自由基反应 or 负离子反应

fantasticqhl

对于一个反应， 有两种反应机理的假设，自由基与负离子：

自由基：  A + radical  --> A0  + radical-H  ;    A0 +B0 --> A-B  (A0 与 B0 为自由基)

负离子： A   +   base  -->  A-  + base-H   ;    A-  +   B+   -->   A-B ( A- 与 B+ 分别是负正离子)

已经优化了反应物产物， 及自由基，负离子， 并且作了单点计算，也计算了反应焓。
从目前的结果来看， 负离子的机理更占优一些， 但是总感觉没有太大的说服力。
本想从反应势垒方面来比较， 但是自由基反应也没法算过渡态。

想请教一下各位， 我还能哪些方便来比较两种可能的反应机理呢？ 谢谢！

sobereva

自由基反应不代表没有过渡态，至少A + radical这一步应当是有的

fantasticqhl

sobereva 发表于 2016-9-30 20:17
自由基反应不代表没有过渡态，至少A + radical这一步应当是有的

谢谢SOB！那我试着去做一下过渡态的搜索。多谢多谢！

xylz6188

在这找到的，感觉解释得还不错。
https://www.researchgate.net/pos ... icals_on_Gauss_view
There are several ways to have "one more electron", depending on the atoms involved. For example, say the original system is neutral with charge=0 and multiplicity=1.
(1) If you only add 1 more electron to the system, it is not a neutral system anymore, with one more electron than the protons, so it carries a -1 charge; the new electron is not paired, so the multiplicity is 2.
(2) If the system lose one H+ (proton), the system is also not neutral anymore, also with one more electron than the protons, so it carries a -1 charge. However, no electron is lost, so all the electrons are still paired, and the multiplicity stays 1.
(3) If the system lose one H (radical), the system loses both a proton and an electron. So the number of electron and protons are the same and there is no net charge (0). However, one electron is lost so there is an unpaired electron, and the multiplicity is 2.