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Title: Extreme Projection of a Proton into the π-Cloud of an Aromatic Ring: Record Shielding of an Aromatic Proton in trans-10b-Methyl-10c-(1-naphthyl)-10b,10c-dihydropyrene
Authors: Ting, Y.
Lai, Y.-H. 
Issue Date: 28-Jan-2004
Citation: Ting, Y., Lai, Y.-H. (2004-01-28). Extreme Projection of a Proton into the π-Cloud of an Aromatic Ring: Record Shielding of an Aromatic Proton in trans-10b-Methyl-10c-(1-naphthyl)-10b,10c-dihydropyrene. Journal of the American Chemical Society 126 (3) : 909-914. ScholarBank@NUS Repository.
Abstract: A synthetic sequence involving dithiametacyclophane → metacyclophanediene → dihydropyrene was employed to prepare trans-10b-methyl-10c-(2-naphthyl)- and trans-10b-methyl-10c-(1-naphthyl)-10b, 10c-dihydropyrene 5 and 6, respectively. Both exhibit a strong diamagnetic ring current despite the introduction of an internal bulky substituent within the π-electron cloud. Their electronic spectra suggest interaction between the two near-perpendicular naphthyl and dihydropyrenyl π systems, resulting in red shift and band broadening. All naphthyl protons are well resolved in their 1H NMR spectra due to a strong shielding effect of the dihydropyrene ring. The most shielded protons in 5 and 6 are H1′ and H2′ at δ 2.47 and 1.42, respectively, being 5.25 and 5.95 ppm shifted from those of reference protons. There is evidence for free rotation on the NMR time scale of the 2-naphthyl ring in 5 with a preference for a particular conformer, whereas the 1-naphthyl ring in 6 is conformationally rigid with its H2′ projecting deeply into the π-cloud, thus accounting for the most shielded aromatic proton (H2′ in 6) reported to date.
Source Title: Journal of the American Chemical Society
ISSN: 00027863
DOI: 10.1021/ja038380m
Appears in Collections:Staff Publications

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