Exceptional design of super/hyperbases based on spiro‐alleneic structures in gas phase: A density functional theory study

Abstract

In this investigation, some of the designed spiro-alleneic derivatives with variety electron-donating substituents have been studied by B3LYP/6-311 + G(d,p) level of theory to assess their potential as strong hyperbases and superbases.The results showed that the protonation at alleneic C (sp) site gives 14 novel neutral organic bases with significant proton affinities (PAs) = 252.83-318.44 kcalÁmol À1 , in which six of them are hyperbases and the rest of them are superbases. The PAs of designed spiro-alleneic derivatives were improved by substitution of electron-releasing groups on the molecular structure. Two indices of aromaticity, nucleus-independent chemical shift (NICS) and harmonic oscillator model of aromaticity (HOMA), were also applied for the explanation of basicity of three spiro-alleneic derivatives, which indicates that cyclopropene and cycloheptatriene rings on some of the designed structures turn aromatic upon protonation of alleneic central carbon atom.