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The Adverse Effect of Benzannelation on the Aromaticity of Oxocinyl Anion: A Combined Experimental and Theoretical Study
Author(s) -
Kasmai Hamid S.,
Wang Xiaodong,
Doan HanhNhon,
Femia Josef F.,
Yablonsky Thad M.,
Read Mary E.,
Dutton David T.
Publication year - 2010
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.200900430
Subject(s) - chemistry , aromaticity , ring (chemistry) , moiety , benzene , delocalized electron , ab initio , ion , conjugate , electron delocalization , computational chemistry , stereochemistry , crystallography , molecule , organic chemistry , mathematical analysis , mathematics
Abstract A synthesis of 2 H ‐1‐benzoxocin from readily available compounds was accomplished. The potentially ‘aromatic’ π ‐excessive systems 2 H ‐1‐benzoxocinyl and 6 H ‐dibenz[ b , f ]oxocinyl anions were generated from their corresponding conjugate acid precursors 7c and 8 , respectively. It was found that 2 H ‐1‐benzoxocinide 3d lacks the type of π ‐frame stability associated with the parent 2 H ‐oxocinide 1d and that the dibenzo analog 5b is more unstable than 3d . Both 3d and 5b undergo rapid structural reorganization to form their corresponding stable isomeric anions. We were able to characterize the proton‐quenched products of these anions as the ring‐opened structures 15 and 18 , respectively. 1 H‐NMR and an ab initio calculation at the 6‐31g* level indicated that, unlike the ‘aromatic’ parent 2 H ‐oxocinide 1d and the aza analog 3c, 3d incorporates a non‐planar oxocinyl ring in which the negative charge is primarily localized on the pentadienyl moiety of the ring, but also partial delocalization of π ‐electron density onto the benzene ring occurs.