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On the π‐Electron Distribution in Biphenylene Analogues
Author(s) -
Andres Werner,
Günther Harald,
Günther MariaEugenia,
Hausmann Heike,
Jikeli Günther,
von Puttkamer Henning,
Schmickler Hans,
NiuSchwarz Jier,
Schwarz W. H. Eugen
Publication year - 2001
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 - 10.1002/1522-2675(20010613)84:6<1737::aid-hlca1737>3.0.co;2-h
Subject(s) - biphenylene , chemistry , dication , ring (chemistry) , thiophene , chemical shift , crystallography , delocalized electron , double bond , stereochemistry , computational chemistry , molecule , organic chemistry , phenylene , polymer
The bonding situation in a series of biphenylene analogues – benzo[ b ]biphenylene and its dication, 4,10‐dibromobenzo[ b ]biphenylene, naphtho[2,3‐ b ]biphenylene and its dianion, benzo[ a ]biphenylene, (biphenylene)tricarbonylchromium, benzo[3,4]cyclobuta[1,2‐ c ]thiophene, benzo[3,4]cyclobuta[1,2‐ c ]thiophene 2‐oxide, benzo[3,4]cyclobuta[1,2‐ c ]thiophene 2,2‐dioxide, 4,10‐diazabenzo[ b ]biphenylene, biphenylene‐2,3‐dione, benzo[3,4]cyclobuta[1,2‐ b ]anthracene‐6,11‐dione, and 3,4‐dihydro‐2 H ‐benzo[3,4]cyclobuta[1,2]cycloheptene – where one of the two benzo rings of biphenylene is replaced by a different π ‐system (B) was investigated on the basis of the NMR parameters of these systems. From the vicinal 1 H, 1 H spin‐spin coupling constants, the electronic structure of the remaining benzo ring (A) is derived via the Q ‐value method. It is found that increasing tendency of B to tolerate exocyclic double bonds at the central four‐membered ring of these systems favors increased π ‐electron delocalization in the A ring. The analysis of the chemical shifts supports this conclusion. NICS (nucleus‐independent chemical shift) values as well as C,C bond lengths derived from ab initio calculations are in excellent agreement with the experimental data. The charged systems benzo[ b ]biphenylene dication and naphtho[2,3‐ b ]biphenylene dianion ( 7 2− ) are also studied by 13 C NMR measurements. The charge distribution found closely resembles the predictions of the simple HMO model and reveals that 7 2− can be regarded as a benzo[3,4]cyclobuta[1,2‐ b ]‐substituted anthracene dianion. It is shown that the orientation of the tricarbonylchromium group in complexes of benzenoid aromatics can be derived from the vicinal 1 H, 1 H coupling constants.