Hydroacridines: part 29. ¹⁵N NMR chemical shifts of 9‐substituted 1,2,3,4,5,6,7,8‐octahydroacridines and their N‐oxides—Taft, Swain–Lupton, and other types of linear correlations

The ¹⁵N NMR chemical shifts of 1,2,3,4,5,6,7,8‐octahydroacridine, 12 of its 9‐substituted derivatives, and of the corresponding N‐oxides were measured and examined in terms of the 9‐substituent effects and the effects of N‐oxidation. For the 9‐substituent effects, good linear correlations were found with the Taft and Swain‐Lupton substituent constants, for both octahydroacridines and their N‐oxides. The ¹⁵N chemical shifts of both octahydroacridines and their N‐oxides also correlate well, linearly with the ¹³C chemical shifts of the para‐carbons in analogously substituted benzene derivatives.Within the studied compounds, the magnitudes of the N‐oxidation effects range from − 16.4 to − 27.4 ppm (shielding), and also correlate linearly with the Taft and Swain–Lupton substituent constants, as well as with the bond orders of the N⁺O⁻ bonds in the corresponding N‐oxides. Furthermore, a very good linear correlation is found between the ¹⁵N chemical shifts of octahydroacridines and those of the corresponding N‐oxides. From the ¹⁵N chemical shifts data, the Taft and Swain‐Lupton substituent constants for the diacetylamino group (NAc₂) were evaluated in the present paper, as follows: σ_R = 0.07 and σ_I = 0.15; ${{\cal R}} = 0.08$ and ${{\cal F}} = 0.20$ . Copyright © 2008 John Wiley & Sons, Ltd.