Site-selective deuterium labeling of the tetrabutylammonium cation
摘要:
Four separate selectively deuterated samples of tetrabutylammonium iodide have been prepared in which each one of the four nonequivalent alkyl carbons is separately and fully deuterated. These samples were prepared for nuclear magnetic resonance (NMR) studies of the aggregation of ion pairs in low polarity solvents.
Site-selective deuterium labeling of the tetrabutylammonium cation
摘要:
Four separate selectively deuterated samples of tetrabutylammonium iodide have been prepared in which each one of the four nonequivalent alkyl carbons is separately and fully deuterated. These samples were prepared for nuclear magnetic resonance (NMR) studies of the aggregation of ion pairs in low polarity solvents.
AbstractThe 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)2O+. is C2H5⋅ loss (˜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]2O+., which expel mainly C2H6 and CH3⋅ (35–55%). Studies on collisional activation spectra of the C6H13O+ oxonium ions reveal that C2H5⋅ loss from (CH3CH2CH2CH2)2O+. gives the same product, (CH3CH2CH2CH2+OCHCH3) as that formed by direct cleavage of CH3CH2CH2CH2OCH(CH3)CH2CH3+.. Elimination of C2H5⋅ from (CH3CH2CH2CH2)2O+. is interpreted by means of a mechanism in which a 1,4‐H shift to the oxygen atom initiates a unidirectional skeletal rearrangement to CH3CH2CH2CH2OCH(CH3)CH2CH3+., which then undergoes cleavage to CH3CH2CH2CH2+OCHCH3 and C2H5⋅. Further support for this mechanism is obtained from considering the collisional activation and neutralization‐reionization mass spectra of the (C4H9)2O+. species and the behaviour of labelled analogues of (CH3CH2CH2CH2)2O+.. The rate of ethyl radical loss is suppressed relative to those of alternative dissociations by deuteriation at the γ‐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.
Site-selective deuterium labeling of the tetrabutylammonium cation
Four separate selectively deuterated samples of tetrabutylammonium iodide have been prepared in which each one of the four nonequivalent alkyl carbons is separately and fully deuterated. These samples were prepared for nuclear magnetic resonance (NMR) studies of the aggregation of ion pairs in low polarity solvents.