REACTIONS OF IONIZED DIBUTYL ETHER

The reactions of ionized di-n-butyl ether are reported and compared with those of ionized n-butyl sec-butyl and di-sec-butyl ether. The main fragmentation of metastable (CH3CH2CH2CH2)(2)O-+. is C2H5. loss (similar to 85%), but minor amounts (2-4%) of CH3., C4H7., C4H9., C4H10 and C4H10O are also eliminated. In contrast, C2H5. elimination is of much lower abundance (20 and 4%, respectively) from metastable CH3CH2CH2CH2OCH(CH3)CH2CH3+. and [CH3CH2(CH3)CH]O-2(+.) which expel mainly C2H6 and CH3. (35-55%). Studies on collisional activation spectra of the C6H13O+ oxonium ions reveal that C2H5. loss from (CH3CH2CH2CH2)(2)O-+. gives the same product, (CH3CH2CH2CH2+O=CHCH3) as that formed by direct cleavage of CH3CH2CH2CH2OCH(CH3)CH2CH3+.. Elimination of C2H5. from (CH3CH2CH2CH2)(2)O-+. is interpreted by means of a mechanism in which a 1,4-H shift to the oxygen atom initiates a unidirectional skeletal rearrangement to CH3CH2CH2CH(2)OCH(CH3)CH2CH3+., which then undergoes cleavage to CH3CH2CH2CH2 O-+=CHCH3 and C2H5.. Further support for this mechanism is obtained from considering the collisional activation and neutralization-reionization mass spectra of the (C4H9)(2)O-+. species and the behaviour of labelled analogues of (CH3CH2CH2CH2)(2)O-+.. The rate of ethyl radical loss is suppressed relative to those of alternative dissociations by deuteriation at the gamma-position of either or both butyl substituents. Moreover, C2H5. loss via skeletal rearrangement and fragmentation of the unlabelled butyl group in CH3CH2CH2CH2OCH2CH2CD2CH3+. occurs approximately five times more rapidly than C2H4D. expulsion via isomerization and fission of the labelled butyl substituent. These findings indicate that the initial 1,4-hydrogen shift is influenced by a significant isotope effect, as would be expected if this step is rate limiting in ethyl radical loss.