Chemical and spectroscopic studies related to the Lewis acidity of lithiumperchlorate in diethyl ether

Polarimetric studies on camphor (2) as well as IR studies on crotonaldehyde (CA; 1) and benzonitrile (BN; 3) confirm the conclusion of a previously pu blished NMR study on crotanaldehyde that lithium perchlorate (LP) weakly bi nds to probe bases in diethyl ether (DE). The weak binding is a consequence of the fact that the lithium ion (actually the LP ion pair and higher aggr egates), a powerful Lewis acid in the gas phase, competitively binds to eth er and the added base. Methylene camphor (5), (E)-1,3-pentadiene (4), camph ene, and phenylacetylene (6) do not bind to LP in DE. Shifts to lower energ y of the C=O modes of CA in ether solutions containing increasing amounts o f LP are consistent with moderate increases in solvent polarity. Only small or no shifts are seen in the C=N modes of BN and its 1:1 complex with adde d LP. Because the C=N and especially C=O modes are blue shifted under exter nal applied pressure, the large internal pressures of LPI DE do not mimic e xternal applied pressure. Likewise, the small or no changes observed in lam bda(max) for the absorption and emission spectra of anthracene (9) and azul ene (8) in ether as a function of LP concentration do not conform to what i s observed under external applied pressure. Studies of the Diels-Alder reac tion of (E)-1,3-pentadiene with methyl acrylate show that the reaction is e ntirely catalyzed in LP/DE; polarity and internal pressure do not influence product selectivity in this reaction.