56248-27-2Relevant academic research and scientific papers
β-deuterium kinetic isotope effects for identity processes: bromide ion substitution at 1-bromo-1-arylethanes and 2-bromooctane
Stein
, p. 1789 - 1796 (1994)
While deuterian kinetic isotope effects for solvolyses have been extensively studied, other nucleophilic substitutions have received less attention, and identity processes, that is, substitutions where the nucleophile and leaving group are the same, have rarely been examined. Identity reactions must pass through a truly symmetrical stage, a transition state or an intermediate, so that data will be of interest to both theoretical and experimental chemists. Values of kH/kD have been determined by polarimetry for bromide exchange-racemization at ArCHBrCH3/CD3 (Ar = C6H5, 4-Br- and 4-Me-C6H4, and 3,4,-dimethyl-C6H3) in acetone, acetonitrile, and nitromethane. Observed values are analogous to values seen in solvolyses. They range from 1.01 to 1.35 and, in some cases, increase markedly as the concentration of Bu4NBr decreases. Solvolyses are either first order or pseudo first order whereas plotting observed racemization rate versus [Bu4NBr] allows separation of first- and second-order components; those species giving more stable carbocations in the more dipolar solvents, the systems showing kH/kD variation with Br- concentration, alone show an appreciable first-order component. The second-order kH/kD ratio averages 1.062 ±-0.018 at temperatures ranging from 25 to 50°C for all substrates in the three solvents, very analogous to the values seen for racemization of 1,1,1-d3-2-bromooctane or solvolysis of ethyl substrates but considerably lower than the typical solvolysis values of 1.15-1.25 for secondary, and 1.35-1.5 for tertiary substrates. The first-order kH/kD values obtained are higher, 1.1-1.5. These and other results are discussed.
Solvolysis of 1-alkyl-1-chloro-1-(4-methyl)phenylmethanes. Nucleophilic solvent intervention and extended YBnCl scale
Liu, Kwang-Ting,Chang, Lih-Wie,Yu, Der-Gann,Chen, Pang-Shao,Fan, Ju-Ta
, p. 879 - 884 (2007/10/03)
The solvolysis of 1-alkyl-1-chloro-1-(4-methyl)phenylmethanes (4a-d) in aqueous acetone, aqueous ethanol, aqueous methanol and ethanol-trifluoroethanol was studied. Grunwald-Winstein-type correlation analysis using the YBnCl scale suggests significant nucleophilic solvent intervention in the case of 1-chloro-1-(4-methyl)phenylethane (4a). Increasing bulkiness of the 1-alkyl substituent from methyl (4a) to ethyl (4b), to isopropyl (4c) and to tert-butyl (4d) resulted in a gradual change to limiting SN1 mechanisms. The observed excellent linear correlations with YBnCl and the good solubility in high-water-containing binary solvents made 4d a suitable reference standard for deriving more YBnCl values. A positive azide salt effect was realized in the solvolysis of 4a but not 4d. A small decrease in the β-deuterium kinetic isotope effect from 4a to 1-chloro-1-(4-methoxyphenyl)propane (5) suggested the presence of additional stabilization of the benzylic cationic transition state. However, no relationship between k(CH3)/k(CD3) and the solvent effect was found. The superiority of employing the YBnCl scale over the combination of YCl and I scales in the mehanistic study was observed.
The Ei Reaction of Substituted threo- and erythro- 1-Phenylethyl Phenyl Sulfoxides
Yoshimura, Toshiaki,Tsukurimichi, Eiichi,Iizuka, Yukihiko,Mizuno, Hironobu,Isaji, Hiroshi,Shimasaki, Choichiro
, p. 1891 - 1899 (2007/10/02)
Substituted (RS,SR)-1-phenylethyl phenyl sulfoxides (threo) (XC6H4S(O)CH(CH3)C6H4Y) and some substituted (RR,SS)-sulfoxides (erythro) were prepared and kinetic investigation for the thermal decomposition was carried out at 80.0, 90.0, and 100.0 deg C in dioxane.Hammett plots for threo-XXC6H4S(O)CH(CH3)C6H5 gave positive ρ-values (ρx=0.60-0.64 at three temoeratures), while those for threo- and erythro-C6H5S(O)CH(CH3)C6H4Y showed V-shape lines with bottoms at the m-OCH3 substituent though the effects of the substituents were small.Meanwhile, large kinetic isotope effects for threo- and erythro-C6H5S(O)CH(O)CH(CH3)C6H4Y (Y=H, p-OMe, m-Cl) (kH/kD=4-6) were observed at all temperatures.The activation energies were in the range of 104-121 kJ mol-1 for all sulfoxides, while the activation entropies were relatively large (7-37 JK-1mol-1) and were correlated with Hammett ?-values to give small negative trend.Reactions of all erythro-isomers examined were 2-3 times faster than those of corresponding threo-isomers.From these results, it is suggested that the pyrolysis of 1-arylethyl aryl sulfoxides proceeds via a concerted mechanism in which the transition state is variable from an Ei'1-like to a conjugated one.In the latter transition state, conjugation of the phenyl group bearing the electron-withdrawing substituent with developing ?-bond electron acidifies the β-proton.
