Dissociation of chloride from ortho-, meta- and para-chloromethylphenoxides: The enthalpy of formation of meta-quinomethane

Chacko, Silvi A.; Wenthold, Paul G.

doi:10.1016/j.ijms.2007.02.052

Cited by 12 publications

(8 citation statements)

References 56 publications

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“…The meta-benzoquinomethane diradical is known to be much less stable than the closedshell ortho-and para-isomers. 56 Our calculations suggest that its triplet state lies ca. 108 kJ mol -1 above the para-isomer and that the singlet-triplet energy difference is ca.…”

Section: + H] + [3 + H] + and [4 + H] + Namely Benzylic C-c Bond mentioning

confidence: 77%

Fragmentation of Protonated 2-(2-Phenylethyl)Chromones from Agarwood: The Diagnostic Role of Ion/Neutral Complexes as Reactive Intermediates

Yang

Xia

Jiang

et al. 2015

Eur J Mass Spectrom (Chichester)

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A positive-ion electrospray ionisation collision-induced dissociation mass spectrometric study on the fragmentation of the [M + H](+) ions of 2-(2-phenylethyl)chromone and a set of nine hydroxyl- and/or methoxy-substituted derivatives has revealed a highly prominent fragmentation channel, the loss of benzoquinomethanes or a benzaldehyde, respectively, as a diagnostic feature for 2-(2-phenylethyl)chromones that bear a hydroxyl group at the para- (4'-), ortho- (2'-) and/or benzylic (α-) position of the phenylethyl residue. Derivatives that bear only a meta- (3'-) hydroxyl group do not undergo this elimination. The intermediacy of ion/neutral complexes (INCs) is invoked to explain this fragmentation, which involves the remarkable intra-complex proton or hydrogen atom transfer from the remote 4'-OH (or the 2'- or α-OH) functionalities. Density functional theory (B3LYP/6-31G(d)) calculations confirm the energetic preference for these elimination channels and agree with the limited thermochemical data known for para- and ortho- benzoquinomethanes. The INC-mediated losses of the benzaldehydes from the [M + H](+) ions of the α-hydroxy-substituted 2-(2-phenylethyl)chromones correspond to a particularly facile (vinylogous) Grob fragmentation. The study may be viewed as a telling example of the diagnostic role of ion/neutral complexes as intermediates for the structural assignment of constitutional isomers by mass spectrometry.

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Section: + H] + [3 + H] + and [4 + H] + Namely Benzylic C-c Bond mentioning

confidence: 77%

Fragmentation of Protonated 2-(2-Phenylethyl)Chromones from Agarwood: The Diagnostic Role of Ion/Neutral Complexes as Reactive Intermediates

Yang

Xia

Jiang

et al. 2015

Eur J Mass Spectrom (Chichester)

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“…As shown in Figure , the substituents on the aromatic ring can be varied to create quinone analogs. The most common of these would include the quinomethanes (X = O, Y = CR 2 , Figure ) − or the quinodimethanes (xylylenes), − where both X and Y are carbon-centered substituents. However, essentially all multivalent atoms can be incorporated and in almost any combination.…”

Section: Introductionmentioning

confidence: 99%

“…However, essentially all multivalent atoms can be incorporated and in almost any combination. Whereas each variation will have unique properties, the common theme is that the ortho- and para-isomers will have stable, , Kekulé structures with closed-shell singlet electronic states, whereas the meta-isomers are higher-energy, non-Kekulé structures with high-spin electron coupling in the ground state, which is why meta -phenylene derivatives are commonly used as the basis for high-spin materials. − …”

Section: Introductionmentioning

confidence: 99%

Photoelectron Spectroscopy Study of Quinonimides

et al. 2017

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Structures and energetics of o-, m-, and p-quinonimide anions (OCHN) and quinoniminyl radicals have been investigated by using negative ion photoelectron spectroscopy. Modeling of the photoelectron spectrum of the ortho isomer shows that the ground state of the anion is a triplet, while the quinoniminyl radical has a doublet ground state with a doublet-quartet splitting of 35.5 kcal/mol. The para radical has doublet ground state, but a band for a quartet state is missing from the photoelectron spectrum indicating that the anion has a singlet ground state, in contrast to previously reported calculations. The theoretical modeling is revisited here, and it is shown that accurate predictions for the electronic structure of the para-quinonimide anion require both an accurate account of electron correlation and a sufficiently diffuse basis set. Electron affinities of o- and p-quinoniminyl radicals are measured to be 1.715 ± 0.010 and 1.675 ± 0.010 eV, respectively. The photoelectron spectrum of the m-quinonimide anion shows that the ion undergoes several different rearrangements, including a rearrangement to the energetically favorable para isomer. Such rearrangements preclude a meaningful analysis of the experimental spectrum.

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“…The procedure involves the formation of a ω-halosubstituted carbanion and then measuring the energy for halide elimination, as shown for the benzynes in eq . The CID approach for determining enthalpies of formation is very general and has been applied to the study of a wide range of reactive molecules, including carbenes, − carbynes, silylenes, diradicals, ,− and even triradicals. , In this work, we use energy-resolved CID to investigate the absolute enthalpies of formation of didehydropyridines, and to assess the relative energies of pyridyne isomers. We show that the nitrogen in the ring has little effect on the stability of the triple bond in 34DHP, but it significantly affects the stabilities and electronic structures of the 23DHP and 24DHP isomers.…”

Section: Introductionmentioning

confidence: 99%

Experimental Investigation of the Absolute Enthalpies of Formation of 2,3-, 2,4-, and 3,4-Pyridynes

Rau

Wenthold

2011

J. Phys. Chem. A

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The absolute enthalpies of formation of 3,4-, 2,3-, and/or 2,4-didehydropyridines (3,4-, 2,3- and 2,4-pyridynes) have been determined by using energy-resolved collision-induced dissociation of deprotonated 2- and 3-chloropyridines. Bracketing experiments find the gas-phase acidities of 2- and 3-chloropyridines to be 383 ± 2 and 378 ± 2 kcal/mol, respectively. Whereas deprotonation of 3-chloropyridine leads to formation of a single ion isomer, deprotonation of the 2-chloro isomer results in a nearly 60:40 mixture of regioisomers. The enthalpy of formation of 3,4-pyridyne is measured to be 121 ± 3 kcal/mol by using the chloride dissociation energy for deprotonated 3-chloropyridine. The structure of the product formed upon dissociation of the ion from 2-chloropyridine cannot be unequivocally assigned because of the isomeric mixture of reactant ions and the fact that the potential neutral products (2,3-pyridyne and 2,4-pyridyne) are predicted by high level spin-flip coupled-cluster calculations to be nearly the same in energy. Consequently, the enthalpies of formation for both neutral products are assigned to be 130 ± 3 kcal/mol. Comparison of the enthalpies of dehydrogenation of benzene and pyridine indicates that the nitrogen in the pyridine ring does not have any effect on the stability of the aryne triple bond in 3,4-pyridyne, destabilizes the aryne triple bond in 2,3-pyridyne, and stabilizes the 1,3-interaction in 2,4-pyridyne compared to that in m-benzyne. Natural bond order calculations show that the effects on the 2,3- and 2,4-pyridynes result from polarization of the electrons caused by interaction with the lone pair. The polarization in 2,4-pyridyne is stabilizing because it creates a 1,2-interaction between the nitrogen and dehydrocarbons that is stronger than the 1,3-interaction between the dehydrocarbons.

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Dissociation of chloride from ortho-, meta- and para-chloromethylphenoxides: The enthalpy of formation of meta-quinomethane

Cited by 12 publications

References 56 publications

Fragmentation of Protonated 2-(2-Phenylethyl)Chromones from Agarwood: The Diagnostic Role of Ion/Neutral Complexes as Reactive Intermediates

Fragmentation of Protonated 2-(2-Phenylethyl)Chromones from Agarwood: The Diagnostic Role of Ion/Neutral Complexes as Reactive Intermediates

Photoelectron Spectroscopy Study of Quinonimides

Experimental Investigation of the Absolute Enthalpies of Formation of 2,3-, 2,4-, and 3,4-Pyridynes

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