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An extensive series of mixtures of exoand endo-6-substituted(X)-exo-2-fluorobicyclo[2.2.1] heptanes (4 and 5, respectively) were synthesized and characterized by C NMR and their F chemical shifts measured. Additionally, the latter parameters for a more limited series of 4and 4-substituted (X) 2-fluoroadamantanes (9 and 10, respectively) were also obtained. The corollary from correlations of the F substituent chemical shifts(SCS) of 4 and 5 versus the corresponding results for the known 4-substituted(X)bicyclo[2.2.1]hept-1-yl fluorides(3) is that electronegativity effects (σχ effect) underly the SCS of 4 and 5. Differences between the SCS of 4 and 5 as well as 9 and 10 indicate that there is a stereoelectronic component to the polar effect significantly determining the F SCS of 4 and 9. F NMR shieldings of 3, 4, 5, 3-substituted(X) adamant-1-yl fluorides (8), 9 and 10 for a common set of substituents (X = H, NO2, CN, NC, CF3, COOH, F, Cl, HO, NH2, CH3, Si(CH3)3 and Li) were calculated using the DFT-GIAO theoretical model. The level of theory, B3LYP/6-31+G*, was chosen based on trial calculations which gave good agreement with experimental values where known. By means of NBO analysis various molecular parameters were obtained from the optimized geometries. Linear regression analysis was employed to explore the relationship between the calculated F SCS and polar field and group electronegativity substituent constants(σF and σχ, respectively) and also the NBO derived molecular parameters( fluorine natural charges(Qn), electron occupancies on fluorine of lone pairs(nF), and occupation number of the C-F antibonding orbital(σCF*)). The key determining parameters appear to be nF and σCF*(occup).

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Nature of transmission of polar substituent effects in γ-disposed bicyclo[2.2.1]heptane (norbornane) and adamantane ring systems as monitored by 19F NMR: A DFT- GIAO and – NBO analysis