Jiao H, van Eikema Hommes NJR, von Ragué Schleyer P. Can bridged 1,6-X-[10]annulenes (X = SiH(2), SiMe(2), PH, and S) exist?
Org Lett 2002;
4:2393-6. [PMID:
12098255 DOI:
10.1021/ol026144v]
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Abstract
[structure: see text] In contrast to the 1,6-X-[10]annulenes (X = CH(2), O, NH) with delocalized forms (c), their X = PH and S counterparts favor the bisnorcaradiene structures (b). Forms b and c are close in energy with X = SiH(2) and SiMe(2). The computed nucleus independent chemical shifts (NICS), show both annulenes (c) and cyclic polyenes (a) to be aromatic. Strain-introduced structural localization, e.g., due to four bulky SiMe(3) substituents, reduces but does not eliminate aromaticity.
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