Enhancement of Through-Space and Through-Bond p-Orbital Interactions. Syntheses and Properties of Permethylated and Perspirocyclopropanated Cyclotetradeca-1,3,6,9,12-pentayne.
The permethyhlated and perspirocyclopropanated cyclotetradeca-1,3,6,9,12-pentaynes (I) and (II) have been synthesized and completely characterized by 1H NMR, 13C NMR, UV, IR, and mass spectroscopy as well as by X-ray crystal structure anal. In the permethylated pentayne, compression of the internal C-C-C bond angles at the satd. carbon atoms flanking the diyne (103.8 Deg) enhances the through-space p-orbital interactions and causes a bathochromic shift in the long wavelength UV absorption max. (lmax 266 nm) relative to that of ref. compds. (lmax 255-259 nm). In the perspirocyclopropanated pentayne, wider internal C-C-C bond angles at the corresponding carbon atoms (109.2 Deg) reduce the through-space p-orbital interactions, but the through-bond p-orbital interactions are enhanced by spirocyclopropanation and cause a shift in the long wavelength UV absorption max. to even longer wavelength (lmax 273 nm).
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