Goli Mohammad, Shahbazian Shant
Faculty of Chemistry, Shahid Beheshti University, G. C., Evin, P.O. Box 19395-4716, Tehran, 19839, Iran), Fax.
Chemistry. 2016 Feb 12;22(7):2525-31. doi: 10.1002/chem.201504318. Epub 2016 Jan 8.
Isotope substitutions are usually conceived to play a marginal role on the structure and bonding pattern of molecules. However, a recent study [Angew. Chem. Int. Ed. 2014, 53, 13706-13709; Angew. Chem. 2014, 126, 13925-13929] further demonstrates that upon replacing a proton with a positively charged muon, as the lightest radioisotope of hydrogen, radical changes in the nature of the structure and bonding of certain species may take place. The present report is a primary attempt to introduce another example of structural transformation on the basis of the malonaldehyde system. Accordingly, upon replacing the proton between the two oxygen atoms of malonaldehyde with the positively charged muon a serious structural transformation is observed. By using the ab initio nuclear-electronic orbital non-Born-Oppenheimer procedure, the nuclear configuration of the muon-substituted species is derived. The resulting nuclear configuration is much more similar to the transition state of the proton transfer in malonaldehyde rather than to the stable configuration of malonaldehyde. The comparison of the "atoms in molecules" (AIM) structure of the muon-substituted malonaldehyde and the AIM structure of the stable and the transition-state configurations of malonaldehyde also unequivocally demonstrates substantial similarities of the muon-substituted malonaldehyde to the transition state.
通常认为同位素取代对分子的结构和键合模式影响甚微。然而，最近的一项研究[《德国应用化学》国际版2014年，第53卷，13706 - 13709页；《德国应用化学》2014年，第126卷，13925 - 13929页]进一步表明，用带正电荷的μ子（作为氢的最轻放射性同位素）取代质子后，某些物种的结构和键合性质可能会发生根本性变化。本报告是基于丙二醛体系引入另一个结构转变例子的初步尝试。因此，在用带正电荷的μ子取代丙二醛两个氧原子之间的质子后，观察到了严重的结构转变。通过使用从头算核 - 电子轨道非玻恩 - 奥本海默程序，得出了μ子取代物种的核构型。所得的核构型与丙二醛中质子转移的过渡态更为相似，而非与丙二醛的稳定构型相似。对μ子取代丙二醛的“分子中的原子”（AIM）结构与丙二醛稳定构型和过渡态构型的AIM结构进行比较，也明确表明μ子取代丙二醛与过渡态存在显著相似性。
