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Open AccessArticle

Substitution of H Atoms in Unsaturated (Vinyl-Type) Carbocations by Cl or O Atoms

by Evgenii S. Stoyanov, Irina Yu. Bagryanskaya and Irina V. Stoyanova

Int. J. Mol. Sci. 2023, 24(13), 10734; https://doi.org/10.3390/ijms241310734 - 27 Jun 2023

Cited by 1 | Viewed by 1615

Introduction of Cl and O atoms into C₄-vinyl carbocations was studied by X-ray diffraction analysis and IR spectroscopy. Chlorine atoms are weak electron acceptors in ordinary molecules but, within vinyl carbocations, manifest themselves as strong electron donors that accept a positive charge. The attachment of a Cl atom directly to a C=C bond leads to an increase in the e-density on it, exceeding that of the common double bond. The positive charge should be concentrated on the Cl atom, and weak δ⁻ may appear on the C=C bond. More distant attachment of the Cl atom, e.g., to a C atom adjacent to the C=C bond, has a weaker effect on it. If two Cl atoms are attached to the C_γ atom of the vinyl cation, as in Cl₂C_γC_δHC_αHCH₃, then the cation switches to the allyl type with two practically equivalent and almost uncharged C_γC_δC_α bonds. When such a strong nucleophile as the O atom is introduced into the carbocation, a protonated ester molecule with a C–O(H⁺)–C group and a C=C bond forms. Nonetheless, in the future, there is still a possibility of obtaining carbocations with a non-protonated C–O–C group. Full article

(This article belongs to the Special Issue Carbocations: Properties and Reactivity)

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14 pages, 5325 KB

Open AccessArticle

Interaction of Vinyl-Type Carbocations, C₃H₅⁺ and C₄H₇⁺ with Molecules of Water, Alcohols, and Acetone

by Evgenii S. Stoyanov, Irina Yu. Bagryanskaya and Irina V. Stoyanova

Molecules 2023, 28(3), 1146; https://doi.org/10.3390/molecules28031146 - 23 Jan 2023

Cited by 2 | Viewed by 2358

Abstract

X-ray diffraction analysis and IR spectroscopy were used to study the products of the interaction of vinyl cations C₃H₅⁺ and C₄H₇⁺ (Cat⁺) (as salts of carborane anion CHB₁₁Cl₁₁⁻) with basic molecules of water, alcohols, and acetone that can crystallize from solutions in dichloromethane and C₆HF₅. Interaction with water, as content increased, proceeded via three-stages. (1) adduct Cat⁺·OH₂ forms in which H₂O binds (through the O atom) to the C=C⁺ bond of the cation with the same strength as seen in the binding to Na in Na(H₂O)₆⁺. (2) H⁺ is transferred from cation Cat⁺·OH₂ to a water molecule forming H₃O⁺ and alcohol molecules (L) having the CH=CHOH entity. The O- atom of alcohols is attached to the H atom of the C=C⁺-H moiety of Cat⁺ thereby forming a very strong asymmetric H–bond, (C=)C⁺-H⋅⋅⋅O. (3) Finally all vinyl cations are converted into alcohol molecule L and H₃O⁺ cations, yielding proton disolvates L-H⁺-L with a symmetric very strong H-bond. When an acetone molecule (Ac) interacts with Cat⁺, H⁺ is transferred to Ac giving rise to a reactive carbene and proton disolvate Ac-H⁺-Ac. Thus, the alleged high reactivity of vinyl cations seems to be an exaggeration. Full article

(This article belongs to the Special Issue Chemical Bond and Intermolecular Interactions)

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7 pages, 1354 KB

Open AccessCommunication

Spontaneous Transition of Alkyl Carbocations to Unsaturated Vinyl-Type Carbocations in Organic Solutions

by Evgenii S. Stoyanov and Irina V. Stoyanova

Int. J. Mol. Sci. 2023, 24(2), 1802; https://doi.org/10.3390/ijms24021802 - 16 Jan 2023

Cited by 2 | Viewed by 2683

Abstract

It was found that alkyl carbocations, when their salts are dissolved in common organochlorine solvents, decompose to unsaturated vinyl-type carbocations that are stabler in solutions. This is a convenient method for obtaining salts of vinyl cations and their solutions for further research. Full article

(This article belongs to the Special Issue Structure, Energy and Dynamics of Molecular Interactions)

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21 pages, 7184 KB

Open AccessArticle

The Chloronium Cation [(C₂H₃)₂Cl⁺] and Unsaturated C₄-Carbocations with C=C and C≡C Bonds in Their Solid Salts and in Solutions: An H¹/C¹³ NMR and Infrared Spectroscopic Study

by Evgenii S. Stoyanov and Irina V. Stoyanova

Int. J. Mol. Sci. 2022, 23(16), 9111; https://doi.org/10.3390/ijms23169111 - 14 Aug 2022

Cited by 7 | Viewed by 3283

Abstract

Solid salts of the divinyl chloronium (C₂H₃)₂Cl⁺ cation (I) and unsaturated C₄H₆Cl⁺ and C₄H₇⁺ carbocations with the highly stable CHB₁₁Hal₁₁⁻ anion [...] Read more.

Solid salts of the divinyl chloronium (C₂H₃)₂Cl⁺ cation (I) and unsaturated C₄H₆Cl⁺ and C₄H₇⁺ carbocations with the highly stable CHB₁₁Hal₁₁⁻ anion (Hal=F, Cl) were obtained for the first time. At 120 °C, the salt of the chloronium cation decomposes, yielding a salt of the C₄H₅⁺ cation. This thermally stable (up to 200 °C) carbocation is methyl propargyl, CH≡C-C⁺-H-CH₃ (VI), which, according to quantum chemical calculations, should be energetically much less favorable than other isomers of the C₄H₇⁺ cations. Cation VI readily attaches HCl to the formal triple C≡C bond to form the CHCl=CH-C⁺H-CH₃ cation (VII). In infrared spectra of cations I, VI, and VII, frequencies of C=C and C≡C stretches are significantly lower than those predicted by calculations (by 400–500 cm⁻¹). Infrared and ¹H/¹³C magic-angle spinning NMR spectra of solid salts of cations I and VI and high-resolution ¹H/¹³C NMR spectra of VII in solution in SO₂ClF were interpreted. On the basis of the spectroscopic data, the charge and electron density distribution in the cations are discussed. Full article

(This article belongs to the Special Issue Structure, Energy and Dynamics of Molecular Interactions)

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15 pages, 273 KB

Open AccessArticle

Kinetics and Mechanism of Acetoxymercuration and Acid-Catalysed Hydration of α-Alkylstyrenes

by Jan Svoboda, Monika Pelcová, Taťjana Nevěčná and Oldřich Pytela

Int. J. Mol. Sci. 2005, 6(1), 30-44; https://doi.org/10.3390/i6010030 - 31 Jan 2005

Cited by 2 | Viewed by 8425

Abstract

Nine α-alkylstyrenes carrying the following substituents have been synthesised: methyl, ethyl, propyl, butyl, pentyl, isobutyl, isopropyl, sec-butyl and tert-butyl. Kinetics has been measured for the reaction of these compounds with mercuric acetate in anhydrous acetic acid at 25 °C. The rate constants are very sensitive to inductive effects (ρ_I = –49.5 in AISE theory) and steric effects (ψ = –1.59 according to Charton). These results support the presumed existence of an intermediate with an asymmetrically bound acetylmercuric cation to carbon atoms of the vinyl group of styrene. The kinetics of an acid-catalysed hydration of the above-mentioned α-alkylstyrenes were also measured in aqueous sulphuric acid at 25 °C. The derivatives exhibited kinetically a consecutive isomerisation reaction giving the more stable substituted styrenes. The values of the slope m^‡m* of the dependence upon the excess acidity function (X) were evaluated, and exceptionally low values were found for the butyl and pentyl substituents (1.02 and 0.73, respectively), while on the other hand tert-butyl showed an exceptionally high value (3.28). On the basis of the facts, a mechanism has been suggested for the acid-catalysed hydration, involving the reaction of a relatively stable and sterically hindered carbocation with water as the rate-limiting step of the reaction. Full article

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