Department of Chemistry, Texas A&M University, College Station, Texas 77842, USA.
J Am Chem Soc. 2011 Nov 2;133(43):17172-5. doi: 10.1021/ja2084288. Epub 2011 Oct 10.
The desymmetrizing effect of isotopic substitution on the geometry of otherwise symmetrical structures can be surprisingly large when there is anharmonic coupling between a desymmetrizing mode and modes whose zero-point energies are strongly isotope-dependent. This phenomenon is found to account for experimental observations that had been previously interpreted as implying asymmetry in bromonium ions and in hydrogen phthalate ions in aprotic solvents. The unlabeled structures are concluded to have the higher symmetry found in computed structures. Great care must be taken in applying isotopic perturbation as a test of asymmetry.
当非对称模式与零点能强烈依赖同位素的模式之间存在非谐耦合时，同位素取代对原本对称结构的非对称效应可能会非常大。这种现象被发现可以解释以前被解释为表明溴化铵离子和在非质子溶剂中的邻苯二甲酸氢离子不对称的实验观察结果。未经标记的结构被认为具有在计算结构中发现的更高对称性。在应用同位素扰动作为不对称性的测试时，必须非常小心。
