Some studies on the solvolysis of 1-chloro-1-alkyl cycloalkanes

Ranganayakulu, K.; Devi, M. Vasumathi; Rao, R. Balaji; Rajeswari, K.

doi:10.1139/v80-235

Cited by 9 publications

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“…Thus, the exocyclic double bond instability order 6 >> 7 > 5 was obtained from the solvolysis of I-alkyl cycloalkyl chlorides (20) and from the hydrolysis of lactams (21), whereas the oxygen exchange of cycloalkanones (22) gave an order of instability of 6 > 7 > 5 in acid and 6 > 5 = 7 in base.…”

Section: Discussionmentioning

confidence: 99%

Tautomeric equilibrium of cyclic β-ketoester enamines

Labelle¹,

Gravel²

1985

Can. J. Chem.

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This paper is dedicated to Professor Camille Sandorfy on the occasion of his 65th birthdayMARC LABELLE and DENIS GRAVEL. Can. J . Chem. 63, 1884Chem. 63, (1985.The conjugated-unconjugated tautomerism of P-ketoester enamines has been investigated. Enamines with different amine ring size, ketone ring size, and ester alkyl group have been prepared. Equilibrium ratios of the conjugated and unconjugated forms have been determined. A three-point rationalization is presented: (1) the relative instability of the conjugated form is due to a large steric interaction; (2) the ring size combination largely determines the equilibrium ratio because of energy differences between the resonance hybrid structures of the conjugated forms; (3) the ester alkyl group slightly affects the equilibrium ratio, through a difference in rotational freedom in the conjugated form. The degree of instability of double bonds exocyclic to 5-, and 6-, and 7-membered rings is discussed.MARC LABELLE et DENIS GRAVEL. Can. J. Chem. 63, 1884Chem. 63, (1985.L'equilibre tautomkrique des formes conjuguCes et dCconjuguees des Cnamines de p-cCtoesters a Ct C Ctudite. Plusieurs Cnamines de diverses grandeurs de cycle a I'amine et au cttoester et divers groupes alkyles I'ester ont Ct C prCparCes. Les proportions de formes conjuguCes et dCconjuguCes a l'equilibre sont rapportCes. Les rksultats sont expliquCs 21 partir de trois effets: (I) llinstabilitC relative des formes conjuguCes est due a une importante interaction stkrique; (2) les proportions des deux formes sont surtout controlCes par la grandeur des cycles impliquCs, en raison de differences d'Cnergie entre les structures hybrides de rksonance; (3) la nature du groupe alkyle de I'ester influence le rapport des deux formes a cause d'une diffCrence de IibertC de rotation dans la forme conjuguCe. Le degre d'instabilitt des doubles liens exocycliques a des cycles a 5, 6 et 7 chainons est discutC.In the course of our study on the scope and limitations of P-ketoester enamines in organic synthesis ( I ) , we became interested in investigating the factors which control the equilibrium between the conjugated and unconjugated forms in P-ketoester enamines (Scheme 1). An examination of the literature revealed that the presence, at equilibrium, of significant amounts of the unconjugated form is not a phenomenon limited to P-ketoester enamines (2-4) but has also been observed with P-ketoamide enamines (5-7), P-diketone enamines (4, 8, 9), P-ketosulfone enamines (lo), and P-ketothioamide enamines (7). The presence of this equilibrium has also been frequently noted in the results of enamine acylations (3, 5, 8, 10, 1 1) which often give some 1,3-diacylated product, resulting from acylation of the unconjugated form of the monoacylated product.The only systematic study dealing with the equilibrium between the conjugated and unconjugated forms in P-dicarbonyl enamines has been published by Colonna et al. (3). In this paper, the authors report the observed equilibrium proportions of conjugated and unconjugated forms ...

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Section: Discussionmentioning

confidence: 99%

Tautomeric equilibrium of cyclic β-ketoester enamines

Labelle¹,

Gravel²

1985

Can. J. Chem.

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“…The special behavior of the activation parameters in the heterolysis of bromide II originates apparently from the conformational effects weakly sensitive to the nature of solvent. The cyclohexyl substrate in the ground state exists in the chair form, and the carbocation arising in the transition state has a twistconformation D [3,19] thus governing the spatial requirements to the formation of the transition state.…”

Section: = K [Rbr]mentioning

confidence: 99%

Kinetics and Mechanism of Unimolecular Heterolysis of Framework Compounds: XVII. Solvation Effects in Dehydrobromination of tert-Butyl Bromide, 1-Bromo-1-Methylcyclohexane, and 2-Bromo-2-methyladamantane in Dipolar Aprotic Solvents

2005

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Dehydrobromination rate of tert-butyl bromide, 1-bromo-1-methylcyclohexane, and 2-bromo-2-methyladamantane grows with increasing polarity and dipole moment of solvents. No correlation was found between rate constants of the process and electrophilicity or ionizing power of the solvents. The observed solvation effects are due mainly to dispersion interactions. * For communication XXII, see [1].The dehydrobromination of tert-butyl bromide (I) [2], 1-bromo-1-methylcyclohexane (II) [3], and 2-bromo-2-methyladamantane (III) [4] follows the E1 mechanism. According to the modern data [5, 6] the unimolecular heterolysis (E1, S N 1, solvolysis) proceeds through successive formation of three types ion pairs: contact, space-separated, and solvent-separated.The rate of the unimolecular heterolysis is commonly governed by the polarity and electrophilicity of solvents [5,6]. These parameters determine also the ionizing power of the solvents. Therefore the decrease in the heterolysis rate of bromide IV in the solvent series (2) is caused mainly by the reduced electrophilic assistance from the solvent, and in going to the cyclohexanone additionally by the diminished polarity of the medium (the polarity of the other three solvents does not significantly differ). MeCN > g-butyrolactone > sulfolane > cyclohexanoneIt is presumed [9] that the electrophilic assistance to the heterolysis of bromide IV originates mainly from orientation and dipole-dipole interactions: in MeCN forms a linear quadrupole A involving a hydrogen bond, in the g-butyrolactone arises a cyclic quadrupole B, and in sulfolane possessing the highest value of the Gutman acceptor number AN [8] the molecule of the substrate coordinates with a solvent molecule providing a chargetransfer complex. In the least polar cyclohexanone the 5; 5 ; B 5 ; B 5 _6ROY_; B 5HDFWLRQ SURGXFWVIn the limiting stage the contact ion pair interacts with a cavity in the solvent which results from the fluctuation of the liquid density [7] (the cavities amount to ~10% of the liquid volume [8]). Thus a space-separated ion pair is formed that quickly transforms into the solvent-separated ion pair which in its turn rapidly affords the reaction products. The rate of these reactions is described by the first order kinetic equation (1). v = k [RBr]One of the previous communications from this series [9] contains data on the heterolysis kinetics of 2-bromo-2-phenyladamantane (IV) in MeCN, g-butyrolactone, sulfolane, and cyclohexanone (S N 1 reaction). In the mentioned solvent series the reaction rate decreased by three orders of magnitude because of diminishing of the ionizing power (E T [8]) and electrophilicity of the solvent. No correlation with the solvent polarity was observed.(1)(2)

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