- Transmission of Polar Substituent Effects through the Bicyclooctane Ring System as Monitored by 19F NMR Shifts: A 19F NMR Study of 10-Substituted 9-Fluorotriptycenes and 4-Substituted 4'-Fluorobibicyclooctanes
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A series of 10-substituted 9-fluorotriptycenes (5) encompassing a wide range of substituents has been synthesized and characterized, and the 19F chemicql shifts have been measured in several solvents.Multiple linear regression analysis reveals no discernible relationship between the 19F substituent chemical shifts (SCS) of 5 and polar substituent constants.Comparisons have been made between 5 and corresponding 4-substituted bicyclooct-1-yl fluorides (1), which strongly corroborate the previous interpretation of the 19F SCS of the latter system.In particular, the "through-bond" nature of the strong electronegativity effect (?x) in 1 seems established.A more restricted series of 4-substituted 4'-fluorobibicyclooctanes (6) have been acquired, and the pattern of shifts has been found to parallel polar field constants (?F values).In contrast to 1, no evidence for a significant ?x effect is apparent in 6.The pronounced sensitivity of 6 to electric field effects prompted its use in the determination of an unequivocal ?F value for the CH3 group.
- Adcock, William,Iyer, V. Sankar
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p. 5259 - 5266
(2007/10/02)
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