Somani Ankit, Gupta Divanshu, Bettinger Holger F
Institut für Organische Chemie, Eberhard Karls Universität Tübingen, Auf der Morgenstelle 18, Tübingen 72076, Germany.
J Phys Chem A. 2024 Aug 22;128(33):6847-6852. doi: 10.1021/acs.jpca.4c02833. Epub 2024 Aug 12.
Cyclacenes, CH, consist of linearly fused benzene rings that are arranged to result in a closed nanohoop structure. Cyclacenes are thus the cyclic versions of acenes and have so far escaped synthesis. In order to estimate the tendency of []-cyclacenes (6 ≤ ≤ 20) to undergo dimerization, which is assumed to be a major pathway of degradation under oxygen-free conditions, we here report the energy of dimerization as computed by density functional theory using spin-restricted, spin-unrestricted, and thermally assisted-occupation (TAO) formalisms. It is found that the energy of dimerization increases with increasing size of but that this increase is not monotonic for the smaller members of the series. This is due to the combination of the cryptoannulenic effect and the inherent strain of the cyclacenes. The energy of dimerization of the largest member inspected, [20]-cyclacene, is -59.3 kcal/mol, while we expect it to converge to -46 kcal/mol for → ∞ based on comparison with data obtained for acenes.
环并苯（CH）由线性稠合的苯环组成，这些苯环排列形成封闭的纳米环结构。因此，环并苯是并苯的环状形式，迄今为止尚未成功合成。为了评估[ ]-环并苯（6≤ ≤20）发生二聚化的倾向（假定这是无氧条件下的主要降解途径），我们在此报告通过密度泛函理论使用自旋限制、自旋非限制和热辅助占据（TAO）形式计算得到的二聚化能量。结果发现，二聚化能量随 的增大而增加，但对于该系列中较小的成员，这种增加并非单调。这是由于隐环烯效应和环并苯固有张力共同作用的结果。所研究的最大成员[20]-环并苯的二聚化能量为-59.3千卡/摩尔，而基于与并苯获得的数据比较，我们预计当 → ∞时它将收敛至-46千卡/摩尔。
