Comparative studies of the reduction of 2-naphthaldehyde, 9,9′-spirobi-(9H-fluorene)-2-carboxaldehyde and 2-fluorenecarboxaldehyde in nonaqueous solvents

The reductions of 2-naphthaldehyde, (3), 9,9′-spirobi-(9H-fluorene)-2-carboxaldehyde, (2), and 2-fluorenecarboxaldehyde, (4), have been studied in N,N-dimethylformamide (DMF) and acetonitrile. Putative spiroconjugation was the source of interest in 2 and its formal potential for the neutral/radical anion couple and the rate constant for dimerization of the radical anions were compared with the same quantities for 3 and 4. In DMF the range of formal potentials for 2-4 is only 100 mV and the rate constants for the three aldehydes differ by a factor of two. These small differences are consistent with insignificant spiroconjugative effects. The effect of added water on the dimerization rate constant for the radical anions of 3 has been interpreted in terms of reversible dimerization to a dimer dianion followed by irreversible protonation of the dianion by water.