COLLISION-INDUCED ELIMINATION OF ALKENES FROM DEPROTONATED UNSATURATED ETHERS IN THE GAS-PHASE - REACTIONS INVOLVING SPECIFIC BETA-PROTON TRANSFER

Unsaturated ethers CH2=CHCH2(CH2)nOR deprotonate in the gas phase to form CH2=CHCH(CH2)nOR. WhenR ≥ Et it was anticipated that collisional activation should cause β-proton transfer to the carbanion site to form the ElcBintermediate CH2=CH(CH2)n+1OCH2CH2- (R = Et), which should then eliminate ethene to yield the alkoxide CH2=CH-(CH2)n+1O-. This is the predominant reaction when n = 1 and 2 but diminishes in importance as the value of n increases. When n = 0, the β-proton transfer occurs to the methine position on the double bond, yielding deprotonated acetone as the product anion. Evidence is presented that suggests the following mechanism: CH2=CHCHOEt -C2H4 CH2CH2CHO →CH2CH2CHO- → (MeCOCH2)-. © 1990, American Chemical Society. All rights reserved.