THE MECHANISM OF ALKYL RADICAL ELIMINATION FROM IONIZED GAMMA,GAMMA-DISUBSTITUTED ALKENYL METHYL ETHERS

The mechanism of alkyl radical loss from ionised alkenyl methyl ethers containing two gamma-alkyl substituents, R(1)R(2)C=CHCH2OCH3+., has b een studied by investigating the collision-induced dissociation spectr a of the resultant CnH2n-1O+ oxonium ions (n = 5-7), Comparison of the se spectra with one another and those of reference ions generated by d issociative ionisation of secondary allylic alkenyl methyl ethers indi cates that expulsion of a gamma-alkyl group occurs without isomerisati on of the heavy atom skeleton via an allylic rearrangement, This findi ng is consistent with the occurrence of two consecutive 1,2-H shifts i n R(1)R(2)C=CHCH2OCH3+., followed by gamma-cleavage of the ionised eno l ether, R(1)R(2)CHCH=CHOCH3+., to give R(1)CH=CHCH=OCH3+ or R(2)CH=CH CH=OCH3+. Thus, CH3CH2CH2(CH3CH2)C=CHCH2OCH3+. loses C2H5. and C3H7. t o yield CH3CH2CH2CH=CHCH=OCH3+ and CH3CH2CH=CBCH=OCH3+, respectively.