Ab initio study and NBO analysis of configurational and conformational properties of cyclododeca-1,2,7,8-tetraene

Further, using NBO (Natural Bond Orbital) analysis, π and π∗ allenic bonding and antibonding orbital occupancies and also the deviations of σ and π bonding orbitals of allenic moieties were investigated. NBO results revealed that in the most stable form of meso configuration (meso-1-TBBC), the sum of the π∗ allenic antibonding orbital occupancies (Σπoccupancy∗) is greater than dl configuration ((±)-1-TB). In addition, NBO results indicated that in the (±)-1-TB conformer, the sum of σ and π allenic moieties bonding orbital deviations ( Σσdev+Σπdev), from their normal values, is lower than in the meso-1-TBBC form. All these facts could explain the relative more stability of (±)-1-TB conformer, as compared to the meso-1-TBBC form.