THE STRUCTURE AND MECHANISM OF FORMATION OF C5H9O-ETHER( FROM IONIZEDPHYTYL METHYL)

The recent proposal that ionized phytyl methyl ether [C16H33(CH3)C = C HCH2OCH3+.] undergoes an allylic rearrangement to ionized isophytyl me thyl ether [CH2 = CHC(C16H33)(CH3)OCH3+.] before elimination of an alk yl radical is discussed. Both literature precedent and new results in which the structure of the [M - C16H33.](+) fragment ion is establishe d by comparison of its collision-induced dissociation mass spectrum wi th the spectra of isomeric C5H9O+ ions of known structure are inconsis tent with this proposal. The formation of CH3CH=CHCH=O+CH3 by loss of a gamma-alkyl substituent without Skeletal isomerization rather than C H2=CHC(CH3)=O+CH3 after allylic rearrangement is ex plained in terms o f a mechanism that involves two 1,2-H shifts, followed by sigma-cleava ge of the resultant ionized enol ether, C16H33(CH3)CH-CH = CHOCH3+..