N−H and α(C−H) Bond Dissociation Enthalpies of Aliphatic Amines
摘要:
Bond dissociation enthalpies (BIDES) of a large series of aliphatic amines (21) were measured by means of photoacoustic calorimetry. Despite the different structures studied in the primary, secondary, and tertiary amine series, the a(C-H) BIDES were found to be very similar for unconstrained amines with values very close to 91 kcal/mol. alphaC- and N-alkylation or introduction of an hydroxy group only slightly affect the BDEs, a fact in perfect agreement with calculations performed at different CBS levels. This demonstrates the predominance of the two-orbital-three-electron interaction involving the N and alphaC(.) orbitals. On the other hand, the N-H BIDE decreases when going from primary to secondary amines. This result is interpreted in term of a hyperconjugation in sigmaC-C bonds, which leads to a stabilization of the aminyl radical. For cyclized amines, the BIDES depend on the relative geometry of the singly occupied alphaC(.) orbital with respect to that of the N atom, disfavoring the two-orbital-three-electron interaction. However, such structures can exhibit through-bond interaction. For a crowded structure such as triisopropylamine, for which the alphaC(.) orbital is not coplanar with the nitrogen one, the relaxation of a strain energy allows the BIDE to be comparable to flexible structures.
Primary quantum yields of ketyl radicals in photoreduction by amines. Abstraction of hydrogen from nitrogen
作者:Shai Inbar、Henry Linschitz、Saul G. Cohen
DOI:10.1021/ja00524a034
日期:1980.2
photolysis studies of the primaryreaction of benzophenone triplet with aliphatic amines in benzene solution are reported. Quantum yield of formation of benzophenone ketyl radical was 0.9 - 1.0. Quantum yields for reduction of ketone also were determined for various amines, and the effects of tert-butyl alcohol on radical formation was investigated. Data indicated that H is not abstracted from -CH/sub
报告了二苯甲酮三联体与脂肪胺在苯溶液中的主要反应的激光闪光光解研究结果。二苯甲酮羰基自由基形成的量子产率为0.9-1.0。还测定了各种胺的酮还原的量子产率,并研究了叔丁醇对自由基形成的影响。数据表明 H 不是从 -CH/sub 3/ 中提取的,而是从 -NH/sub 2/ 中有效提取的。使用叔胺和仲胺观察到的非常高的量子产率被认为暗示了激基复合物的形成,但伯胺的较低量子产率有条件地归因于较高的电离电位。(BLM)
Radiolytic reductions and oxidations in dimethyl sulfoxide solutions: solvent effects on reactivity of halogen atom complexes
作者:M. Kumar、P. Neta
DOI:10.1021/j100187a032
日期:1992.4
Radiolysis of dimethyl sulfoxide (DMSO) solutions containing various additives was used to achieve clean one-electron reduction of oxidation of solutes. Pulse radiolysis of benzoquinone in DMSO solutions containing acetone and triethylamine permitted conversion of all primary radicals into reducing species. The total yield of reduction in the gamma-radiolysis of methyl viologen solutions was found to be 0.37-mu-mol/J. In the pulse radiolysis of TMPD and triphenylamine in aerated DMSO containing LiCl and/or CCl4, all the primary radicals were converted into oxidizing species and gave a maximum yield of 0.39-mu-mol/J. In the latter systems, oxidation was partly by halogen atom complexes. The reactivity of complexes of DMSO (DMSO.Cl, DMSO.Br) and of halide ions (Br2.-,I2.-) was examined for several organic compounds. DMSO.Cl oxidizes chlorpromazine, triphenylamine, and zinc porphyrin with rate constants of the order of 10(7)-10(8) M-1 s-1, and the rates increase upon addition of CH2Cl2 as well as upon addition of water and formamide. DMSO.Cl also reacts with olefins by addition of Cl to the double bond; the rate constants increase upon increasing the electron-donating properties of the substituents on the double bond. The rate constants for oxidation of chlorpromazine by Br2.- and I2.- increase by more than 2 orders of magnitude upon changing the solvent from DMSO gradually to water. The change was less with acetonitrile/water mixtures, and the difference is probably due to differences in ion solvation.
Absolute rate constants for the reactions of tert-butoxyl, tert-butylperoxyl, and benzophenone triplet with amines: the importance of a stereoelectronic effect
作者:D. Griller、J. A. Howard、P. R. Marriott、J. C. Scaiano
DOI:10.1021/ja00393a020
日期:1981.2
Hydrogen abstraction from amines: formation of aminyl vs. .alpha.-aminoalkyl radicals