An investigation of the mechanism of single and double hydrogen atom transfer reactions in alkyl benzoates by the <i>ortho</i> effect

Tajima, Susumu; Azami, Tadashige; Shizuka, Haruo; Tsuchiya, Toshikazu

doi:10.1002/oms.1210140908

Cited by 18 publications

(4 citation statements)

References 15 publications

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“…The formation enthalpy of NAIPE is calculated from two pathways, summarized by reactions (19) and (22). At first, the bond energy portability is used for the dissociation reaction (19) according to Benson's additivity method. 41…”

Section: Nicotinic Acid Isopropyl Estermentioning

confidence: 99%

“…Reactions (19) to (21) are simple bond cleavages, which are regarded to occur without additional activation energy.…”

Section: Nicotinic Acid Isopropyl Estermentioning

confidence: 99%

“…However, the detailed mechanism is still under debate between a concerted and a stepwise mechanism via formation of an intermediate distonic ion [6][7][8] by g-hydrogen shift and subsequent homolytic C-C bond cleavage to yield uncoordinated free products. The stepwise mechanism is strongly favored, [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] mainly based on arguments concerning the lifetime of intermediates 12 and the competitive H/D exchange in some isotopically labelled ketones prior to the C-C bond cleavage, depending on the stability of the intermediate distonic ion with branched and straight aliphatic chains 13 or the product stability. 14 An extension of the last step assumes the formation of an ion/molecule complex as intermediate for the products but also for intra-cage reactions like hydrogen scrambling or a further hydrogen transfer.…”

Section: Introductionmentioning

confidence: 99%

“…The McL2H rearrangement with a double hydrogen transfer results in the formation of protonated organic acids and corresponding allylic alk-1-en-3-yl radicals. Mechanistic aspects for this rearrangement cover a sequential twostep reaction, 18 a concerted reaction in isopropyl esters 19 or an intermediate ion/molecule complex 20 for esters with a long aliphatic chain.…”

Section: Introductionmentioning

confidence: 99%

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Electron-induced ionization of undeuterated and deuterated benzoic acid isopropyl esters and nicotinic acid isopropyl esters: Some implications for the mechanism of the McLafferty rearrangement

Opitz

Hashmi

Miehlich

et al. 2019

Eur J Mass Spectrom (Chichester)

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Electron ionization mass spectra, ionization, and appearance energies and bond energies (as dissociation energies) are reported for benzoic acid-1-methyl-ethyl ester (BAIPE), benzoic acid-1-deutero-1-methyl-ethyl ester (BAIPED1), benzoic acid-2,2,2-trideutero-1-trideuteromethyl-ethyl ester (BAIPED6) as well as nicotinic acid-1-methyl-ethyl ester (NAIPE), nicotinic acid-1-deutero-1-methyl-ethyl ester (NAIPED1), and nicotinic acid-2,2,2-trideutero-1-trideuteromethyl-ethyl ester (NAIPED6). Ionization energies of 9.39 eV for BAIPE, 9.40 eV for BAIPED1, 9.26 eV for BAIPED6 as well as 9.70 eV for NAIPE, 9.79 eV for NAIPED1, and 9.65 eV for NAIPED6 were determined. A gas-phase formation enthalpy of [Formula: see text] = (−4.10 ± 0.1) eV for BAIPE is calculated as well as [Formula: see text] = (−3.35 ± 0.1) eV for NAIPE. Molecular ions show two main fragmentation pathways. The first is a classical McLafferty rearrangement, characterized by the transfer of one γ-hydrogen atom from the isopropyl ester chain leading to the ions of the corresponding acid and neutral propene. The second is the double hydrogen transfer from the ester chain leading to the formation of the protonated acid and a C3H5√ allyl radical. For BAIPE, both hydrogen atoms originate from the methyl groups of the aliphatic chain with a probability of ≥98%, whereas the C-1-hydrogen is transferred with a probability of ≤2%. For NAIPE, both hydrogen atoms originate from the methyl groups of the aliphatic chain with a probability of 90%. Experimental proton affinities of PA = (8.75 ± 0.2) eV for benzoic acid and PA = (8.43 ± 0.2) eV for nicotinic acid are derived. For the protonation of the carbonyl group, B3LYP DFT calculations yielded PA = 8.66 eV for benzoic acid and PA = 8.41 eV for nicotinic acid. The overall fragmentation mechanism is explained with the initial formation of a 1,5-distonic ion by transfer of the first hydrogen. For the transfer of the second hydrogen, an intermediate ion/neutral complex is formulated.

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Section: Nicotinic Acid Isopropyl Estermentioning

confidence: 99%

“…Reactions (19) to (21) are simple bond cleavages, which are regarded to occur without additional activation energy.…”

Section: Nicotinic Acid Isopropyl Estermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Electron-induced ionization of undeuterated and deuterated benzoic acid isopropyl esters and nicotinic acid isopropyl esters: Some implications for the mechanism of the McLafferty rearrangement

Opitz

Hashmi

Miehlich

et al. 2019

Eur J Mass Spectrom (Chichester)

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Temperature effect on the single and double hydrogen atom transfer reactions in o‐, m‐and p‐toluic acid butyl esters

Tajima

Yanagisawa

Azami

et al. 1980

Org. Mass Spectrom.

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INTRODUCXIONBoth single and double hydrogen atom transfer reactions (1) and (2) paper, it has been reported4 from the m a s spectra of alkyl o-hydroxybenzoates (alkyl salicylates) and alkyl p-hydroxybenzoates that the intramolecular hydrogen bond' (interaction between the hydrogen atom in the hydroxyl group and the oxygen atom in the carboxyl group) may prevent the second hydrogen atom transfer.In the present paper, the temperature effect on the abundances of the rnlz 137 and mlz 136 ions generated by the reactions (2) and (1) RESULTS AND DISCUSSIONIn the mass spectra of alkyl p-hydroxybenzoates, both rnlz 139 and rnlz 138 ions from reactions (2) and (1) were found? In contrast, only the single hydrogen atom transferred ion at mlz 138 was found in the spectra of alkyl salicylates, which have a hydroxyl group with a strong electron-donating property at the ortho p~s i t i o n .~In the case of toluic acid butyl esters, which have a methyl group with a weaker electron-donating property, the abundances of rearrangement ions caused by reactions (1) and (2) which occur at rnlz 136 and m/z 137 became quite intense. The mass spectra of the compounds studied are shown in Table 1

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The mass spectrum of isopropyl o‐toluate

Tajima

Yanagisawa

Azami

et al. 1981

Org. Mass Spectrom.

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The formation of an [M + 1]+ ion and the fragmentation of isopropyl o‐toluate have been investigated by the deuterium labelling technique and kinetic energy release measurements. The hydrogen atom involved in the [M + 1]+ ion formation does not originate from a specific part of the molecule, but from all parts. A small amount of hydrogen exchange between the secondary carbon atom in the isopropyl group and the carbon atoms in the tolyl group takes place prior to decomposition of the molecular ion into the m/z 136 ion by a McLafferty rearrangement. Either almost complete scrambling of the hydroxyl hydrogen atom and the methyl hydrogen atoms in tolyl group or an almost equilibrated exchange of the hydroxyl hydrogen atom with one of the remaining hydrogen atoms in tolyl group also takes place prior to the elimination of a water molecule from the intermediate m/z 136 ion.

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An investigation of the mechanism of single and double hydrogen atom transfer reactions in alkyl benzoates by the ortho effect

Abstract: Single and double hydrogen atom transfers in reactions (1) and (2) in the mass spectra of ethyl benzoate, isopropyl benzoate, and isobutyl benzoate have been investigated 6 t h reference to the orfbo effect: (1)

Cited by 18 publications

References 15 publications

Electron-induced ionization of undeuterated and deuterated benzoic acid isopropyl esters and nicotinic acid isopropyl esters: Some implications for the mechanism of the McLafferty rearrangement

Electron-induced ionization of undeuterated and deuterated benzoic acid isopropyl esters and nicotinic acid isopropyl esters: Some implications for the mechanism of the McLafferty rearrangement

Temperature effect on the single and double hydrogen atom transfer reactions in o‐, m‐and p‐toluic acid butyl esters

The mass spectrum of isopropyl o‐toluate

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