ESR Proof of the Antiaromaticity of a Cyclopropenyl Radical

Abstract

C 0 M M U N I C AT1 0 N S pectation that even a cyclopropenyl radical with 3x-electrons has antiaromatic characterf5! By known methods[61 we have prepared di-tert-butyl-(3,5-ditert-butylpheny1)cyclopropenylium perchlorate ( 1 1 and from this by means of LiAIH4 1,3-di-tert-butyl-2-(3,5-di-tert-butyl-pheny1)cycloprepene (2). Photolysis of a solution of (2) in di-tert-butyl peroxide['] at -30°C affords a radical (3) whose Dedicated to Professor K. Dimroth on the occasion of his 65th birthday The simplest representatives of previously known antiaromatic[*} compounds are the 4x-electron systems cyclobutadiene and the cyclopropenyl anions bearing substituents that force the carbanion center to adopt a planar configuration. Calculations by the electron gas method[31 and MO calculations with consideration of overlap integralsc4] lead to the ex-Fig. 1. ESR spectrum of the di-tert-butyl-(3,5-d1-tert-butl.lphenyl)cyclopropenyl radical (3) in di-tert-butyl peroxide at -30°C.

Chemistry of β-(Acyloxy)alkyl and β-(Phosphatoxy)alkyl Radicals and Related Species: Radical and Radical Ionic Migrations and Fragmentations of Carbon−Oxygen Bonds

“…185,186 The 2,3-di-tert-butyl-1-(3,5-di-tert-butylphenyl)cyclopropenyl radical has a π-structure, presumably because of the extensive benzylic delocalization. 187 Thus, even these very crude models have significant localization of the π-electron density and this can only be accentuated by perturbations resulting from the inclusion of heteroatoms in the bonding framework. The indication is therefore clear: the transition states for the five-center-five-electron and three-center-three-electron migrations will have substantial localization of electron density, i.e., polarization as in 436 and 437.…”

Stationary Points on Potential Energy Surface of Cyclic C3H3 with Coupled-Cluster Approaches and Density Functional Theory

“…C 3 H 3 is an indispensable radical in reactions involving cyclic aromatic hydrocarbons, soot formation processes, and some combustion reactions. − For example, it is an important intermediate in forming the aromatic ring through recombination of two propargyl radicals. − , In addition, C 3 H 3 has been observed as one of the products in the C­( 3 P) + C 3 H 6 reaction in the atmospheres of Titan and giant planets as well as in the interstellar medium . Numerous experimental − and theoretical studies ,− have reported on this radical because of its significance. Previous studies ,,, show that several isomers of C 3 H 3 exist, including propargyl radical, cyclopropenyl radical (c-C 3 H 3 ), and others.…”

“…Experimental studies on the electron spin resonance (ESR) spectrum , and ionization potentials (IPs) of C 3 H 3 have been reported. On the other hand, the electronic structure of C 3 H 3 has also been investigated ,,− ,− ,− using various methods such as Hartree–Fock theory (HF), density functional theory (DFT), , coupled-cluster theory (CC), , configuration interaction (CI), multiconfiguration self-consistent field (MCSCF), and complete active space SCF (CASSCF). , Most of these studies focus on the aromaticity or antiaromaticity of C 3 H 3 , since aromaticity is closely related to its stability.…”

Numerical Estimation of the Pseudo-Jahn–Teller Effect Using Nonadiabatic Coupling Integrals in Monocyclic and Bicyclic Conjugated Molecules

“…Structural distortion or Jahn–Teller distortion along the e′ mode provides ethylene and allylic structures possessing C 2 v symmetry, where the ground states belong to A 2 and B 1 irreducible representations, respectively. These structures are connected by an in-plane distortion via a C s path on the pseudorotation surface. − Detailed results can be found in appropriate reports. − …”