. Can. J. Chem. 60, 3077 (1982). The addition of crown ethers 1,4,7,10,13-pentaoxacyclopentadecane ( 1 5 0 ) and 1,4,7,10,13,16-hexaoxacyclooctadecane (18C6) in quantities equimolar to the base, to p-elimination reactions of l,l,l-trifluoro-2,2-di(4-nitropheny1)ethane and 1-fluoro-2,2-di(4-nitropheny1)ethane promoted by sodium methoxide in methanol, has been investigated. In the E2 reaction of the monofluoro compound, the crown ethers caused no change in the kinetic order and only small changes in the second-order rate constants and activation parameters. The primary deuterium isotope effect was also unaltered by the presence of crown ethers.For the (ElcB), reaction of the trifluoro compound, no change in kinetic order was found, but slightly larger rate constant changes and an increase in the isotope effect from k,lkD = 1.0 to 1.25 at 25°C was observed. This is interpreted a s an alteration in mechanism from (ElcB), towards (ElcB),.