The Glidewell–Lloyd rule explains the local aromaticity and the relative stability of benzoborepin isomers

Abstract

We examine the aromaticity of four benzoborepin isomers using magnetic, geometric, and delocalization criteria. We observe a trend in which the six-membered ring (6MR) exhibits higher aromaticity for isomers 1 and 2, while the seven-membered ring (7MR) exhibits a more pronounced aromatic character in isomers 3 and 4. Our CCSD(T)-level calculations demonstrate that isomers 1 and 2 are more stable (in that order), consistent with their higher aromaticity than isomers 3 and 4. The results of the three criteria mentioned above show a preference for forming the 6MR over the 7MR in the more stable isomers. Additionally, the 6MR in 1 shows a higher aromaticity when compared to 2 which explains its greater stability. For this reason, we conclude that the Glidewell–Lloyd rule governs aromaticity and relative stability in benzoborepines.