A STUDY of the 13C NMR SHIFTS in TWO TETRADEHYDROCYCLODECABIPHENYLENES and RELATED ARYL and BIPHENYLENYLACETYLENES.

Article abstract of DOI:10.1016/S0040-4020(01)82336-X

The 13C spectra of 5,6,9,10-tetradehydrocyclodeca<1,2,3,4-def>-benzo<7,8>biphenylene, 1, and 5,6,9,10-tetradehydrocyclodeca<1,2,3,4-def>-naphtho<2,3-7,8>biphenylene, 2, are reported as are those of a number of simpler acetylenic hydrocarbons used as spectral references.Most of the shifts can be assigned unambiguously.The acetylenic shift assignments were verified by ortho-proton, sp-carbon <1H(1)-13C_sp(3)> decoupling experiments.A simple additive shift correlation is found for the hydrocarbons containing unstrained acetylenic groups.However, significant discrepencies are found for the 13C shifts for the strained hydrocarbons 1, 2, 1,2-bis(phenylethynyl)-benzene, 12, and 2,3-bis(phenylethynyl)naphthalene, 13.The discrepencies are particularily large for carbons near the triple bonds and are attributed to a combination of strain, rehybridization, and other proximity effects related to the interaction between the ortho-substituted acetylenic carbons.