Elimination Of Ethane Research Articles

Isomerization of alkane molecular ions

The appearance energies of daughter ions for the major low-energy losses of C/sub 2/H/sub 6/, CH/sub 4/, and CH/sub 3/., of pentane and methylbutane radical cations were measured. The behaviors of a variety of /sup 13/C- and /sup 2/H-labeled compounds were examined. For methylbutane, loss of C/sub 2/H/sub 6/ and CH/sub 3/. yielded ionized propene and 2-butyl cations, at their calculated thermochemical thresholds. Loss of CH/sub 4/ proceeded at an energy greater than that calculated for the production of ionized but-2-ene, methylpropene, but-1-ene, or methylcyclopropane. Ethane elimination is preceded partially (ca. 20 to 25%) by a 1 to 2 methyl shift and a concomitant 2 to 1 H shift; isotope effects associated with this reaction are discussed. For pentane, losses of CH/sub 3/. and CH/sub 4/ take place at the same energy, corresponding to the calculated threshold for production of the secondary cations; /sup 13/C labelling experiments showed that the penultimate C atoms are not lost but that C-3 is lost (46%) in these reactions, with an ease similar to terminal C atom losses (54%). /sup 2/H labelling permitted the separation of the metastable peak for methane loss into components having different kinetic energy releases attributable to the production ofmore » different (C/sub 4/H/sub 8/)/sup +/. daughter ions. Although C/sub 2/H/sub 6/ loss was observed to take place at energies down to the calculated thermochemical threshold for generation of ionized propene, the appearance energy of the metastable peak was the same as that for CH/sub 3/. and CH/sub 4/ losses. Labelling experiments showed that the central C atom is not lost in this reaction. Detailed analysis of the observations leads to the conclusion that the CH/sub 3/., CH/sub 4/, and C/sub 2/H/sub 6/ eliminations from pentane radical cations are preceded by an isomerization to energy-rich ionized methylbutane. 2 figures, 3 tables.« less

ChemInform Abstract: THE 147‐NM PHOTOLYSES OF TETRAMETHYLENE SULFIDE, TETRAMETHYLENE SULFOXIDE, AND TETRAMETHYLENE SULFONE

Tetramethylene sulfide, sulfoxide, and sulfone have been photolyzed with 147-nm radiation in the gas and condensed phases. Mechanisms which assume diradical intermediates are presented for the photodecomposition of each compound. The major reaction in all three cases is the elimination of ethylene by a ..beta..-cleavage of the initially formed diradical: XCH/sub 2/CH/sub 2/CH/sub 2/CH/sub 2/. ..-->.. .XCH/sub 2/CH/sub 2/. + C/sub 2/H/sub 4/. The competing ..beta..-cleavage produces X==CH/sub 2/ and C/sub 3/H/sub 6/. This second ..beta..-cleavage is less important in the sulfoxide and the sulfone than it is in the sulfide. The direct elimination of the sulfur atom, and any attached oxygen atoms, is of no importance in the sulfide and of increasing importance as the oxidation state of the sulfur atom increases. The similarity between the mass spectral fragmentation and the vacuum ultraviolet photochemistry of these compounds is noted and the possible involvement of triplet states is mentioned.

Gas-phase thermolyses. Part 8. Gas-phase thermolysis of methyl and ethyl monothioacetates

The unimolecular gas-phase thermolyses of the four methyl and ethyl monothioacetates (5)–(8) have been studied by the flash vacuum thermolysis–field ionization mass spectrometry technique in the temperature range 883–1 404 K. The types of reactions verified were keten formation, thiono–thiolo rearrangement, and, in the case of the ethyl esters, ethylene elimination. The possible mechanisms for keten formation are discussed, and it is concluded that the thiono-carboxylates eliminates the mercaptan via an enethiolized structure, whereas the decomposition of the thiolo-esters apparently proceeds via direct 1,2-elimination of the thiols.

The 147-nm photolyses of tetramethylene sulfide, tetramethylene sulfoxide, and tetramethylene sulfone

Tetramethylene sulfide, sulfoxide, and sulfone have been photolyzed with 147-nm radiation in the gas and condensed phases. Mechanisms which assume diradical intermediates are presented for the photodecomposition of each compound. The major reaction in all three cases is the elimination of ethylene by a ..beta..-cleavage of the initially formed diradical: XCH/sub 2/CH/sub 2/CH/sub 2/CH/sub 2/. ..-->.. .XCH/sub 2/CH/sub 2/. + C/sub 2/H/sub 4/. The competing ..beta..-cleavage produces X==CH/sub 2/ and C/sub 3/H/sub 6/. This second ..beta..-cleavage is less important in the sulfoxide and the sulfone than it is in the sulfide. The direct elimination of the sulfur atom, and any attached oxygen atoms, is of no importance in the sulfide and of increasing importance as the oxidation state of the sulfur atom increases. The similarity between the mass spectral fragmentation and the vacuum ultraviolet photochemistry of these compounds is noted and the possible involvement of triplet states is mentioned.

ChemInform Abstract: INFRARED PHOTOCHEMISTRY OF CYCLOBUTYL CHLORIDE

The decomposition of cyclobutyl chloride following multiple infraredphoton excitation has been investigated. The primary photolysis products are butadiene, from elimination of HCl, and ethylene and vinyl chloride, fromring scission. The vinyl chloride undergoes secondary decomposition to acetylene and HCl. In addition to these products, known from thermal VLPP experiments, we also find 1-butene, which may arise from a higher energy CCl homolysis channel. Collisions with either reactant molecules oradded buffer gas lead to cooling of the laser-produced vibrational energy distributions. The average amount of energy removed per collision is 15–20 kcal/mol for self-collisions and 2–4 kcal/mol with argon.

Thermal isomerization and decomposition of 3,3-diethyl-2,4-dimethyl-3-silathietane

Pyrolysis of 3,3-diethyl-2,4-dimethyl-3-silathietane (I) has been studied at temperatures from 300 to 530°C using the pulse pyolytic GC-MS method. Decomposition of I proceeds with the elimination of ethane, ethylene, propylene, butadiene, cis- and trans-but-2-ene, and also with the loss of atomic sulphur. Isomerization into sulphur-containing unsaturated compounds is the main transformation process of I. The intermediacy of 1,1-diethyl-2-methyl-1-silaethylene and diethylsilathione is also discussed.

Mechanisms of 1,1-reductive elimination from palladium: elimination of ethane from dimethylpalladium(II) and trimethylpalladium(IV)

Mechanisms of 1,1-reductive elimination from palladium: elimination of ethane from dimethylpalladium(II) and trimethylpalladium(IV)

Infrared photochemistry of cyclobutyl chloride

AbstractThe decomposition of cyclobutyl chloride following multiple infraredphoton excitation has been investigated. The primary photolysis products are butadiene, from elimination of HCl, and ethylene and vinyl chloride, fromring scission. The vinyl chloride undergoes secondary decomposition to acetylene and HCl. In addition to these products, known from thermal VLPP experiments, we also find 1‐butene, which may arise from a higher energy CCl homolysis channel. Collisions with either reactant molecules oradded buffer gas lead to cooling of the laser‐produced vibrational energy distributions. The average amount of energy removed per collision is 15–20 kcal/mol for self‐collisions and 2–4 kcal/mol with argon.

Beitrag zur massenspektrometrischen retro‐Diels‐Alder‐Reaktion: 1,2,3,4‐Tetrahydrophenanthren. 35. Mitteilung über massenspektrometrische Untersuchungen

Contribution to the Mass Spectral retro‐Diels‐Alder Reaction: 1,2,3,4‐Tetrahydrophenanthrene[1,4‐13C]‐1,2,3,4‐Tetrahydrophenanthrene (1) was synthesized starting from [1,4‐13C]‐succinic acid. The mass spectral behavior (EI./MS., 70eV) of 1 is very similar to that of tetraline [2] concerning its loss of ethylene from the molecular ion. Similarly the fragmentation reaction of the synthetic precursors, ketones 7 and 8, seems to partly undergo a carbon rearrangement reaction prior to the elimination of ethylene which is unlike to the behavior of α‐tetralone.

Monitoring lipid peroxidation by breath analysis: Endogenous hydrocarbons and their metabolic elimination

Monitoring of ethane and pentane in breath as a noninvasive method to measure lipid peroxidation is performed by an increasing number of laboratories. The alkanes are generated through peroxidative breakdown of polyunsaturated fatty acids. Fasted Sprague-Dawley rats exhale these hydrocarbons at a rate of approximately 1.7 nmol/kg·hr. Through an improved analytical procedure other volatile hydrocarbons could be detected in the breath of the animals, i.e., ethene (1.1 nmol/kg·hr), propane (0.7 nmol/kg·hr), n-butane (0.7 nmol/kg·hr), iso-pentane, and iso-butene. The exhaled hydrocarbons accumulate in the atmosphere if an animal is confined in a closed system. However, the increase is not linear but a steady-state concentration is approached, presumably due to reuptake and subsequent hepatic metabolism. Hydrocarbons are oxidized by the hepatic monooxygenases, at rates increasing with their molecular masses. The same has been found for the elimination of ethane, propane, butane, pentane, and iso-butene by a rat from closed system. Metabolism is inhibited by a variety of substances, e.g., dithiocarb, ethanol, and tetrahydrofurane. Therefore, the increased release of hydrocarbons into the gas phase, after treatment with compounds suspected to induce lipid peroxidation, may merely result from decreased metabolism. Especially if the hydrocarbon exhalation is only moderately elevated as after ethanol administration, this aspect must be taken into account. Similarly, peroxidizing microsomes show elevated hydrocarbon output when treated with carbon monoxide in order to block metabolism. This study provides a procedure for discrimination of inhibitory and peroxidative action which is of particular importance if the increase over control levels is only moderate. In addition, it may serve as monitor for the metabolic capacity of a laboratory animal.

Mechanisms of 1,1-reductive elimination from palladium

The 1,1-reductive elimination of ethane from three cis-bis(phosphine)dimethylpalladium complexes, L/sub 2/Pd(CH/sub 3/)/sub 2/ (L = PPh/sub 3/,PPh/sub 2/CH/sub 3/; L/sub 2/ = Ph/sub 2/PCH/sub 2/CH/sub 2/PPh/sub 2/), and three trans analogues (L = PPh/sub 3/, PPh/sub 2/CH/sub 3/; L/sub 2/ = 2,11-bis(diphenylphosphinomethyl)benzo(c)phenanthrene (TRANSPHOS) was carried out. The three cis complexes underwent reductive elimination in the presence of coordinating solvents (Me/sub 2/SO, DMF, THF). The trans complexes which could isomerize to cis (L = PPh/sub 3/,PPh/sub 2/CH/sub 3/) did so in polar solvents and then underwent reductive elimination. (TRANSPHOS)dimethylpalladium would not undergo eductive elimination of ethane, even at 100/sup 0/C in Me/sub 2/SO. The eliminations from the cis isomers were intramolecular as determined by the lack of crossover with the perdeuteriomethylpalladium analogue and displayed first-order kinetics (k = 1.04 x 10/sup -3/s/sup -1/, L = PPh/sub 3/, 60/sup 0/C; K = (6.5 to 9.5) X 10/sup -5/s/sup -1/, L = PPh/sub 2/CH/sub 3/, 60/sup 0/C; k = 4.78 x 10/sup -7/s/sup -1/, L/sub 2/ = Ph/sub 2/PCH/sub 2/CH/sub 2/PPh/sub 2/, 80/sup 0/C). The presence of diphenylacetylene in the reaction mixture traps the palladium(0) product as the bis(diphenylmethylphosphine)(diphenylacetylene)palladium complex. Although (TRANSPHOS)dimethylpalladium would not undergo a 1,1-reductive elimination of ethane, the addition ofmore » CD/sub 3/I to a Me/sub 2/SO solution of this complex at 25/sup 0/C rapidly produced CD/sub 3/-CH/sub 3/, implicating a transient palladium(IV) intermediate. 5 figures, 4 tables.« less

An Experimental and Theoretical Study of the Degenerate Carbon Skeleton Isomerization of the Cyclopentyl Cation in the Gas Phase

The non-classical pyramidal cation (4) provides a rational explanation of all the phenomena observed on mass-spectrometic degradation of the cyclopentyl cation (1). On generation from (2a), (2b), (3a), or (3b) (• = 13C), (1) always gives 13C2H4, 13C12CH4, 12C2H4 in the ratio of 10:60:30, i.e. all the C atoms must have become statistically equivalent prior to elimination of ethylene from (1). MINDO/3 calculations show degradation to proceed via the cations (4) and (5).

Darstellung und stabilität von n, n-disubstituierten β-aminoethyl-magnesiumbromiden; die ersten β-heteroatomsubstituierten grignardverbindungen des typs R 2NCH 2CH 2MgX

R 2NCH 2,CH 2BR (R 2 = Ph 2; Ph, Me; (C 6H 11) 2)reacts with highly activated magnesium between −75 and −100°c in THF and ether to give the Grignard compounds R 2NCH 2CH 2MgBr, which already decompose between −90 and−20°c by elimination of ethylene. The thermal stability increases in the sequence R 2 = Ph, Me < Ph 2 < (C 6H 11).

Rare-gas sensitized radiolysis of gaseous isobutene: ionic processes

Irradiation of isobutene at low pressure in the presence of suitable scavengers or mixed with the rare gases Ar, Kr, and Xe shows that 2-methyl-but-2-ene is partially formed in ionic processes. These processes involve polymeric ions of isobutene formed in "head-to-head" reactive encounters with neutral isobutene. The resulting ionic species, which have internal structural tension, can isomerize with a subsequent elimination of ethylene, or decompose to give 2-methyl-but-2-ene. The rare-gas sensitized radiolysis confirms the already established reaction channels for formation of the main products.

Photoionization study of ion-molecule reactions in isobutylene

Ion—molecule reactions of gaseous isobutylene were investigated in a high-pressure photoionization mass spectrometer up to a pressure of 3 torr. With increasing pressure the reaction sequence is complicated by the occurrence of many condensed ionic species, which can be grouped into four families: [C 4H 9(C 4H 8) n ] +, [C 9H 15(C 4H 8) m ] +, [C 7H 15(C 4H 8) p ] + and [C 10H 21(C 4H 8) q ] +. The last two families of ionic species seem to originate from the [C 4H 9 (C 4H 8) n ] + ions by elimination of neutral ethylene or isomeric pentene fragments during condensation steps. On the other hand, the C 9H 15 + ion, which starts the [C 9H 15(C 4H 8) m ] + polymerization sequence, seems to result from the interaction of the C 8H 14 + with neutral isobutylene molecules.

Electrophilic aromatic reactivities via pyrolysis of 1-arylethyl esters. Part 19. Substitutent effects in pyridine

Rates of pyrolysis of some 4-, 5-, and 6-substituted 1-(2-pyridyl)ethyl acetates have been measured between 637.5 and 695.4 K. The data show that the electrophilic substituent constants which apply to substituted benzenes, do not describe the effects of these substituents in pyridine. For example, the 5-methyl and 5-chloro substituents, respectively, activate and deactivate the 2-position less than they affect a para-position in benzene, yet the 4- and 6-methyl substituents activate more than they affect a meta-position in benzene. Moreover the methyl substituent activates the 2-position more from the 6- than from the 4-position, as it does in the related SN1 solvolysis of 2-aryl-2-chloropropanes. The differential effect is however proportionally much smaller in the gas phase indicating that steric hindrance of hydrogen bonding may be mainly responsible for the abnormally high reactivity of 6-substituted 2-chloro-2-(2-pyridyl)propanes in the solvolysis. Elimination of acetic acid from 1-(6-ethoxy-2-pyridyl)-ethyl acetate is accompanied by elimination of ethylene from the ethoxy group to give 6-vinyl-2-pyridone. This new gas-phase elimination is a nitrogen analogue of acetate pyrolysis.

Reactions of ethylaluminium compounds with p-chloranil

Reactions of ethylaluminium dichloride, diethylaluminium chloride and triethylaluminium with p-chloranil have been investigated. Tetrachlorohydroquinone and p-ethoxytetrachlorophenol are the main reaction products after hydrolysis. Ethane, ethylene, butane, hexane, octane, higher aliphatic hydrocarbons, products of the chlorine substitution by an ethyl group in a molecule of p-chloranil or tetrachlorohydroquinone, and ethyltoluene or benzyltoluene isomers (when toluene was used as a solvent) may also be formed depending on the type of reactants and reaction conditions. The reactions with p-chloranil of the ethylaluminium compounds studied were found to proceed involving in the first step the formation of donor—acceptor complexes via the carbonyl group. These complexes were found to undergo reactions of two basic types. The first one is a homolytic dissociation of the AlC bond with the formation of an aluminium derivative of semiquinone and an ethyl radical. The second type of reaction is the hydrogen transfer from the ethyl group bonded with the aluminium atom to the carbonyl group of quinone with the elimination of ethylene. The reaction course leading to the formation of tetrachlorohydroquinone and p-ethoxytetrachlorophenol is proposed and discussed.

Mass spectra of ferrocenophanes. Cyclic peroxide derivatives

AbstractThe electron impact mass spectra of two 6‐membered cyclic peroxides of ferrocenophane depend sensitively on the temperature of the sample heater of the direct inlet system. It is confirmed that their spectra contain some fragment ion peaks arising from thermal decomposition or rearrangement products, but that the ion at m/e (M–28) is due to elimination of ethylene from the molecular ions of the peroxides by a retro Diels‐Alder type reaction.

Thermal conversion of 2-ethoxypyridine into 2-pyridone; an analogue of ester pyrolysis

2-Ethoxypyridine undergoes thermal elimination of ethylene to give 2-pyridone via a 6-centred cyclic process which is a nitrogen analogue of ester pyrolysis.

13C magnetic resonance studies 70. The behavior of bicyclo[2.2.2]octenone under strongly basic conditions. A competition between retro Diels–Alder and Haller-Bauer-cleavages

As a test for possible competitive α- and β-enolization in bicyclic ketones the behavior of bicyclo[2.2.2]octenone in t-BuO−–t-BuOH at 185 °C has been examined. The major reaction (∼90%) involves Claisen condensation followed by retro Diels-Alder elimination of ethylene and Haller–Bauer cleavage. All acidic and phenolic components, accounting for 90% of the product, have been identified and characterized, primarily by their 13Cmr spectra.