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  • Open Daily: 10am - 10pm
    Alley-side Pickup: 10am - 7pm

    3038 Hennepin Ave Minneapolis, MN
    612-822-4611

Open Daily: 10am - 10pm | Alley-side Pickup: 10am - 7pm
3038 Hennepin Ave Minneapolis, MN
612-822-4611
The Structure of Bromonium, Chloronium, and Oxonium Ions.

The Structure of Bromonium, Chloronium, and Oxonium Ions.

Schubert, Jeffrey W.

Paperback

Chemistry

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ISBN10: 1243014814
ISBN13: 9781243014818
Publisher: Proquest Umi Dissertation Pub
Pages: 76
Weight: 0.37
Height: 0.20 Width: 7.99 Depth: 10.00
Language: English
Isotopic perturbation of equilibrium is used to study the structure of cyclic bromonium and chloronium ions under superacidic conditions. The 13C NMR spectrum of the five-membered ring generated from ionization of 1,4-dichlorobutane-d2 exhibits intrinsic isotope shifts only, and is consistent with a symmetric structure. The 13C NMR spectra of ions generated from 2,3-dibromo-2,3-dimethylbutane- d3, 2,3-dibromo-2,3-dimethylbutane-d 6, and 2,3-dichloro-2,3-dimethylbutane-d3 (dichloropinacolone?) exhibit small intrinsic isotope shifts and large equilibrium isotope shifts. These species do not exist as symmetric 1,2-bridged structures, but as a rapidly equilibrating mixture of beta-halocarbenium ions. Computational investigations suggest formation of a complex containing a solvent molecule and a halonium ion. The mechanisms associated with isomerization of the O-methylethylene oxonium ion and its mono-, di-, tri-, and tetramethyl substituted analogs are also explored. Evaluation of methods and basis sets indicate that the B3LYP/6-31G* level of theory is reliable for geometry optimizations; the higher order MP2/cc-pVTZ level of theory is needed to obtain accurate relative energies. The transition states leading to O-methyl inversion and epoxide opening are characterized. The inversion barrier relative to the symmetric 1,2-bridged oxonium ion is ∼15 kcal/mol for all species; the barrier to ring-opening is 35.3 kcal/mol for O-methylethylene oxonium and decreases with greater substitution of the epoxide carbon involved in cleavage.

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