Ring-opening of some radicals containing the cyclopropylmethyl system
作者:Athelstan L. J. Beckwith、Graeme Moad
DOI:10.1039/p29800001473
日期:——
Mono- and bi-cyclic radicals containing the cyclopropylmethyl system are readily generated by interaction of the appropriate halides with triphenyl- or tributyl-stannane. Each radical studied underwent ring-opening by fission of the more substituted βγ-bond. In the case of the secondary radical (12b) the new double bond was formed preferentially in the trans-configuration. Rate constants, which cannot
通过适当的卤化物与三苯基或三丁基锡烷的相互作用,容易产生含有环丙基甲基系统的单环和双环基团。每个被研究的基团都通过更取代的βγ键的裂变而开环。在第二自由基(12b)的情况下,优先以反式构型形成新的双键。无法通过此方法高精度确定的速率常数在1×10 7 –3×10 8 s –1的范围内在25°C下。当通过流动方法在esr腔中产生时,α-羟基环丙基甲基自由基经历β裂变,随后进行1,5-氢原子转移以提供烯氧基。与非极性溶剂相比,后者在水中的反应更慢。刚性羟基降三环基自由基(43)可能会由于过渡态的偶极性质而优先发生取代度较低的βγ键的裂变。
Homolytic displacement at carbon centres
作者:Michael D. Johnson、Gary M. Lampman、Roger W. Koops、B. Das Gupta
DOI:10.1016/0022-328x(87)80163-8
日期:1987.6
radical at the terminal unsaturated carbon of the organic ligand, with displacement of cobaloxime(II). In contrast, N-bromoacetamide and several other N-halogenoimides react regiospecifically to give the cyclopropylcarbinyl halide or the rearranged allyl halide by a process in which a halogen-containing free radical species attacks the terminal unsaturated carbon of the organocobaloxime.
β-deuterium isotope effect usually observed for a CD3-group (1·30–1·40). The results are discussed in terms of transition states and carbonium ion intermediates related to bicylobutonium ions (V). The reduced magnitude of the secondary deuterium isotopeeffects is correlated with small methyl- and phenyl-substitution rate effects. The hypothesis is advanced that secondary β-deuterium isotopeeffects might
制备了甲基和甲基-d 3取代的环丙基羰基和环丁基衍生物(I–IV),并测量了它们的溶剂分解速率。已经发现,环丙基羰基衍生物(I,III)的环上的甲基取代比类似的苯基取代产生较小但明显更大的速率增强。甲基氘化对溶剂分解速率没有显着影响。羰基(IV)处的甲基取代将溶剂分解速率提高了2. 10 3至4. 10 3倍,这比通常观察到的要小(10 4 –10 6)。1-甲基-d 3-环丁基甲磺酸盐(IIb-D)和1-环丙基乙基-2-d 3在96%乙醇中溶解后,氯化物(IVc-D)的显示仅为四分之一(k H / k D = 1·09)。对于CD 3-组(1·30-1·40),通常观察到动力学的继发性β-氘同位素同位素效应的一半(k H / k D = 1·19 )。根据过渡态和与双环丁鎓离子(V)有关的碳鎓离子中间体讨论了结果。次级氘同位素效应的降低幅度与较小的甲基和苯基取代速率效应相关。提出了这样的