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HERO ID
1193660
Reference Type
Journal Article
Title
GAS-PHASE DECOMPOSITION OF CONJUGATE ACID IONS OF SIMPLE TERT-BUTYL ALKYL ETHERS
Author(s)
Audier, HE; Berthomieu, D; Morton, TH
Year
1995
Is Peer Reviewed?
Yes
Journal
Journal of Organic Chemistry
ISSN:
0022-3263
EISSN:
1520-6904
Volume
60
Issue
22
Page Numbers
7198-7208
Language
English
DOI
10.1021/jo00127a027
Web of Science Id
WOS:A1995TD63700027
URL
https://www.scopus.com/inward/record.uri?eid=2-s2.0-0001500215&doi=10.1021%2fjo00127a027&partnerID=40&md5=64ae1054bd3d06ffef0ccaedd3eb5450
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Abstract
Unimolecular decompositions of protonated methyl (MTBE), ethyl (ETBE), n-propyl, isopropyl, and isobutyl tert-butyl ethers have been examined experimentally and the results compared with the outcome of ab initio calculations. Extensive hydrogen transposition between the hydrogen on oxygen and the nine hydrogens of the tert-butyl is revealed by mass-resolved ion kinetic energy spectroscopy (MIKES) experiments on deuterated ions from MTBE and ETBE. Mechanistic possibilities are probed with the help of FT-ICR, and isotope effects are interpreted by comparison with the MIKES of protonated ethyl tert-amyl ether and its deuterated analogues. Protonated MTBE displays a single unimolecular decomposition product, tert-butyl cation. Of the protonated MTBE ions that decompose, 30% do so without any hydrogen transposition, while 70% completely randomize the non-methoxy hydrogens. This calls for the intervention of at least two noncovalent intermediates. In the case of MTBE, Hartree-Fock-based SCF computations exhibit only one plausible candidate that corresponds to an energy minimum, the hydrogen-bonded complex between protonated methanol and isobutene. The other intermediate is inferred to be the ion-neutral complex [MeOH tBu(+)], even though that does not correspond to a well on the SCF potential energy surface. Protonated ETBE yields a pair of unimolecular decomposition products, tert-butyl cation and protonated acetaldehyde. Here the ab initio results display two noncovalent potential energy minima, but the observed ion intensities cannot be accounted for without at least three intermediates. Again, the conclusion is that the additional intermediate corresponds to an ion-neutral complex, [EtOH tBu(+)], which does not correspond to a potential energy minimum. The transient ion-neutral complexes have non-zero lifetimes because their collapse is prevented by entropic (rather than energetic) barriers.
Keywords
MOLECULE REACTIONS; NEUTRAL COMPLEXES; METHYL-ETHER; ALCOHOLS; SUBSTITUTION; SOLVOLYSIS; OXIDATION; KINETICS; PRODUCTS; ANALOGS
Tags
•
tert-Amyl ethyl ether (TAEE)
Initial Litsearch 6/2018
WOS
•
ETBE
Database Searches
Combined Dataset (After duplicates removed electronically)
Excluded / Not on Topic
Chemical analysis/fuel chemistry
•
Methanol (Non-Cancer)
Search 2012
WOS
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