bluuebunny/crossref_metadata_2025_split huggingface dataset:
Supramolecular effects on photochromism—properties of crown ether‐modified dihydroindolizines
Authors: Dürr H. , Thome A. , Kranz C. , Kilburg H. , Bossmann S. , Braun B. , Janzen K.‐P. , Blasius E. 
Published: January 2005

AbstractPhotochromic molecules such as dihydroindolizines (DHI) containing crown ether units can be ‘tuned’, as far as their properties are concerned, by supramolecular ion binding. Inclusion of the ion in the crown ether cavity yields a new supramolecular species. This species shows special properties of the excited state after guest addition: (a) bathochromic shifts of the photochromic crown ethers and also hyperchromic effects in the UV spectra; (b) fluorescence intensity of one of the photochromic crown ethers is either increased (crown excitation) or decreased (DHI excitation) after addition of alkali metal ions; and (c) in the ground state a large change in reaction rate for the reaction 1,5‐electrocyclization betaine (coloured form) to dihydroindolizine is observed in the supramolecular complexes.
Metal ion‐promoted hydrolysis of uridine 2′, 3′ ‐ cyclic monophosphate: Effect of metal chelates and uncomplexed aquo ions
Authors: Kuusela Satu , Lönnberg Harri 
Published: January 2005

AbstractThe effect of a wide variety of metal ious and metal ion complexes on the hydrolysis of uridine 2′,3′‐cyclic monophosphate was studied over the pH range 4.5–8.0. The greatest rate accelerations observed were 107–108‐fold. The kinetic data obtained are interpreted in terms of a mechanism involving arapid monodentate binding of the metal ion to the monoanionic phosphodiester and a subsequent intracomplex participation of the metal‐bound hydroxo ligand, either as a nucleophile attacking the tetracoordinated phosphorus or as a base facilitating an intermolecular attack of a water molecule. No effect on the product distribution between uridine 2′‐ and 3′‐monophosphates was observed.
Alkaline hydrolysis of substituted benzyl substituted benzoates
Authors: Yoh Soo‐dong , Cheong Duk‐young , Tsuno Yuho 
Published: January 2005

AbstractThe kinetics and mechanism of the alkaline hydrolysis of both acyl‐ and aryl‐substituted benzyl benzoates were studied in 80% (v/v) aqueous acetone at 20, 34, and 40 °C. Each of the substituted benzyl alcohols generated an independent σ–ρ plot which was correlated well with the Hammett equation (R = 0·996−0·999). The values of ρ for the acyl moiety showed no tendency either to increase or to decrease with the intrinsic reactivity of the parent benzyl alcohol and were all within ±0·098 of the mean of 2·236. However, the Hammett ρ values for the leaving groups decreased from H to p‐NO2 substituents of the acyl part, in which the values were smaller than those of acyl moieties and fairly accurately obeyed the σ0 values rather than the σ values. The rate data for benzyl‐substituted benzoates were correlated by the Yukawa–Tsuno equation, log k/k0 = 1·72(σ0 + 0·49Δ) − 0·020, R = 0·996. The results suggested that the alkaline hydrolysis of benzyl benzoates showed a greater sensitivity to acyl than aryl activation, and the rates and activation parameters were largely determined by the addition step. The results are attributed to the preferential partitioning of an unstable tetrahedral intermediate to the products.
Acidity constants of benzamide and some Ortho‐substituted derivatives
Authors: García Begoña , Casado Rosa M. , Castillo Julio , Ibeas Saturnino , Domingo Inmaculada , Leal José M. 
Published: January 2005

AbstractAcidity constants of benzamide and seven ortho‐substituted derivatives were determined. Except for o‐nitrobenzamide, all the amides exhibit medium effects. The data were treated by vector analysis. o‐Aminobenzamide displays two protonation equilibria. The second acidity constant was determined by vector analysis and by the excess acidity function, since the acid strength provided by perchloric acid is insufficient for complete protonation. Different acidity functions and the ortho substituent effect on ionization of the amide group are compared.
Determination of the existence, value and uncertainty of the compensation or isokinetic temperature
Authors: Alper Joseph S. , Gelb Robert I. 
Published: January 2005

AbstractThe demonstration of the existence of a compensation effect, the linear dependence of the enthalphy on the entropy for a series of chemical reactions, is often complicated by an apparent linear dependence arising solely from experimental errors. A non‐linear least squares method has been developed for establishing the existence or non‐existence of a compensation effect and for determining the value of the compensation temperature if the effect exists. The uncertainty in the value of the compensation temperature can be determined by means of a Monte Carlo procedure. If a compensation effect does not exist, three cases can be distinguished: (1) the relationship between the enthalpy and entropy is linear, but the compensation temperature is 0 K; (2) the various reactions cannot be distinguished from each other because of experimental errors; and (3) the reactions do differ, but the relationship (if one exists) between the enthalpy and entropy is not linear. The method is illustrated using both hypothetical and experimental examples.
Evidence for the presence of the CH–π‐interacted ap‐conformers of benzyl formates
Authors: Suezawa Hiroko , Mori Akiyoshi , Sato Masayuki , Ehama Ritsuko , Akai Ikuo , Sakakibara Kazushisa , Hirota Minoru , Nishio Motohiro , Kodama Yoshio 
Published: January 2005

AbstractIn order to examine the preferred conformations of benzyl, 1‐phenylethyl and cumyl formates, lanthanoid‐induced shifts (LIS) of 1H and 13C NMR and difference NOE spectra of these esters were measured. The measurements showed that a folded conformer capable of forming intramolecular CH–π interaction are predominant with all three series of formate esters. The LIS and other experiments suggested the coexistence of considerable amounts of extended conformers, however. As the ester group is enforced to take supposedly unfavourable ap‐conformation in the CH–π contiguous folded conformer, the predominance of the conformer was a surprise and needed explanation. The NOE experiments on a series of para‐substituted benzyl formates, XC6H4CH2OCHO (X = CH3O, CH3, H, Cl, NO2), showed that the enhancement of aromatic proton signals (ortho and meta) induced by the irradiation of formyl proton increases gradually as the substituent becomes more electron donating, whereas the enhancement of benzylic (α) proton signal remains constant irrespective of the nature of the substituent. This can be explained by assuming that the CH–π contiguous folded conformer is in equilibrium with the extended conformer. The trend of the substituent effect supports the hydrogen bond‐like nature of the CH–π interaction. A similar trend was also observed with substituted 1‐phenylethyl formates. Hence the unexpected stability of the ap‐conformer of benzyl formates could be ascribed to the stabilization due to the CH–π interaction.
Structural study on 1‐phenyl‐ and 1‐(2‐naphthyl)‐8‐tropylionaphthalene hexafluoroantimonates
Authors: Tsuji Ryotaro , Komatsu Koichi , Takeuchi Ken'ichi , Shiro Motoo , Cohen Shmuel , Rabinovitz Mordecal 
Published: January 2005

AbstractThe molecular structures of 1‐phenyl‐ (5) and 1‐(2‐naphthyl)‐8‐tropylionaphthalene (6) hexafluoroantimonates were determined by x‐ray crystallography and compared with those of 1,8‐diphenylnaphthalene and related compounds. In these compounds, the two aromatic substituents face each other in a nearly parallel conformation with a splayed‐out arrangement. In the cations 5 and 6, the distance between the facing rings is appreciably shorter than that of other 1,8‐diarylnaphthalenes, suggesting the presence of some attractive force. This attraction is ascribed to an intramolecular charge‐transfer interaction, and seems to bring about a slight inward bending of the 2‐naphthyl substituent in the cation 6. AM1 calculations were carried out for these cations and the results are discussed in comparison with the results of x‐ray crystallography.
Photoreaction of 2‐benzoylcyclohexanones on a silica gel surface: Deviation from their solution photochemistry
Authors: Hasegawa Tadashi , Imada Manabu , Yoshioka Michikazu 
Published: January 2005

AbstractOn irradiation on a dry silica gel surface, 2‐benzoylcyclohexanones which have the lowest n, π* state and are devoid of methyl substituents on their cyclohexanone rings, undergo an oxidative cleavage to give adipic acid and subsituted benzoic acid along with the Norrish Type II product. Irradiation of 2‐chlorocylohexanone and cyclohexane‐1,2‐dione on silica gel also gives adipic acid. The cyclohexanonyl radical on the surface, which is produced from the α‐cleavage of the 2‐benzoyl group of the 2‐benzoylcyclohexanones or the cleavage of the CCl bond of 2‐chlorocyclohexanone, is suggested as the precursor of adipic acid; the radical is probably converted into cyclohexane‐1,2‐dione, which undergoes a secondary photoreaction to give adipic acid on the surface.
Using theoretical descriptors in structure–activity relationships: Solubility in supercritical CO2
Authors: Famini George R. , Wilson Leland Y. 
Published: January 2005

AbstractThe use of quantitative structure–activity relationships (QSAR) in correlating biological phenomena to chemical structure, and the use of linear free energy relationships (LFER) and linear solvation energy relationships (LSER) for correlating physical phenomena are becoming standard occurrences. In this work the empirical LSER solvatochromic descriptors were replaced with a computationally derived set to aid in a priori property prediction. This paper deals with the application of this descriptor set to correlating the solubilities of 22 compounds in super critical CO2. A reasonable correlation, consistent with previous correlations by other researchers, was found.
Nucleophilic catalysis in deoxymercuration: The beta effect of mercury
Authors: Lambert Joseph B. , Emblidge Robert W. 
Published: January 2005

AbstractDeoxymercuration was examined in the antiperiplanar stereochemistry of trans‐2‐acetoxycyclohexylmercury(II) acetate (6). The presence of the mercury group accelerates the departure of the beta leaving group by a factor of about 1010. This beta effect is larger than that of silicon and comparable to that of germanium. In contrast to these latter cases, the rate for 6 was found to increase with the nucleophilicity of the solvent. It is concluded that a molecule of solvent is coordinated with mercury in the transition state. This nucleophilic assistance raises the polarizability and nucleophilicity of the mercury group, enhancing its ability to stabilize the developing positive charge or to form a bridged intermediate.
Stereochemical structures of (8,8‐ethylenedioxy‐2‐oxo‐)‐ and (8,8‐ethylenedioxy‐2‐hydroxy‐)‐6‐phenylsulphonylbicyclo[3·3·0]octanes
Authors: Tinant Bernard , Declercq Jean Paul , Wynants Chantal , Demillequand Marc 
Published: January 2005

AbstractCyclopentannulation of 4‐tert‐butyldimethylsilyloxy‐2‐cyclopenten‐1‐one from a β‐metallated dioxolane‐type orthoester affords 4‐tert‐butyldimethylsilyloxy‐8,8‐ethylenedioxy‐6‐phenylsuiphonyl‐2‐oxobicyclo [3·3·0] octanes as a mixture of two diastereoisomers. Their stereochemical structures were established by NMR and x‐ray analysis. The minor product possesses a cis ring fusion, the sulphonyl and the tert‐butyldimethylsilyloxy groups being endo and exo, respectively. The major isomer also has a cis ring fusion but an exo position for both dimethylsilyloxy and sulphonyl groups. Both cyclopentannulation products result from an anti addition with respect to the 4‐tert‐butyldimethylsilyloxy group on the enone.
Cationic and anionic halochromism
Authors: Zanotto Sandra P. , Scremin Marivania , Machado Clodoaldo , Rezende Marcos Caroli 
Published: January 2005

AbstractThe spectral changes of organic solutions of N,N,N′,N′‐tetramethylenediaminoacetylacetonatocopper(II) perchlorate and a merocyanine dye in the presence of NaI or LiClO4 provide examples of anionic and cationic halochromism, respectively. The observed changes are interpreted as arising from all possible interactions in the three‐component system of the dye, the salt and the solvent.
Nucleophilic participation in the solvolyses of 2‐aryl‐2‐halopropanes and the previously claimed advantage of using YBnX scales
Authors: Kevill Dennis N. , D'Souza Malcolm J. 
Published: January 2005

AbstractContrary to a recent report, the specific rates of solvolyses of five 2‐aryl‐2‐chloropropanes give only marginally (not significantly) better correlations with use of the YBnCl scale rather than the YCl scale. With the use of the extended (two‐term) Grunwald–Winstein equation, some evidence for a weak nucleophilic solvation is obtained, but at a low confidence level. The specific rates of 2‐bromo‐2(p‐trifluoromethylphenyl)propane solvolysis are significantly better correlated using YBr (rather than YBnBr) values and, indeed, the use of NT values in conjunction with YBr values leads to an l value of 0·17 ± 0·06 and evidence for a weak nucleophilic participation at a 98·7% confidence level.
Potentiometric evaluation of the ion‐selective characteristics of 1,4‐bridged cubyl diester crown ethers
Authors: Moriarty Robert M. , Rao M. Suresh Chander , Tuladhar Sudersan M. , Gilardi Richard , D'Silva Claudius , Williams Gwyn 
Published: January 2005

AbstractCubane diester crown ethers were tested as ion‐selective electrodes in poly(vinyl chloride) (PVC) membranes. The four ionophores studied proved to be good K+ neutral carriers, showing Nernstian and near‐Nernstian responses to this ion, in the range 10−4–10−1 M. The fixed interferences method was used to determine relative selectivity coefficients for all the electrodes. The highest selectivity for potassium relative to sodium, lithium, calcium and magnesium ions using potassium tetrakis(p‐chlorophenyl)borate (KTpClPB) as a resistance modifier and NPOE as a plasticizer was obtained with the 1,4‐cubyl diester‐25‐crown‐7 ether ionophore. The effects of KTpCIPB on membrane selectivity were assessed; its removal was found to increase the selectivity of the four ionophores for potassium relative to cesium, sodium, calcium and magnesium ions with minimal effects on lithium and ammonium ions. The compounds tested exhibited a fast Nernstian response to changes in K+ concentration which was stable to within <100 μV h−1.
Orbital‐controlled reactions catalysed by zeolites: Electrophilic alkylation of aromatics
Authors: Corma A. , Zicovich‐Wilson C. , Viruela P. 
Published: January 2005

AbstractThe role of orbital control in product selectivity during electrophilic aromatic alkylation catalysed by zeolites was studied both theoretically and experimentally. In order to discuss this, the alkylation of toluene and m‐xylene by methanol was carried out on a series of large‐pore zeolites (HY). The changes in the para to ortho ratio observed on changing the framework Si/Al ratio of the zeolites were related to ab initio molecular orbital calculations of the LUMO energy of structurally alike model clusters but containing different tetrahedral cations around the active site. The observed correlation is discussed in terms of the HSAB principle by taking into account the influence of the catalyst composition on the reactivity of the electrophilic reagent.
An E ⇌ Z isomerization of an electrophilic vinyl azide by 15N. A probe for internal rotation processes in the carbanionic intermediate of nucleophilic vinylic substitution
Authors: Jonas Jaroslav , Mazal Ctibor , Rappoport Zvi 
Published: January 2005

AbstractThe label incorporation and Z → E isomerization in the reaction of 3‐azidomethylenedihydro‐(3H)‐furan‐2‐one with Na15NN2 in 1:1 water–acetone were measured as a probe for internal clockwise vs anticlockwise rotation in the intermediate carbanion.
Topological analysis of electronic charge densities as a tool to study protonation effects on thiocarbonyl compounds
Authors: Yáñez O. MÓ M. , Esseffar M. , Abboud J.‐L. M. 
Published: January 2005

AbstractThe substituent effects on the intrinsic basicity of a wide variety of thiocarbonyl compounds were investigated by means of a topological analysis of the electronic charge densities and their Laplacians for the neutral and the protonated species, and also by means of their harmonic vibrational frequencies. For the sake of comparison, a similar analysis was carried out for a reduced set of carbonyl compounds with similar substituents. The results show that the behaviour of the thiocarbonyl group with regard to the protonation process is similar to that predicted for the carbonyl group, in the sense that both groups are not much affected by protonation. The charge transferred to the proton results basically in a polarization and, in some cases, in a depopulation of the bonds in which the thiocarbonyl carbon atom participates. Accordingly, the intrinsic basicities of these kinds of compounds depend strongly on the ability of the substituents to be polarized. This conclusion seems to be ratified also by the shiftings undergone by the C=S stretching frequencies on protonation.
Linear solvation energy relationships between electrolyte pK values and solvent properties for several 2‐methylpropan‐2‐Ol–cosolvent mixtures
Authors: Bosch Elisabeth , Rived Fernando , Rosés Martí 
Published: January 2005

AbstractThe dissociation pK values of picric acid, tetrabutylammonium picrate, bromide and hydroxide and tetramethylammonium hydroxide in some 2‐methylpropan‐2‐ol–cosolvent mixtures were determined and correlated with the Taft and Kamlet solvatochromic parameters π*, δ, α and β. The results show the most important solvent properties that affect electrolyte dissociation are polarity, polarizability and hydrogen bond acidity. These results were confirmed by analysis of published literature data.
Interrelations Of the energetics of amides and alkenes: Enthalpies of formation of N,N‐dimethyl derivatives of pivalamide, 1‐adamantylcarboxamide and benzamide, and of styrene and its α‐, trans‐β‐ and β,β‐methylated derivatives
Authors: Abboud José‐Luis M. , Jiménez Pilar , Roux M. Victoria , Turrión Concepcióon , Lopez‐Mardomingo Carmen , Podosenin Andrew , Rogers Donald W. , Liebman Joel F. 
Published: January 2005

AbstractThe enthalpies of formation of the condensed phase and gaseous N,N‐dimethyl derivatives of pivalamide, 1‐adamantylcarboxamide and benzamide were determined by combustion calorimetry and the associated enthalpies of vaporization and sublimation. The enthalpies of formation of styrene and its α‐, trans‐β‐ and β,β‐methylated derivatives were determined from measurements of their enthalpies of hydrogenation in dilute hydrocarbon solution. Strain and resonance effects of amides and alkenes are discussed in terms of the exo‐/endothermicity of the following reactions:

equation image

and in terms of the difference of enthalpies of formation of the isomeric (Z)‐ and E‐RCHCHCH3.
Photoisomerization of 3‐benzoylacrylates on a silica gel surface: Effect of reaction environment on selectivity
Authors: Hasegawa Tadashi , Yamazaki Yuko , Yoshioka Michikazu 
Published: January 2005

AbstractOn irradiation on a dry silica gel surface, 2‐(N, N‐dialkylamino)ethyl 3‐benzoylacrylates undergo selective E‐Z isomerization. Competing processes, such as remote‐hydrogen abstraction via a charge‐transfer state, with the photoisomerization in solution are completely suppressed on the surface. The yield of the Z ‐ from the E‐ isomer increases with increase in the coverage of the E‐isomer on the surface, reaching a limiting value. Thermal isomerization of the Z‐ to the E‐ isomer occurs easily on the silica gels surface when the alkyl group on the nitrogen atom is small. Benzoylacrylates without any amino group also undergo selective photoisomerization.
Living polymerization of methacrylic esters with aluminium porphyrin initiators. Axial ligand exchange activities of alkyl‐ and enolate‐aluminium porphyrins in relation to the polymerization Mechanism
Authors: Aida Takuzo , Sugimoto Hiroshi , Kuroki Masakatsu , Inoue Shohei 
Published: January 2005

AbstractPolymerization of methacrylic esters such as benzyl methacrylate using as initiator an‐equimolar mixture of methylaluminium 5,10,15,20‐tetraphenylporphine [(TPP)AlMe] and 2,7,12,17‐tetramethyl‐3,8,13,18‐tetramethylporphine [(EtioP)AlMe] proceeded from both initiators, affording a unimodal polymer of narrow molecular weight distribution, although the reactivities of (TPP)AlMe and (EtioP)AlMe are very different from each other. 1H NMR studies on a mixture of two different (porphinato)aluminium enolates, the growing species, and a mixture of a (porphinato)aluminium enolate and an alcoholate, in the absence and presence of methyl methacrylate (MMA or MMA‐d8), indicated an acyclic transition state polymerization mechanism by the participation of two aluminium porphyrin molecules, where the growing species always exchange their enolate ligands whenever it grows.
‘Living’ and controlled radical polymerization
Authors: Matyjaszewski Krzysztof , Gaynor Scott , Greszta Dorota , Mardare Daniela , Shigemoto Takeo 
Published: January 2005

AbstractRadical polymerizations cannot truly be ‘living’ because of the inevitable termination between growing radicals. However, relatively good control of molecular weights, polydispersities and terminal functionalities can be achieved by using either unimolecular or bimolecular exchange between growing radicals and dormant chains. The dormant chains can be in the form of either covalent species or organometallic compounds. Some systems based on alkoxyamines, organochromium compounds, organoaluminum compounds and alkyl iodides were studied and are discussed in detail.
Oscillations of electrical potential differences across the interface in phase‐transfer catalytic systems
Authors: Srivastava R. C. , Agarwala V. , Upadhyay S. , Varghese V. A. , Sahney R. 
Published: January 2005

AbstractOscillations of electrical potential differences across the liquid–liquid interface in phase‐transfer catalyst systems are reported. The occurrence of the oscillations is consistent with the Starks' shuttling mechanism.
Tributylammonium cyanamidate BU3N+–N−–C≡N: A ‘super‐basic’ nitrile group more basic, on the hydrogen‐bond basicity scale, than any amine or pyridine
Authors: Chardin Aurélie , Berthelot Michel , Laurence Christian , Morris David G. 
Published: January 2005

AbstractAn IR spectroscopic study of the hydrogen bonding of Bu3N+N−C≡N with 4‐fluorophenol showed that the site of complexation is the nitrogen of the nitrile function. THe formation constant of the 1:1 complex in CCl4 indicates that this cyanamidate is a stronger hydrogen‐bond base than is any nitrile, amine or pyridine. The Bu3N+–N− group increases the basicity of the nitrile group very efficiently because of the conjugation of two lone pairs on the anionic nitrogen with the π systems of the cyano group. This conjugation is also exemplified by the very low ν(C≡N) wavenumber (2104 cm−1).
Substitutent effects in monosubstituted benzenes: Semi‐empirical SCF studies of the Hammett constants
Authors: Monaco Regina R. , Gardiner William C. 
Published: January 2005

AbstractSemi‐empirical SCF calculations using the AM1 Hamiltonian were shown to account for the Hammett σ constants and other properties of a representative series of 22 monosubstituted benzenes in terms of the atomic charges at the ipso, ortho, meta and para positions. The trends of the correlations with experimental σ constants were found to follow the normal expectations of physical organic chemistry. Additional support for the AM1 charge distributions was obtained in correlations with the 13C chemical shifts of 12 of the test molecules. On the other hand, no correlations were found between σ constants and computed force constants for bending peripheral H atoms out of the plane of the aromatic ring, supporting the view that Hammett σ constants reffect charge distributions and not secondary effects expressed in the stiffness of bonds.