Search

Abstract: In this work, we analyze the interactions of alkali metal cations with [6]‐ and [14]helicene and the cation mobility of therein. We found that the distortion of the carbon skeleton is the reason that some of the structures which are local minima for the smallest cations are not energetically stable for K+, Rb+, and Cs+. Also, the most favorable complexes are those where the cation is interacting with two rings forming a metallocene‐like structure, except for the largest cation Cs+, where the distortion provoked by the size of the cation destabilizes the complex. As far as mobility is concerned, the smallest cations, particularly Na+, are the ones that can move most efficiently. In [6]helicene, the mobility is limited by the capture of the cation forming the metallocene‐like structure. In larger helicenes, the energy barriers for the cation to move are similar both inside and outside the helix. However, complexes with the cation between two layers are more energetically favored so that the movement will be preferred in that region. The bonding analysis reveals that interactions with no less than 50 % of orbital contribution are taking place for the series of E+‐[6]helicene. Particularly, the complexes of Li+ show remarkable orbital character (72.5–81.6 %). [ABSTRACT FROM AUTHOR]

Extremely complicated isomerization mechanisms for the isomerization of the 2-norbornyl to 1,3-dimethylcyclopentenyl cation observed in the gas phase have been elucidated through Born-Oppenheimer molecular dynamics simulations and ab initio computations. These quantum chemical explorations revealed that there are two viable complex rearrangement pathways. The longer pathway involves consecutive ring-openings with the formation of acyclic allylic cation intermediates. Although these are avoided in the shorter pathway, both routes are feasible, because the energy barriers of their first steps differ by only 1.0 kcal/mol. Both pathways eventually converge to the same methylcyclohexenyl cation, which undergoes ring contraction and methyl and hydride shifts to yield the C7H11+ global minimum, namely the 1,3-dimethylcyclopentenyl cation. [ABSTRACT FROM AUTHOR]

The potential energy surface of C6Li6 was re-examined and a new non-symmetric global minimum was found. The new structure can be described as three C22− fragments strongly aggregated through lithium bridges. At high temperatures, fluxionality is perceived instead of dissociation. At 600 and 900 K, the BOMD simulations show that the lithium mobility is high, indicating that the cluster behaves in a liquid-like manner (BOMD=Born-Oppenheimer molecular dynamics). [ABSTRACT FROM AUTHOR]