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首页> 外文期刊>Chemistry: A European journal >Organic Chemistry on Cold Molecular Films: Kinetic Stabilization of of S_N1 and S_N2 Intermediates in the Reactions of Ethanol and 2-Methylpropan-2-ol with Hydrogen Bromide
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Organic Chemistry on Cold Molecular Films: Kinetic Stabilization of of S_N1 and S_N2 Intermediates in the Reactions of Ethanol and 2-Methylpropan-2-ol with Hydrogen Bromide

机译：冷分子膜上的有机化学：乙醇和2-甲基丙-2-醇与溴化氢反应中S_N1和S_N2中间体的动力学稳定

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摘要

We prepared thin molecular films of ethanol and 2-methylpropan-2-ol on Ru(001) substrates at temperature of 100-150 K and examined their reactiviry toward HBr. The reaction intermediates and products formed at the surfaces were unambiguously identified by the techyniques of Cs~+ reactive ion scattering (RIS) and low-energy sputtering. The reaction on the ethanol surface produced protonated ethanol, which is stabilized on the surface and does not proceed to further reactions. On the 2-methylpropan-2-ol surface, protonated alcohol [(CH_3)_3COH_2~+] and carbocation [(CH_3)_3C~+] were formed with respective yield of 20 and 78%. Alkyl bromides, which are the final products of the corresponding reactions in liquid solvents, have extremely small yields on these suyrfaces (<0.3% for ethyl bromide and 2% for tert-butyl bromide). The results indicate that the reactions on frozen films are characterized by kinetic control, stabilization of ionic intermediates (protonated alcohols and tert-butyl cation), and effectife blocking of the charge recombination steps in S_N1 and S_N2 paths. The implication of theser findings for the molecular evolution process in interstellar medium is also discussed.
机译：我们在Ru（001）衬底上于100-150 K的温度下制备了乙醇和2-甲基丙-2-醇的分子薄膜，并研究了它们对HBr的活化性。通过Cs〜+反应离子散射（RIS）和低能溅射技术清楚地确定了在表面形成的反应中间体和产物。在乙醇表面上的反应产生质子化的乙醇，该质子化的乙醇在表面上稳定并且不进行进一步的反应。在2-甲基丙-2-醇表面上，形成了质子化的醇[（CH_3）_3COH_2 +]和碳阳离子[[CH_3）_3C〜+]，产率分别为20％和78％。烷基溴化物是液体溶剂中相应反应的最终产物，在这些表面上的收率极低（乙基溴<0.3％，叔丁基溴<2％）。结果表明，在冷冻膜上的反应具有动力学控制，离子中间体（质子化醇和叔丁基阳离子）稳定以及在S_N1和S_N2路径中影响电荷重组步骤的效果。还讨论了研究者发现对星际介质中分子进化过程的意义。

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