Dependence of H-1 and C-13 NMR chemical shifts on the PAH : FSO3H ratios for 4H-cyclopenta[def]phenanthrenium and pyrenium cations in SO(2)C1F. Possible existence of cation-anion interactions and coexistence of PAHH(+)-PAH

For two representative delocalized PAH-carbocations, namely the C-l protona ted 4H-cyclopenta[def]phenanthrenium cation 1H(+) and the C-l protonated py renium cation 2H(+), generated in FSO3H-SO2CIF, the FSO3H:PAH molar ratio a nd the absolute concentration of the arenium ions were systematically varie d over a wide range (FSO3H:PAH molar ratios were varied from 71 to 1 for 1H (+) and from 69 to 5 for 2H(+) in 0.3 mt of SO2CIF and 0.05 mt of CD2Cl2 at - 75 degrees C). In selected cases, the H/H COSY and C/H HETCOR spectra we re used to fully assign the resonances. Shielding of the PAH-arenium ion pr otons and carbons was observed with decreasing FSO3H:PAI ratios without not iceable line-broadening. This is attributed tb cation-anion interactions in the low FSO3H:PAH domain and possible formation of contact ion pairs. Lowe ring the ratio (below 35 in the case of 1 and below 10 for 2) gave separate sets of resonances for the unprotonated PAH, indicative of the presence of the equilibrium: PAH + FSO3H reversible arrow PAHH(+) + FSO3-. The observe d shielding of the unprotonated PAH in the equilibrium as compared to the s tarting material in CDCl3, is attributed to solvation by FSO3H, although po ssible formation of PAHH(+) FSO3--PAH ion pair-molecule clusters is not rul ed out.