Intramolecular Hydrogen Abstraction Research Articles

Tridentate chelate π-bonded complexes of rhodium(I), iridium(I), and iridium(III) and chelate σ-bonded complexes of nickel(II), palladium(II), and platinum(II) formed by intramolecular hydrogen abstraction reactions

2,2′-Bis( o-diphenylphosphino)bibenzyl, o-Ph 2PC 6H 4CH 2CH 2C 6H 4PPh 2- o (bdpbz), is dehydrogenated by various rhodium complexes to give the planar rhodium(I) complex ▪, from which the ligand, 2,2′-bis( o-diphenylphosphino)- trans-stilbene (bdpps) can be displaced by treatment with sodium cyanide. The stilbene forms stable chelate olefin complexes with planar rhodium(I) and iridium(I) and with octahedral iridium(III). On reaction with halide complexes of nickel(II), palladium(II) or platinum(II), the stilbene ligands ▪ (R  Ph or o-CH 3C 6H 4) lose a vinyl proton in the form of hydrogen chloride to give chelate, planar σ-vinyls of general formula MX(o-R 2PC 6H 4C CHC 6H 4PR 2- o) (M  Ni, Pd, Pt; X  Cl, Br, I) of high thermal stability; analogous methyl derivatives Pt(CH 3)(o-R 2PC 6H 4C CHC 6H 4PR 2- o) are obtained from Pt(CH 3) 2(COD) (COD  1,5-cyclooctadiene) and the stilbene ligands. The bibenzyl also forms chelate σ-benzyls MX(o-Ph 2PC 6H 4C HCH 2C 6H 4PPh 2- o) (M  Pd, Pt; X  Cl, Br, I). The 1H NMR spectra of the o-tolyl methyl groups in the compounds MX(o-R 2PC 6H 4C CHC 6H 4PR 2- o) (M  Ni, Pd, Pt; R  o-CH 3C 6H 4) vary with temperature, probably as a consequence of interconversion of enantiomers arising from restricted rotation about the MP and MC bonds. Possible mechanisms for the dehydrogenation reactions are briefly discussed.

Photochemistry in the Adsorbed Layer. V. Effects of Surface Pretreatments upon the Photolysis of Adsorbed 2-Pentanone

Abstract The effects of surface pretreatment upon the photolysis as well as the absorption and phosphorescence spectra of 2-pentanone adsorbed on porous Vycor glass have been investigated. The rate of propane formation (Norrish type I reaction) passes through a maximum and then decreases at higher degassing temperatures, while that of ethylene formation (Norrish type II reaction) decreases with increasing degassing temperature. Simultaneously, the phosphorescence intensity increases while the blue shift of the (n,π*) band decreases. This suggests that with a rise in degassing temperature the triplet lifetime increases while the surface polarity decreases. Thus, the decrease in the rate of ethylene formation is attributed to destabilization of the 1,4-biradicals formed by the intramolecular hydrogen abstraction, and the decrease in the rate of propane formation to the decrease in the lifetime of the n-propyl radicals, the hydrogen abstraction efficiency, and the probability of α-cleavage.

Photochemical Deuteration of ortho-Substituted N-(Diphenylmethylene)acetamides

Abstract The alkyl hydrogens of N-(2-alkyldiphenylmethylene)acetamides were found to be readily replaced with deuterium on irradiation in deuteriomethanol (CH3OD). It is proposed that the deuteration proceeds via an enamide isomer produced by intramolecular hydrogen transfer from the o-alkyl group to the excited C=N double bond. An intermolecular hydrogen atom abstraction pathway was excluded because neither N-(4-methyldiphenylmethylene)acetamide in deuteriomethanol(CH3OD) nor diphenylmethane in deuteriomethanol(CH3OD) in the presence of N-(diphenylmethylene)acetamide was deuterated. Intramolecular hydrogen abstraction is essential for the deuteration, because no deuteration occurs on irradiation of 2-methylbenzophenone semicarbazone which undergoes no photoreduction. The difference in reactivities of the ortho-substituted imines between in solution and in a rigid matrix is discussed from the viewpoint of syn-anti isomerization.

On the relationship between intramolecular hydrogen abstraction by alkoxyl radicals and deshielding by the corresponding hydroxy-groups as indicated by nuclear magnetic resonance

The 1H n.m.r. spectra of various steroids and triterpenoids and their hydroxy-derivatives have been studied. It is shown that a consideration of deshielding by hydroxy-groups can provide valuable information on the likely course of intramolecular hydrogen abstraction reactions of alkoxyl radicals.

Intramolecular hydrogen abstraction of the vibrationally excited triplet state of simple alkenes

The vibrationally excited triplet generated in the mercury photosensitisation of hex-1-ene and cis-oct-2-ene underwent intramolecular hydrogen abstraction via a six-membered transition state and subsequent β-cleavage and recombination of the resulting 1,4-biradical.

Electronic ground state structure and chemistry of nitroguanidine

VESCF(BJ)CI MO reactivity indices were used to provide a consistent rationale for the ground state structure, thermal decomposition and chemistry of nitroguanidine (1). Intra- and inter-molecular NH...O and NH...N hydrogen bonds, attractive and repulsive coulombic forces between nitrogen and oxygen atoms, appear to determine the crystal structure of (1). An intramolecular hydrogen-abstraction reaction and the cleavage of the molecule's weakest bond, viz. (H2N)2C-NNO2, appear to be the main primary thermal decomposition pathways for (1). The nitrimino nitrogen atom and the carbon atom were postulated to be the centres of electrophilic and nucleophilic substitution reactions respectively.

Computer simulation of intramolecular hydrogen abstraction in the photochemistry of p-benzophenonecarboxylate esters

Computer simulation of intramolecular hydrogen abstraction in the photochemistry of p-benzophenonecarboxylate esters

The Photochemical Reaction of α-Diketones

Abstract The relative photochemical reactivity of α-diketones, in particular, 9,10-phenanthraquinone, 1,2-naphthoquinone, acenaphthoquinone, benzil, 4,4′-dimethylbenzil, 2,4,6-trimethylbenzil, 2,5,2′,5′-tetramethylbenzil, 2,3,5,6-tetramethylbenzil, 2,4,6,2′,4′,6′-hexamethylbenzil, phenylglyoxal, 2,5-dimethylphenylglyoxal, and 2,4,6-trimethylphenylglyoxal was investigated in hydrogen donating solvents. Type of the product and relative reactivity differ widely according to the structure of α-dike tones. Whereas 9,10-phenanthraquinone gives 1,4-adduct (V) in a hydrogen donating solvent (THF), 2,5,2′,5′-tetramethylbenzil gives 2-hydroxy-2-(2′,5′-dimethylphenyl)indanone (VII) via intramolecular hydrogen abstraction in nearly quantitative yield. No photochemical reaction of 2,4,6-trimethylbenzil or 2,3,5,6-tetramethylbenzil could be observed in the same solvent even under a long irradiation.

Effective Intramolecular Hydrogen Abstraction by the Sulfonamide Radical

Abstract To study the reactivity of the sulfonamide radical in various reaction systems, the photodecomposition of N-t-butyl and N-methyl-N-chloroalkanesulfonamides was investigated. In benzene, the competitive hydrogen abstraction by the chlorine atom occurred to an appreciable extent and the participation of the chlorine atom was retarded with N2-flow control. In an aqueous solution (AcOH-H2O, t-BuOH-H2O), the quantitative conversion to γ-and δ-chloroalkanesulfonamide was observed; this was thought to be due to the intramolecular hydrogen abstraction by the sulfonamide radical and to the lowering of the reactivity of the chlorine atom because of the solvation by H2O. In an acid solution (AcOH-H2O-H2SO4), a higher preference for 1,5 hydrogen transfer was found; this was caused by the protonated sulfonamide radical. The formation ratio of γ- to δ-chloroalkanesulfonamide in several solvents was determined, and the reactivity of the sulfonamide radical was discussed. From the reaction products obtained, several aliphatic sultams were synthesized.

Photochemistry of o-benzyloxyphenylglyoxylates. A case of favored intramolecular hydrogen abstraction via a seven-membered cyclic transition state

Photochemistry of o-benzyloxyphenylglyoxylates. A case of favored intramolecular hydrogen abstraction via a seven-membered cyclic transition state

Photoinduced reactions—XXVIII : Competition between intramolecular hydrogen abstraction and fragmentation in the photoreaction of hindered aromatic ketones and a correlation with the mass spectra

The photoreactions of various alkyl 2,4,6-trimethylphenyl ketones bearing a sterically hindered CO group have been investigated. Depending upon the bulkiness of the alkyl side chain, two types of reactions have been observed. Intramolecular hydrogen abstraction leading to formation of a novel benzocyclobutenol is predominant with a less bulky alkyl side chain and fragmentation leading to a carbonyl—alkyl bond fission with a more bulky one. A correlation is found between the photoreactions and the mass spectrometric decomposition of the ketones. These photoreactions have been interpreted in terms of stereoelectronic requirements for the hydrogen abstraction from the n,π * triplet state. Unusual photoreduction of 2,4,6-trimethylbenzophenone is also reported.

Quantitative aspects of alkylperoxy radical isomerization during hydrocarbon combustion

Detailed studies of the distribution of the products formed in the different regimes of combustion of n -pentane indicate the importance in the overall oxidation mechanism of the isomerization of amylperoxy radicals. It has been shown that C 5 O -heterocycles and C 5 alkenes are formed as a result of the intramolecular rearrangement of such radicals but that O -heterocycles, carbonyl compounds and alkenes of carbon-number less than five are produced in other ways. The experimental results suggest that, under cool-flame conditions where the yields of C 5 O -heterocycles and C 5 alkenes are highest, between 40 and 50% of the initially formed amylperoxy radicals undergo isomerization followed either by O—O bond fission and cyclization or by C—O bond fission. Then nature and amounts of the various O -heterocyclic products formed from n -pentane enable deductions to be made firstly as to the extents of initial oxidative attack of the hydrocarbon at different skeletal positions and secondly as to the relative susceptibilities of the different C—H groups to intramolecular hydrogen abstraction by the outer oxygen atom of the amylperoxy radical.

Alkylperoxy radical isomerization and cool flames

Studies of the combustion of n -hexane with special reference to the O -heterocyclic products formed show that these compounds are present in the largest quantities under cool flame conditions and that their concentration decreases sharply at the ignition boundary. O -heterocyclic compounds appear to be the main products of the intramolecular rearrangement of hexylperoxy radicals and their structure shows that they are derived predominantly from the 2-hexylperoxy radical. The amounts of the different O -heterocycles produced can, on the basis of reasonable assumptions, provide information regarding the relative susceptibility to intramolecular hydrogen abstraction of the 3-, 4- and 5-positions in the 2-hexylperoxy radical.

Intramolecular Hydrogen Abstraction in a Primary Alkoxy Radical

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIntramolecular Hydrogen Abstraction in a Primary Alkoxy RadicalE. L. JennerCite this: J. Org. Chem. 1962, 27, 3, 1031–1032Publication Date (Print):March 1, 1962Publication History Published online1 May 2002Published inissue 1 March 1962https://doi.org/10.1021/jo01050a502RIGHTS & PERMISSIONSArticle Views294Altmetric-Citations15LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (254 KB) Get e-Alerts Get e-Alerts