The Protoadamantane Radical Cation

Abstract

Keywords: C-H activation / Density functional calculations / Electron transfer / Electrophilic additions / Radical ions DFT (B3LYP) and MP2 computations with a 6-31G* basis set show that a unique protoadamantane radical cation (1 ·+ ) structure with an elongated, half-broken C 6 −H bond prevails both in the gas phase and in solution. This is in agreement with the observed regioselectivity of the single electrontransfer oxidation of protoadamantane (1) with photoexcited 1,2,4,5-tetracyanobenzene, which only gives 5-(6-protoadamantyl)-1,2,4-tricyanobenzene (5), for which the X-ray crys-

Hydrocarbon σ‐radical cations

“…In complete agreement with the above computations, the SET oxidation of 20 in presence of photoexcited TCB in solution gave 21 as the only product (Scheme ), as a result of hydrogen loss from the C 6 H position of 20 •+ 138…”

“…Having a nondegenerate and delocalized HOMO (Figure 9), C 1 ‐symmetric protoadamantane ( 20 ) is Jahn–Teller inactive. Despite a number of possibilities for the formation of different radical cations with elongated tert CH bonds, optimizations at different levels [BLYP, B3LYP, and MP2/6–31G(d)] of 20 •+ lead to a single structure with one elongated C 6 H bond (Figure 8; for the numbering of carbons, see Scheme ) 138…”

Comparative theoretical and experimental analysis of hydrocarbon σ-radical cations

“…We previously studied the structure and transformations of radical cations derived from adamantane and its alkyl derivatives [14], cubane [15], protoadamantane [16], homoadamantane [17], propellanes [18], and rotanes [19] in terms of the density functional theory (DFT) with the use of popular B3LYP functional. Although in some cases good correlations between the calculated (B3LYP) and experimental data were observed, in particular for diamondoids [20], the problem related to applicability of various theoretical approaches to hydrocarbon σ-radical cations and improvement of their quality remains important.…”

Carbon‐rich Compounds: Computational Considerations

“…With the structures depicted in Scheme 8.11, one can therefore predict the CaH bond that will be broken from the optimized geometry of the respective diamondoid radical cation. This subsequent deprotonation usually produces the respective hydrocarbon radicals much more selectively than through direct radical H-abstractions [130,137,139]. Although the higher diamondoids are only slightly strained, they display remarkably low adiabatic IPs (177-184 kcal mol À1 ) hence, SET oxidations with conventional single-electron chemical oxidants are predicted to be practically valuable.…”

“…Despite common suspicions about the selectivities of reactions involving hydrocarbon radical cations, these reactions are often the most selective relative to cationic and radical transformations [130,136,137]. Single-electron transfer (SET) oxidations of hydrocarbons to radical cations require strong oxidants as the oxidation potentials of saturated hydrocarbons are rather high.…”