- The Elimination Kinetics of Methoxyalkyl Chlorides in the Gas Phase. Evidence for Neighboring Group Participation
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The rates of elimination of 3-methoxy-1-chloropropane and 4-methoxy-1-chlorobutane have been determined in a seasoned, static reaction vessel over the temperature range of 410-490 deg C and the pressure range of 56-181 torr.The reactions are homogeneous and unimolecular, follow a first-order rate low, and are invariant to the presence of a twofold or greater excess of the radical chain inhibitor toluene.The overall rate coefficients are given by the following Arrhenius equations: for 3-methoxy-1-chloropropane, logk1(s-1)=(12.92+/-0.48)-(226.0+/-6.8) kJ mol-1(2.303RT)-1; for 4-methoxy-1-chlorobutane, logk1(s-1)=(12. 9+/-0.26)-(218.1+/-3.5) kJ mol-1(2.303RT)-1.The CH3O group in 4-methoxy-1-chlorobutane has been found to assist anchimerically the elimination reaction, where dehydrochlorination and tetrahydrofuran formation arise from an intimate ion pair type of mechanism.The partial rates for these parallel eliminations have been determined and reported.Participation of the CH3O in 3-methoxy-1-chloropropane is barely detected.The present results give further evidence of intimate ion pair mechanism through neighboring group perticipation in the gas-phase elimination of certain types of organic molecules.
- Chuchani, Gabriel,Martin, Ignacio
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p. 431 - 433
(2007/10/02)
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- Deamination Reactions, 41. Reactions of Aliphatic Diazonium Ions and Carbocations with Ethers
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Aliphatic diazonium ions and carbocations were generated by deacylation of appropriate nitrosoureas (1, 5, 9) in alcohol-ether mixtures or in 2-alkoxyethanols.Ethers were generally inferior to alcohols in capturing cationic intermediates.Formation of trialkyloxonium ions led to alkyl exchange or ring opening.The observed reactivity orders were n-butyl > isobutyl for the diazonium ions, allyl > sec-butyl > tert-butyl for the carbocations, methoxy > ethoxy and oxirane > oxetane > tetrahydrofuran for the ethers, indicating the predominance of steric effects.Neighboring group participation in 4-methoxy-1-butanediazonium ions (58) and 4,5-epoxy-1-pentanediazonium ions (74) was detectable but inefficient ( 20percent of cyclic oxonium ions).
- Kirmse, Wolfgang,Jansen, Ulrich
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p. 2607 - 2625
(2007/10/02)
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- OXYGEN YLIDES-II. PHOTOCHEMICAL AND RHODIUM-CATALYZED REACTIONS OF DIAZOMETHANE WITH (S)-2-METHYLOXETANE
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Photolysis of diazomethane in (S)-2-methyloxetane gives 2- and 3-methyltetrahydrofuran (1:3.2), the latter being formed with 21 percent net retention of configuration.In contrast, rhodium acetate catalysis yields racemic 3-methyltetrahydrofuran exclusively.
- Kirmse, Wolfgang,Chiem, Pham Van
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p. 197 - 200
(2007/10/02)
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- ETUDE DES INTERACTIONS ENTRE FONCTIONS ALCOOL ET AMINE: EVOLUTION THERMIQUE D'HYDROXYDES ET DE SELS D'ω-TRIALKYLAMMONIO ALCANOLS-1
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The thermolysis of ω-hydroxyalkyltrialkylammonium hydroxides (Φ=4-8) was investigated: Elimination to alkenol competes with substitution to amino alcohol; the hydroxy group can be alkylated into aliphatic ethers by an intermolecular process; the intramolecular cyclization into cyclic ethers is important only when ω=4.Substitution reaction in amino alcohols is the main pathway for the thermolysis of ω-hydroxyalkyltrimethylammonium acetates (ω=5,6) and chloride (ω=6).
- Barbry, Didier,Hasiak, Bruno
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p. 1734 - 1744
(2007/10/02)
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