摘要:

AbstractThe kinetics of the gas‐phase pyrolysis of ω‐chlorocarboxylic acids were examined in a seasoned static reaction vessel and in the presence of at least twice the amount of the free radical inhibitor cyclohexene or toluene. In conformity with the available experimental data on rate determination, these reactions proved to be unimolecular and obeyed a first‐order rate law. The presence of the primary chlorine leaving group in Cl(CH2)nCOOH (n= 1–4) showed a change in mechanism from intramolecular displacement of the Cl leaving group by the acidic hydrogen of the COOH to anchimeric assistance of the carbonyl COOH to the CCl bond polarization in the transition state. This mechanistic consideration is nearly the same for the series of 2‐, 3‐, and 4‐chlorobutyric acids. The chlorine atom at the 2‐position of acetic, propionic and butyric acids is dehydrochlorinated through a prevailing reaction path involving a polar five‐membered cyc

ISSN:0894-3230    

DOI:10.1002/poc.610080302

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractKinetic studies were carried out on the thermal epimerization by pyramidal inversion of optically active (S)‐(−)Se‐ and (R)‐(+)Se‐4‐[(‐)‐menthyloxycarbonyl]phenyl(2′,4′,6′‐triisopropylphenyl)selenonium‐N‐toluene‐4″‐sulphonimides (1). The first‐order rate constants for the pyramidal inversion of (S)‐(−)Se‐1 and (R)‐(+)Se‐1 were determined and the activation enthalpies and entropies were calculated. A fairly large difference was found in the activation parameters between optically active (S)‐(−)Se‐1 and (R)‐(+)Se‐1, i.e. a large negative act

ISSN:0894-3230    

DOI:10.1002/poc.610080303

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractUV spectra of 17para‐Y‐substituted styrenes, 8para‐Y‐substituted α‐methylstyrenes and 20para‐Y‐substituted α,β,β‐trifluorostyrenes were measured and correlated against spin‐delocalization substituent constants (σ.) with confide

ISSN:0894-3230    

DOI:10.1002/poc.610080304

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractPhotoelectron spectra oftrans‐bicyclo[4.1.0]hept‐3‐ene and two methyl derivatives, 1–3, andcis‐bicyclo[4.1.0]hept‐3‐ene and three of its derivatives, 4–7, were measured.Ab initiomolecular orbital (MO) and density functional theory (DFT) calculations were performed on these compounds. By combining the results of the experimental and computational trends, it was established that the highest occupied molecular orbitals (HOMOs) of 1–3 are the ‘twist’ bent σ bond at the fusion between the two rings whereas for 4–7 the HOMOs are the π orbital in the six‐membered ring. The DFT ordering is the same as that suggested by the photoelectron spectra whereas at the MO level the HOMO always corresponds to the π orbital. The intensities of the photoelectron spectra were calculated at the DFT level and good qualitative agreeme

ISSN:0894-3230    

DOI:10.1002/poc.610080305

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractCrystalline host compounds consisting of a roof‐shaped dicarboxinide framework and pendant diarylethanol analogous subunits were synthesized and shown to form inclusion complexes with small organic molecules such as alcohols, amines, ketones or polar and apolar organic solvents. Clathrate efficiency and selectivity depend on the particular host structure. The crystal and molecular structures of a free host compound (2a) and inclusion compounds [2a·3‐methylcyclohexanone (1 : 1), 1a·3‐methylcyclopentanone (1 : 1), 1a·2‐methylcyclohexanone (1 : 1), 1b·butyronitrile (1 : 1), 1b·propan‐1‐ol (2 : 1) and 1b·(–)‐fenchone (1 : 1)] were determined by x‐ray diffraction analysis. In all the structures, the hydroxyl group is involved in intramolecular hydrogen bonds and the host and guest molecules are held by lattice forces only. The channels and cavities left in the host matrix are large enough to allow disorder or high thermal displacement parameters of the guest molecules. The local packing coefficients for all gue

ISSN:0894-3230    

DOI:10.1002/poc.610080306

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractSemi‐empirical AM1 theoretical calculations were carried out on the pentaphenylethyl and 9‐trityfluorenyl free radicals, related radicals and their precursor hydrocarbons. Previous reports of the preparation of the former radical have been questioned, although the existence of the second is on secure ground. Based on simple energy considerations, it is concluded that pentaphenylethyl should be as readily prepared. However, the acidity of the precursor hydrocarbon is considerably less than that of 9‐tritylfluorene, and possible radical decomposition via dissociation to triphenylmethyl and diphenylcarbene is calculated to be more facile than the corresponding decomposition of 9‐tritylfluorenyl. A previous postulation of a rapid phenyl equilibration of the pentaphenylethyl radical is shown to be un

ISSN:0894-3230    

DOI:10.1002/poc.610080307

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe reaction between acridine orange hydrochloride [3,6‐bis(dimethylamino)acridine hydrochloride] and potassium bromate in dilute sulphuric acid was studied by monitoring the absorbance change at 492 nm. The reaction exhibited complex kinetic behaviour. In excess bromate the reaction had an induction period with slow depletion of acridine orange (AC) followed by a fast depletion step. The initial reaction step was found to be first order with respect to both AC and bromate and second order with respect to H+. The stoichiometric ratio of AC to bromate was 3 : 2. At the end of the induction period, the redox potential of the reaction mixture has shown a distinct rise, while the Br−concentration dropped sharply. The dual role of bromide ion both as an inhibitor and autocatalyst is discussed. A 16‐step reaction mechanism is proposed and the simulated curves agreed well with the kinetic c

ISSN:0894-3230    

DOI:10.1002/poc.610080308

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe oxidation of 1‐phenyl‐2,2,2‐trifluoroethanol (ROH) with potassium permanganate in 0.2Maqueous sodium hydroxide solution at 25 °C provides 2,2,2‐trifluoroacetophenone as the sole product. The reaction rate constant, which was measured under pseudo‐first order conditions by following the decrease in substrate concentration as a function of time, was found to be substantially smaller than previously reported. The primary kinetic deuterium isotope effect was measured ask 2H/k 2D= 14·7 ± 1·0. A hydrogen‐transfer mechanism involving significant tunnelling is proposed. The oxidation of 1‐phenylethanol under similar reaction conditions yields acetophenone as the initial product. The kinetic deuterium isotope effect was found to b

ISSN:0894-3230    

DOI:10.1002/poc.610080309

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe reaction of bis‐silylated ynamines with different nitrosyl reagents affords products derived from an electrophilic attack at the β‐carbon atom and not the expected alkynyldiazonium s

ISSN:0894-3230    

DOI:10.1002/poc.610080310

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY

ISSN:0894-3230    

DOI:10.1002/poc.610080301

出版商:John Wiley&Sons Ltd.    

年代:1995

数据来源: WILEY