Ring-chain Equilibrium Research Articles

Reactions of carbonyl compounds in basic solutions. Part 10. Methoxide-catalysed cyclisation of methyl 2-acylbenzoates and 8-acyl-1-naphthoates

The detailed mechanism of the methoxide-catalysed rearrangement of both normal and pseudo methyl o-acylbenzoates and 8-acyl-1-naphthoates to form indane-1,3-diones and phenalene-1,3-diones, respectively, has been studied. Rate–acidity function correlations for the reactions in methanolic dimethyl sulphoxide give linear relations. The kinetic isotope effects have been observed with kH/kD equal to 0.7–0.9 and 5–7 for methyl o-acetylbenzoate and normal methyl 8-acetyl-1-naphthoate, respectively. The effect of substituents and ring–chain tautomerism on the rates has been considered. For the o-acylbenzoates the initial state is the ring-chain tautomeric equilibrium mixture and the rate-determining step is the intramolecular attack of the anion of the normal ester. For normal 8-acyl-1-naphthoates the rate-determining step is the ionisation of the normal esters; for the corresponding pseudo esters, the rate-determining step is the isomerisation of the psuedo to the normal ester.

The metathesis reaction of cycloolefins and heterocyclic olefins: Thermodynamics and mechanistic aspects

The metathesis reaction of cycloolefins results in polymers consisting of open chain molecules showing a most probable molecular weight distribution. Beside the polymer residual monomer and/or a homologous series of cyclic oligomers are formed by a “back-biting” reaction. The relation between acyclic polymer and cyclic oligomers can be aiscussed in terms of a ring chain equilibrium. The equilibrium, however, is not established instantaneously; the reaction may be kinetically hindered. The oligoner concentration in the kinetically controlled regime is proportional to x−3/2when the thermodynamic equilibrium is established the oligomer distribution is determined by a ring chain equilibrium. From the Jacobson-Stockmayer plots a characteristic ratio of 5,8 is derived for polyoctenylene and of 13,9 for polynorbornene. The Casey carbene (CO)5W=C(C6H5)2 is more active as catalyst than carbenes of the Fischer type such as (CO)5W=C(OCH3)C6H5; Fischer carbenes are only active with respect to strained olefins. Consequently, in the presence of the latter carbene only polymers are observed; the “back-biting” reaction to yield the cyclic oligomers does not occur. The corresponding chromium carbenes (CO)5Cr=C(R)C6H5 promote the metathesis reaction of vinylethers. Cyclic vinylethers, e.g. 2,3-dihydrofuran and 2,3,4,5-tetrahydrooxepin-2-yl acetate are polymerized in a fully head-to-tail fashion.

New method of synthesizing pyridyl- and quinolylcarbonylarenecarboxylic acids

An original method has been developed for the synthesis of a number of pyridyl- and quinolylcarbonylarenecarboxylic acids by condensing anhydrides of aromatic dicarboxylic acids with picolinic and quinaldic acids. The characteristics of the IR spectra of the compounds synthesized are given, and their ring-chain equilibrium transformations are discussed. It has been shown that the protonation of the nitrogen atom of the heterocycle stabilizes the cyclic form.

Olefin metathesis-distribution of products and carbene complex initiation

The metathesis reactions of cycloolefins results in a ring-chain equilibrium of cyclic oligomers and an acyclic polymer. The distribution of the polymer can be described by a most probable molecular weight distribution. The oligomer distribution differs in the kinetically controlled regime of the reaction from the equilibrium situation. The particular cases of norbornene and norbornadiene are discussed. Carbene complexes may be used as initiators. The more stable the carbene the more strained the cycloolefin has to be in order to be polymerizable. With increasing strain the cis-stereoselectivity is significantly attenuated. (CO)5CRCR′R″ may initiate the metathesis reaction of cyclic and acyclic vinylethers. The reaction proceeds in a structurally uniform manner, i.e. only vinylethers are formed, and yields the equilibrium ratio of cis and trans double bonds.

Comparative study of ring-chain isomeric transitions of 2-cyano-substituted benzamides and benzenesulfamides

The rate constants of cyclization and the constant of ring-chain equilibrium of N-isopropyl-2-cyano-substituted benzamide and benzamide and benzenesulfamide by the methods of PMR and IR spectroscopy, and it was shown that in the transition from 2-cyanobenzamides to 2-cyanobenzenesulfamides a sharp destabilization of the cyclic isomeric form is observed; however, the cyclization of 2-cyanobenzenesulfamides proceeds at a higher rate than the cyclization of 2-cyanobenzamides.

Ring-chain tautomerism and thermo- and photochromism of 3-(1-hydroxy-4-methyl-2-naphthyl)propenal imines

A series of previously undescribed 3-(1-hydroxy-4-methyl-2-naphthyl)propenal imines was synthesized. In the crystalline state all of the imines, except the N-(p-nitrophenyl)imine, have an open o-quinoid structure, whereas in solutions in nonpolar solvents they exist in the cyclic 2H-chromene form. In polar solvents the imines display ring-chain tautomeric equilibrium of the 2H-chromene and o-quinoid forms, the relative percentages of which are determined by the character of the substituent in the amino component of the molecule and by the polarity of the solvent. The N-(p-nitrophenyl)imine has-the 2H-chromene structure in the solid phase and in solvents.

Synthesis and thermal stability of carborane‐containing phosphazenes

AbstractCarborane‐substituted polyphosphazenes were prepared by the thermal polymerization of phenyl‐carboranyl pentachlorocyclotriphosphazene. Successive isothermal vacuum pyrolyses were conducted on the polymer and examined for structural changes by infrared spectroscopy. The degradation products were ascertained by gas chromatography‐mass spectrometric analysis. It was found that the presence of the carborane group improves the thermal stability of the polymer by retarding the ring‐chain equilibrium processes of decomposition.

ChemInform Abstract: STRUCTURE AND RING‐CHAIN TAUTOMERISM OF 3‐(1‐HYDROXY‐4‐BROMO‐2‐NAPHTHYL)PROPENAL

AbstractDer aus dem 4‐Brom‐a‐naphthol (I) durch Umsetzung mit Dichlormethylbutylether (II) in Gegenwart von Titantetrachlorid hergestellte Naphthaldehyd (III) wird über das Acetal (IV) mit Vinylbutylether (V) zum Propenal (VI) kondensiert.

Structure and ring-chain tautomerism of 3-(1-hydroxy-4-bromo-2-naphthyl)propenal

The previously undescribed 3-(1-hydroxy-4-bromo-2-naphthyl)propenal was synthesized. This aldehyde exists primarily in the form of the cyclic 2H-chromene tautomer in the crystalline state, in solutions in nonpolar solvents, and in acetonitrile, ethanol, and acetone. Ring-chain tautomeric equilibrium between the 2H-chromene and quinoid structures is observed in dimethyl sulfoxide.

ChemInform Abstract: STRUCTURE AND RING‐CHAIN TAUTOMERISM OF 2‐HYDROXY‐5‐METHYL‐3,4‐BENZOCINNAMALDEHYDE

AbstractAus dem Naphthol (I) wird durch Formylierung, O‐Acetylierung und Acetalisierung das Acetal (VI) hergestellt und dieses durch Kondensation mit Divinylether (VII) in die Benzozimtaldehyde (VIII) und (IX) umgewandelt.

Structure and ring-chain tautomerism of 2-hydroxy-5-methyl-3,4-benzocinnamaldehyde

The previously undescribed 2-hydroxy-5-methyl-3,4-benzocinnamaldehyde was synthesized. A cyclic 2-hydroxy-2H-chromene structure in the crystalline state and in nonpolar solvents was established for it by IR, UV, and PMR spectroscopy. It is shown that transition to a polar solvent leads to the establishment of a tautomeric ring-chain equilibrium, the position of which is determined by the type of solvent.

Equilibrium in the system polycaproamide-caprolactam-water below the melting point of the polymer

It is shown that, from the thermodynamic point of view, the condensation of the macromolecules' end groups and the polyaddition of caprolactam, both occurring in the solid polymer's amorphous phase at 443–483 K are similar to the corresponding reactions in the polymer melt and the temperature dependence of the constants that characterize the conditions of the amide equilibrium and the ring-chain equilibrium are described by the equation log K 2 = 1658·3/ T − 0·4575, log K 3 = 896·9/ T − 1·532.

A Direct Photoelectron Spectroscopy Study of the 2-Azidopyridine Pyrolysis PES, 2-azidopyridine, thermic degradation, MNDO calculations

Abstract In a previous paper1 evidence was obtained by means of photoelectron spectroscopy (Hel) for the existence of a ring-chain equilibrium in the case of tetrazolo [1,5-a] pyridine I.

The metathesis reaction — a route to the synthesis of elastomeric polymers and a scientific challenge

AbstractThe metathesis reaction of olefins is generally assumed to proceed via transition metal carbenes and metalla cyclobutane derivatives as key intermediates. Besides the Phillips trisolefin process the reaction has become technically relevant for the synthesis of special polymers such as polynorbornene. Of scientific interest is the mechanism of the reaction. The particular feature of the metathesis of cycloolefins is the formation of a ring chain equilibrium from which not only cyclic oligomers can be isolated and investigated; moreover, the equilibrium concentration of the cyclic oligomers yields valuable conformational information on the respective chain.

Ring-chain tautomerism of substituted hydrazones. 17. Alkyl-substituted perhydro-1,3,4-thiadiazines

It was demonstrated by PMR spectroscopy that alkylidene derivatives of vic-(Nalkylhydrazino) thiols in solutions exist exclusively in the cyclic form, i.e., as perhydro-1,3,4-thiadiazines. Only pinacolone derivatives undergo reversible isomerization to the corresponding hydrazones. The thermodynamic parameters of the ring-chain equilibria were determined. The static stereochemistry and the dynamics of the conformational transitions of perhydro-1,3,4-thiadiazines are discussed.

Heat capacity and other thermodynamic properties of linear macromolecules. I. Selenium

The heat capacity of selenium from 0 K to 1000 K is reviewed using measurements on 20 samples reported in the literature. A set of recommended data for trigonal, monoclinic, glassy, and molten selenium is derived. Ring-chain equilibrium parameters are critically evaluated. Entropy, enthalpy, and Gibbs energy functions are calculated. Selenium is a model compound for a monoatomic, linear macromolecule. This paper is first in a series which will ultimately cover all heat capacity measurements on linear macromolecules.

Photo- and thermochromic 2-amino-2H-chromenes

A number of N-aryl- and N-alkylimines of 2-hydroxy-5,6-benzocinnamaldehyde were synthesized. The cyclic 2-amino-2H-chromene structure in nonpolar solvents was established for them by IR, UV, and PMR spectroscopy. It is shown that the transition to polar solvents leads to the establishment of a tautomeric ring-chain equilibrium. The equilibrium thermal transformations and phototransformations of some N-aryl- and N-alkylimines were studied.

Kinetics and thermodynamic aspects of the metathesis reaction of cycloolefins considering particularly the molecular weight distribution of the products

The rate of polymerization of cycloolefins is to a very high degree dependent on the catalyst used and so is the induction period. The order of the reaction with respect to monomer and catalyst concentration as well as activation energy and entropy have been determined. Product distribution and configuration of the double bonds initially are kinetically controlled. The thermodynamics of the polymerization of cycloolefins are discussed in terms of ring size. The reaction products generally consist of cyclic oligomers and an acyclic polymer. As equilibrium is approached, above a certain minimum initial monomer concentration (cut-off point) an invariable concentration of oligomers is obtained. With increasing monomer concentration an increasing amount of polymer is formed. The concentration of cyclics is discussed in terms of a ring—chain equilibrium.

Ring-chain equilibrium in the anionic polymerization of δ-valerolactone

The anionic polymerization of δ-valerolactone in tetrahydrofuran with lithium tert-butoxide was found to give a living ring-chain equilibrium system, in which the cyclic oligomers are produced by back-biting degradation from the initially formed linear polymers. The molar cyclization equilibrium constant for the trimer through hexamer decreased in proportion to −2.5 power of the ring size, in accord with the Jacobson-Stockmayer theory.

The ring-chain equilibrium in derivatives of 5-nitro-1, 2, 3, 4-tetrahydropyrimidine in trifluoroacetic acid

Abstract 1H NMR spectra of derivatives of 5-nitro-1,2,3,4-tetrahydropyrimidine were examined in trifluoroacetic acid solution. It was found that the compounds, unsubstituted in position 2, preserve their ring structure, whereas 2-alkyl- and 2-aryl derivatives are subjected to ring opening.