The mass spectra of carboxylic acids—V: Carboxyl-carboxyl interaction in the fragmentation of some cycloalkene-1,2-dicarboxylic acids

The fragmentation mechanisms of the six isomeric cyclohexene-1,2-dicarboxylic acids are discussed. Only the 1-cyclohexene acid, by virtue of the major sequential losses of H₂O and CO₂ from the molecular ion, is readily distinguishable from its isomers, all of whose mass spectra are closely similar. In contrast to cis and trans cyclohexane-1,2-dicarboxylic acids, whose mass spectra were markedly different, the cis and trans cyclohexene-1,2-dicarboxylic acids fragment in a similar fashion. The mass spectra of 1-cyclopentene-1,2-dicarboxylic acid and 1-cyclobutene-1,2-dicarboxylic acid also exhibit a strong carboxyl-carboxyl interaction; the fragmentation behaviour of the 1-cyclopenteneacid is, however, more complex than that of the 1-cyclohexene and 1-cyclobutene acids.     

Stereochemistry of Macrocyclization of cis-4-Cyclohexene-1,2-dicarboxylic Acid with Dihalogen Derivatives

Stereochemistry of [2+2]- and [1+1]-macrocylization of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,2-dibromoethane, 1,3-dichloro-2-propanol, and 1,5-dichloro-3-oxapentane was studied. The reaction of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,2-dibromoethane according to the [2+2]-cyclization scheme gave a mixture of stereoisomeric macroheterocycles with cis,syn,cis- and cis,anti,cis-junction of the polyether and cyclohexene rings. In the reaction of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,5-dichloro-3-oxapentane, a mixture of crown compounds with cis,anti,cis- and cis-junction of the polyether and cyclohexene rings was obtained. The structure of the products was established on the basis of their chemical transformations and spectral data.     

The dissimilarity between the electron-impact and photochemical or thermal behaviour of some methyl cyclobut-3-ene-1,2-dicarboxylates and muconates

Comparison of the mass spectral behaviour of the dimethyl esters of the epimeric (cis- and trans-) cyclobut-3-ene-1,2-dicarboxylic acids and the isomeric muconates (cis, cis-, cis, trans- and trans, trans-) and some substituted analogues shows that no correlation exists between the electron-impact-induced fragmentation and the predicted photochemical or thermal transformations in these systems. The comparison involved fragmentation patterns (supported by deuterium labelling), metastable transitions, and also kinetic energy release in the field free region.     

Stereochemical applications of mass spectrometry. II—Chemical ionization mass spectra of isomeric dicarboxylic acids and derivatives

The H₂ and CH₄, chemical ionization mass spectra of the cis dicarboxylic acids, maleic and citraconic acid, show much more extensive loss of H₂O from [MH]⁺ than the trans isomers, fumaric acid and mesaconic acid. Similarly, esters of maleic acid show a much more facile loss of ROH (R=alkyl or phenyl) from [MH]⁺ than do esters of fumaric acid. Similar differences are observed in the chemical ionization mass spectra of the isomeric phthalic and isophthalic acids and derivatives, where the ortho isomers show more extensive fragmentation of [MH]⁺ than the meta isomers. The facile fragmentation of [MH]⁺ for the cis and ortho isomers is attributed to ROH elimination involving interaction between the two carboxylate functions and forming the stable cyclic anhydride structure for the fragment ion. By contrast ROH elimination from [MH]⁺ for the trans and metu isomers requires a symmetry-forbidden [1,3]-H migration in the carboxyl protonated species and cannot lead to the cyclic anhydride structure. The chemical ionization mass spectra of cis and trans cyclohexane-1,2-dicarboxylic acids are essentially identical and show extensive fragmentation of the [IMH]⁺ ion. Experiments using deuterium labelling show extensive carboxyl group interactions for both isomers. The chemical ionization mass spectra of maleanilic and phthalanilic acids and of the related anhydrides and imides also are reported, as are the electron impact mass spectra of diphenyl maleate, diphenyl fumarate, diphenyl phthalate, maleanilic acid and phthalanilic acid.     

1H-NMR-Spektroskopische Untersuchungen zur Konformation von Cyclohexandicarbonsäure-(1,2)-anhydriden

¹H NMR chemical shifts of 18 methyl substituted cyclohexane-1,2-dicarboxylic anhydrides were determined. In compounds with asymmetric substitution vicinal coupling constants were measured. In the series of trans-anhydrides it can be deduced from the NMR data, that the 6-membered ring has a chair-like conformation. Additionally, in the series of the cis-anhydrides a twisted chair conformation is favoured for the most part.     

The mass spectra of carboxylic acids—I: Fragmentation mechanisms in maleic and fumaric acids and related compounds

The mass spectra of maleic acid, maleic acid-2,3-d, fumaric acid and fumaric acid-2,3-d have been examined and fragmentation mechanisms are proposed for these compounds. The molecular ion of the cis-acid fragments via H atom transfer from one carboxyl group to the other followed by loss of CO₂. The trans acid does not fragment significantly by this route and the former effect may be characteristic of molecules containing two carboxyl groups cis-oriented to each other. This hypothesis was successfully tested by examining the mass spectra of citraconic, itaconic and phthalic acids. Itaconic and mesaconic acids show some of the fragmentation characteristics of fumaric acid.     

Pyranosides with 2,3‐trans Carbamate Groups: Exocyclic or Endocyclic Cleavage Reaction?

Pyranosides with 2,3‐trans carbamate groups exhibit high 1,2‐cis selectivity in glycosylation reactions. Using glycosyl donors with N‐benzyl 2,3‐trans carbamate groups, an anti‐Helicobacter pylori oligosaccharide was synthesized in an efficient manner. Moreover, pyranosides with 2,3‐trans carbamate groups readily undergo anomerization from the β to the α configuration under mild acidic conditions via endocyclic cleavage. Acyclic cations generated during the endocyclic cleavage reaction were captured using reduction and intramolecular Friedel–Crafts reaction. By exploiting this anomerization, multiply aligned 1,2‐trans glycosyl bonds can be transformed to 1,2‐cis glycosyl bonds in a single operation.     

Thermal degradation of copolymers of styrene with dicarboxylic acids - II: Copolymers obtained by radical copolymerisation of styrene with maleic acid or fumaric acid

Thermal degradation processes in copolymers of styrene with two stereoisomers of 1,2-ethylenedicarboxylic acids (i.e. maleic acid (the cis-isomer) and fumaric acid (the trans-isomer)) have been studied by mass spectrometry, FTIR and TG measurements. The influence of the chemical composition on thermal degradation of copolymers with acid by non-isothermal thermogravimetric analysis (TG) was also studied. The stereo-configuration of carboxyl groups in copolymers was analysed by potentiometric titration. It was found that copolymers degrade in two main complex stages. The initial step in the decomposition involves the formation of cyclic five-membered anhydrides. The presence of trans configuration of carboxyl groups hinders the formation of cyclic anhydrides and shifts the decomposition to higher temperatures, making decarboxylation competitive. At higher temperatures anhydride decomposition takes place and finally the degradation of main chains occurs.     

Reactivities of cis- and trans-3-substituted acrylic acids on copolymerization with acrylamide

Several pairs of cis- and trans-3-substituted acrylic acids (3SAA) were copolymerized with acrylamide in order to determine the major factors affecting the relative reactivities of geometrical isomers of 1,2-disubstituted ethylenes (1,2-DE). The results were that the relative reactivity of cis isomer is larger than that of trans isomer when one substituent is electron-withdrawing and the other is electron-donating. The trans isomer is more reactive than the cis isomer when both substituents are electron-withdrawing. A new method of reactivity comparison of cis- and trans-1,2-DE is proposed in regard to the inductive substituent constant.     

Polymérisation radicalaire du pentadiène-1,3. II. Microstructure des résidus pentadiéniques dans les homo- et copolymères des cis et trans pentadiènes-1,3 avec l'acrylonitrile

The microstructure of diene units was investigated in radical homopolymers of the cis and trans isomers of 1,3-pentadiene and copolymers with acrylonitrile, synthetized in bulk and emulsion. Experiments were carried out by infrared spectroscopy, 100 MHz ¹H-NMR, and 25 MHz ¹³C-NMR studies. No difference between the bulk and emulsion samples was noted. The microstructure of poly(1,3-pentadiene) is practically independent of the cis or trans configuration of the diene monomer and is as follows: 56–59% trans-1,4, 15–17% cis-1,4, 16–20% trans-1,2 7–10% cis-1,2 and 0% 3,4. On the other hand, up to about 30% of incorporated acrylonitrile (10% in the feed), the microstructure of the pentadiene fraction in the copolymers is not affected. This finding suggests that the penultimate unit has very little influence on the polymerization process involving the terminal pentadienly unit. Beyond 10% of acrylonitrile in the feed, the proportions of the structural units were linearly dependent upon the acrylonitrile content: trans-1,4 content increased whereas the amounts of cis-1,4 trans-1,2 and cis-1,2 decreased (except the cis-1,2 fraction, constant in the copolymers from the cis-diene). These results are discussed on the assumption that the microstructure of pentadiene residues is strongly associated with the acrylonitrile comonomer in the feed.     

Topological approach in determining the structure-property dependence in a series of 4-cyclohexene-1,2-dicarboxylic acids

Theoretical information indices of cis- and trans-4-cyclohexene-1,2-dicarboxylic acids and their methyl and dimethyl substituted derivatives are calculated. Correlations between the indices and physicochemical properties of these compounds are analyzed. Original Russian Text Copyright ? 2009 by M. S. Salakhov, B. T. Bagmanov, and O. T. Grechkina __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 1, pp. 183–187, January–February, 2009.     

Massenspektren alicyclischer verbindungen—V : Massenspektrometrische untersuchungen an cyclohexan-(4)-di-carbonsäure-(1,2)-anhydriden

The electron impact mass spectra of 21 4-cyclohexene-1,2-dicarboxylic anhydrides were analysed. It was found that the mass spectrometric fragmentation depends on the constitution, the configuration and the conformation. The intensity of the peak and the abundance of the ratio in cis compounds are greater than in trans isomers. The elemination of CO in the cis compounds is followed by elemination of CO₂H, in the trans isomers by elemination of CO₂.     

Cationic polymerization of 1,3-pentadiene I. infrared, 1H-NMR and 13C-NMR investigations on the microstructure of poly(1,3-pentadiene) synthesized with cationic catalysts

This study deals with cationic polymerization of the cis- and trans-isomers of 1,3-pentadiene. The microstructure of the polymer chains is studied by ¹H-NMR, ¹³C-NMR and IR spectroscopies. It is shown that the trans-diene gives strictly trans-1,4 and trans-1,2 residual linear insaturations, whereas the cis-isomer yields also cis-1,4, cis-1,2 and 3,4-units whose overall content can reach 10 mol-%. According to the cyclization degree of the macromolecules, ranging from 30 to 70 mol-%, the number of trans-(1,2+1,4) units varies between 33 to 65 mol-% and that of trans-1,2 units between 4 and 20 mol-%. An analytical method is proposed to evaluate the average number of rings present in the polycyclic sequences. It is found that the cyclic fragments of the polymer chains consist of bi- or tri-cyclohexane fused rings containing α tetrasubstituted double bond.     

Geometrical isomerism of ethyl N-(2-pyridinyl)aminomethylenecyanoacetates

The pure cis- and trans-isomers of ethyl N-(2-pyridinyl)aminomethylenecyanoacetates were obtained and their structure and their interconvertibility is diseussed. 4H-Pyrido[1,2-a]pyrimidin-4-one-3-carboxylic acids were synthesized by treatment of both cis- and trans-isomers with hydrochloric acid.     

Synthesis,stereochemistry and conformational properties of diastereomeric cyclic dipeptides containing tetrahydro-1,4-thiazine-3,5-dicarboxylic acid

The synthesis of linear dipeptides containing N-protected L-phenylalanine and (3R-cis)-tetrahydro-1,4-thiazine-3,5-dicarboxylic acid dialkyl diester residues is described. N-Deprotection of these dipeptides by hydrogenolysis on palladium afforded directly a mixture of cis and trans dioxopiperazines. The stereochemistry and the solution conformational properties of the cyclic dipeptides are determined.     

Mobility of the ring structure and the characteristics of crosslinked polymers: The structural effect of the eleven-membered ring and its homologs upon the dynamic mechanical properties and glass transition temperature of crosslinked diallyl succinate polymers

Dynamic mechanical properties and glass transition temperatures were measured for crosslinked polymers derived from diallyl succinate monomers. The mobility of the diester having an eleven-membered ring and of homologous structures which are introduced in the crosslinked polymer system, is discussed on the basis of the parameter for cyclization polymerization of a monomer, dynamic mechanical properties, and glass transition temperature. Control of the mobility of the ring structure and its homologous structures involved in the crosslinked polymers was attempted by modification of the substituent at the 1- or 1,2-position of diallyl succinate, and the diallyl succinate monomers were derived from the succinic acid and its derivatives: succinic acid, methyl succinic, ethyl succinic, and chlorosuccinic acids; cis-1,2-dicarboxylic acids of cyclopropane, cyclobutane, cyclopentane, and cyclohexane; cis-1,3- and 1,4-dicarboxylic acids of cyclohexane, and phthalic acid. The results obtained are explained well on the basis of the mobility of the ring and homologous structures.     

Reactions of [Fluoro(methylsulfonyloxy)iodo]benzene: III. Reactions of [Fluoro(methylsulfonyloxy)iodo]benzene with Norbornene and Some Its Derivatives

Reactions of [fluoro(methylsulfonyloxy)iodo]benzene with norbornene, cis-5-norbornene-endo-2,3-dicarboxylic acid, and cis-5-norbornene-endo-2,3-dicarboxylic anhydride were studied. A new mild procedure was developed for introduction of fluoro and sulfonyloxy or two sulfonyloxy groups into molecules of norbornene and its derivatives.     

The crystal structure of a Di(tetramethylammonium)-bis[R,R-tartrato(2-)]-cis-dioxomolybdate(VI), (NMe4)2[MoO2(C4H4O6)2] · EtOH · 1.5 H2O,with comments on tartrate coordination

Summary In the salt (NMe₄[MoO₂(H₂tart)₂] · EtOH · 1.5 H₂O (H₄tart = R,R-(+)-tartaric acid) the tartrato-ligands are linked to molybdenum through a carboxyl oxygen and the vicinal deprotonated hydroxyl oxygen atom, with carboxyl oxygentrans to terminal oxygen of the MoO₂ cis-dioxo core. The configuration about Mo is A. The C-C-C-C torsion angles of the ligands are almost 180°. This enables inter-ligand H-bonding from the uncoordinated hydroxyl groups. The five skeletal atoms from the uncoordinated section of a ligand are nearly co-planar. The probable strong preference fortrans coordination of carboxyl must limit the range of dissolved molybdenum(VI)-tartrate species.     

The cycloaddition of ethylene to butene-2. I. Stereochemistry of the reaction

The rate of the thermal cycloaddition of ethylene to cis and trans butene-2 has been measured at 693°K and at pressures of about 12 atmospheres. The ratio of trans- to cis-1,2-dimethylcyclobutane from the reaction of trans-butene-2 with ethylene was 5.1, obtained from the initial rates of formation of the products. Similarly, the ratio of cis- to trans-1,2-dimethyl-cyclobutane from the reaction of cis-butene-2 with ethylene was 2.8. The results show that the cycloaddition reactions are the reverse of the decomposition reactions of the dimethyl-cyclobutanes and may be interpreted in terms of a biradical intermediate. Several ratios of rate constants have been measured as well as the rate constants for the reaction of the olefins to form the intermediate biradical.     

Single crystal X-ray structure determinations of the reaction products of cis- and trans-cyclohexanedicarboxylic anhydrides and methylhydrazine

The structures of two of the three isomeric products of the reactions between cis- and trans-cyclohexanedicarboxylic anhydrides and methylhydrazine were determined by single-crystal X-ray methods to ascertain their tautomeric forms and stereochemistries. One product was found to be cis-N-methylamino-1,2-cyclohexanedicarboximide and the other trans-hexahydro-2-methylcyclohexa[d]pyridazine-1,2-dione.