Abstract
The electronic and geometric structures of benzocyclobutadiene ( 1), biphenylene ( 2) and their protonated forms are studied by the ab initio HF 6-31G * and MP2(fc)/6-31G * //HF/6-31G * methods. It is shown that β-protonated species are more stable in both cases indicating greater susceptibility of the β-positions towards electrophilic substitutions. This finding is rationalized by the lower π-electronic energy estimated by the valence bond resonance structures and a decreased antagonism between σ- and π-electrons in β-Wheland intermediates. The inherent generalized strain energies in the parent compounds ( 1) and ( 2) are estimated by homodesmic reactions. It is found that the intrinsic destabilization energy is ≈ 8 kcal mol −1 higher in 1, which is interpreted as the inability of the peripheral double bond to escape the cyclobutadiene antiboding pattern in an efficient way. The semiempirical AMI calculations give correct qualitative results, but fail at the quantitative level.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.