Formation of the oxonium phenol ion in the stepwise hydration of the phenyl cation in the gas phase

Elroby, Shaaban A.; Aziz, Saadullah G.; Hilal, Rifaat; Attah, Isaac K.; Platt, Sean P.; El‐Shall, M. Samy

doi:10.1016/j.molliq.2020.114541

Cited by 4 publications

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“…The strong NH + ···OH 2 (H 2 O) n −1 hydrogen bonds with water molecules can further stabilize the distonic structures of the hydrated ions. A similar situation was observed in the sequential hydration of the phenyl cation (C 6 H 5 + ), where hydrated oxonium phenol (C 6 H 5 OH 2 + (H 2 O) n ) cluster ions were suggested to be involved . These clusters (C 6 H 5 OH 2 + (H 2 O) n ) represent the formation of an externally hydrated ion with stepwise hydration energies ranging from 25.9 kcal/mol for n = 1 to 11.5 kcal/mol for n = 5, significantly higher than those of the weak CH δ+ ···O hydrogen bonds in the hydration of the benzene radical cation …”

Section: Introductionsupporting

confidence: 54%

Water-Assisted Proton Transfer in the Sequential Hydration of Benzonitrile Radical Cation C₆H₅CN^•+(H₂O)_n: Transition to Hydrated Distonic Cation ^•C₆H₄CNH⁺(H₂O)_n with n ≥ 4

et al. 2022

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The stepwise hydration of the benzonitrile•+ radical cation with one–seven H2O molecules was investigated experimentally and computationally with density functional theory in C6H5CN•+(H2O) n clusters. The stepwise binding energies (ΔH n–1,n °) were determined by equilibrium measurements for C6H5CN•+(H2O) and for •C6H4CNH+(H2O) n with n = 5, 6, and 7 to be 8.8 and 11.3, 11.0, and 10.0 kcal/mol, respectively. The populations of n = 2 and 3 of the C6H5CN•+(H2O) n clusters were observed only in trace abundance due to fast depletion processes leading to the formation of the hydrated distonic cations •C6H4CNH+(H2O) n with n = 4–7. The observed transition occurs between conventional radical cations hydrated on the ring in C6H5CN•+(H2O) n clusters with n = 1–3 and the protonated radical •C6H4CNH+ (distonic ion) formed by a proton transfer to the CN nitrogen and ionic hydrogen bonding to water molecules in •C6H4CNH+(H2O) n clusters with n = 4–7. The measured binding energy of the hydrated ion C6H5CN•+(H2O) (8.8 kcal/mol) is similar to that of the hydrated benzene radical cation (8.5 kcal/mol) that involves a relatively weak CHδ+···O hydrogen bonding interaction. Also, the measured binding energies of the •C6H4CNH+(H2O) n clusters with n = 5–7 are similar to those of the protonated benzonitrile (methanol) n clusters [C6H5CNH+(CH3OH) n , n = 5–7] that involve CNH+···O ionic hydrogen bonds. The proton shift from the para-•C ring carbon to the nitrogen of the benzonitrile radical cation is endothermic without solvent but thermoneutral for n = 1 and exothermic for n = 2–4 in C6H5CN•+(H2O) n clusters to form the distonic •C6H4CN···H+(OH2) n clusters. The distonic clusters •C6H4CN···H+(OH2) n constitute a new class of structures in radical ion/solvent clusters.

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Section: Introductionsupporting

confidence: 54%

Water-Assisted Proton Transfer in the Sequential Hydration of Benzonitrile Radical Cation C₆H₅CN^•+(H₂O)_n: Transition to Hydrated Distonic Cation ^•C₆H₄CNH⁺(H₂O)_n with n ≥ 4

et al. 2022

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“…The formation of oxonium ion (Ph‐OH 2 + ) in the stepwise hydration of the phenol cation (Ph‐OH +• ) was recently experimentally observed by Elroby et al [41] in the gas phase. The unsubstituted H‐Ph‐OH 2 + are thermally stable up to nearly 575 K while the hydrated phenyl cation dissociates by the loss of water at temperatures below 400 K. The mutual comparison of reaction Gibbs energies –∆ r G 2 collected in Table 2 indicate that the reaction of phenol and proton in gas phase leading to the formation of oxonium species have very strong exothermic character, that is, −731 kJ mol −1 .…”

Section: Resultsmentioning

confidence: 96%

On energetics of proton and electron transfer of selected phenol derivatives: Theoretical investigation of radical and oxonium cations

Kováčová

Michalík

Lukeš

2023

Int J of Quantum Chemistry

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In this paper, the systematic theoretical study of phenol and 36 compounds representing various ortho, meta and para‐substituted (R‐PhOH) phenols is presented. The hydroxyl group acidity is a characteristic feature of phenol which can be modified using substitution of phenyl ring. The proton‐coupled electron transfer was investigated for parent neutral phenols, R‐PhOH, their cation radicals, R‐PhOH+•, and oxonium cations, R‐PhOH2+. Density functional theory calculations were combined with solvent continuum model for water and dimethyl sulfoxide environment. For aqueous solution, the Pourbaix diagrams (electrochemical potential vs. pH) were constructed from the theoretically predicted acidity constants and electrochemical standard potentials. From the thermodynamic point of view, the obtained theoretical results allow the estimation of the thermodynamically preferred process and alternative reaction pathways of phenolic derivatives in very acidic media.

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“…DFT calculations indicated that a high electric field (∼10 7 MV/cm) ), especially when it remains protonated as oxonium phenol ion (Figure 5c), resulting in Ph + . 42,43 Based on all of the above evidence, we propose a viable model for the aromatic S N 1 reaction of phenols at the air− water interface (Figure 5d). The high electric field at this interface possibly causes the spontaneous transformation of phenols to aryl carbocations by the heterolytic fission of the Csp 2 −OH bond, which is further assisted by the protonation of the phenolic −OH group pointing toward the surface.…”

mentioning

confidence: 94%

“…A molecular dynamics (MD) simulation revealed that phenols in microdroplets are surface active and prefer to exist at the air–water interface (Figures a and S36) − in such that the aromatic ring points toward the air side and the −OH group is immersed in water (Figure S37), as shown diagrammatically in Figure b. DFT calculations indicated that a high electric field (∼10 7 MV/cm) could weaken and facilitate the cleaving of the phenolic C–O bond (Figures S38), especially when it remains protonated as oxonium phenol ion (Figure c), resulting in Ph + . , …”

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confidence: 99%

Spontaneous Generation of Aryl Carbocations from Phenols in Aqueous Microdroplets: Aromatic S_N1 Reactions at the Air–Water Interface

et al. 2023

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Although phenol is stable in bulk water, we report an exceptional phenomenon in which phenol is spontaneously transformed into a phenyl carbocation (Ph+) in water microdroplets. The high electric field at the air–water interface is proposed to break the phenolic Csp2–OH bond, forming Ph+, which remains in equilibrium with phenol as deciphered by mass spectrometry. We detected up to 70% conversion of phenol to Ph+ in aqueous microdroplets, although catalyst-free activation of the phenolic Csp2–OH bond is challenging. This transformation is well tolerated by a wide range of electron-donating and -withdrawing substituents in phenolic compounds. The Ph+ in water microdroplets could be reacted with various nucleophiles (amine, pyridine, azide, thiol, carboxylic acid, alcohol, and 18O-water), yielding the ipso-substitution products of phenol through an aromatic SN1 mechanism. Despite the fleeting life of Ph+ in the bulk, this study demonstrates its unusual stability at the aqueous microdroplet surface, enabling its detection and transformation.

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Formation of the oxonium phenol ion in the stepwise hydration of the phenyl cation in the gas phase

Cited by 4 publications

References 36 publications

Water-Assisted Proton Transfer in the Sequential Hydration of Benzonitrile Radical Cation C₆H₅CN^•+(H₂O)_n: Transition to Hydrated Distonic Cation ^•C₆H₄CNH⁺(H₂O)_n with n ≥ 4

Water-Assisted Proton Transfer in the Sequential Hydration of Benzonitrile Radical Cation C₆H₅CN^•+(H₂O)_n: Transition to Hydrated Distonic Cation ^•C₆H₄CNH⁺(H₂O)_n with n ≥ 4

On energetics of proton and electron transfer of selected phenol derivatives: Theoretical investigation of radical and oxonium cations

Spontaneous Generation of Aryl Carbocations from Phenols in Aqueous Microdroplets: Aromatic S_N1 Reactions at the Air–Water Interface

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Formation of the oxonium phenol ion in the stepwise hydration of the phenyl cation in the gas phase

Cited by 4 publications

References 36 publications

Water-Assisted Proton Transfer in the Sequential Hydration of Benzonitrile Radical Cation C6H5CN•+(H2O)n: Transition to Hydrated Distonic Cation •C6H4CNH+(H2O)n with n ≥ 4

Water-Assisted Proton Transfer in the Sequential Hydration of Benzonitrile Radical Cation C6H5CN•+(H2O)n: Transition to Hydrated Distonic Cation •C6H4CNH+(H2O)n with n ≥ 4

On energetics of proton and electron transfer of selected phenol derivatives: Theoretical investigation of radical and oxonium cations

Spontaneous Generation of Aryl Carbocations from Phenols in Aqueous Microdroplets: Aromatic SN1 Reactions at the Air–Water Interface

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Water-Assisted Proton Transfer in the Sequential Hydration of Benzonitrile Radical Cation C₆H₅CN^•+(H₂O)_n: Transition to Hydrated Distonic Cation ^•C₆H₄CNH⁺(H₂O)_n with n ≥ 4

Water-Assisted Proton Transfer in the Sequential Hydration of Benzonitrile Radical Cation C₆H₅CN^•+(H₂O)_n: Transition to Hydrated Distonic Cation ^•C₆H₄CNH⁺(H₂O)_n with n ≥ 4

Spontaneous Generation of Aryl Carbocations from Phenols in Aqueous Microdroplets: Aromatic S_N1 Reactions at the Air–Water Interface