n.m.r. spectroscopy.
Complexation of Thallium(I) by 18-Crown-6, Dibenzo-18-crown-6 and Dicyclohexyl-18-crown-6 in Methanol and N,N-Dimethylformamide. Polarographic and MNDO Studies
Authors: Lada E , Filipek S , Kalinowski MK
Published: September 2010

The complexation of thallium(I) by 18-crown-6, dibenzo-18-crown-6 and dicyclohexyl-18-crown-6 (cis-anti-cis isomer) was studied in methanol and N,N- dimethylformamide by a polarographic technique. The equilibrium stability constants were compared with the electron density distributions, calculated by the MNDO method, at the oxygen atoms of the macrocycles.
Structure and Conformations of GABA-Transaminase Inhibitors. IV. Transition State Analogs
Authors: Andrews PR , Gulbis JM , Iskander MN , Mackay MF , Dipaola C , Sadek M
Published: September 2010

Crystal structures of three potential inhibitors [salicylamide derivative C16H15NO4 (5), pyridoxazine C11H16N2O5S (6) and benzoxazone C12H13NO4 (7).H2O] of GABA- transaminase (E.C.2.6.1.19, GABA-T) based on the calculated transition state of GABA-T were determined. The conformational analyses of these structures (non-bonded energies, MNDO,AM1) indicate that they can all fit the transition state in relatively low energy conformations. The crystal structures appear to be close to the calculated minimum energy conformations, except for the salicylamide derivative (5), which features internal hydrogen-bonding. The AM1 parametrization has been used successfully to predict two possible hydrogen-bonded conformations of (5), one of which is found in the crystal structure.