The tert-butyl ion heat of formation and the isobutene proton affinity

Keister, Jeffrey W.; Riley, John S.; Baer, Tomas

doi:10.1021/ja00079a062

Cited by 45 publications

(38 citation statements)

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“…1͑b͒, resulting in the appearance energy of 74 011Ϯ38 cm Ϫ1 (9.1762Ϯ0.0047 eV) for the C 4 H 9 ϩ fragment. This value is in good agreement with the appearance energy of 9.180Ϯ0.015 eV measured with PEPICO spectroscopy by Baer and co-workers, 19 Table I. Using the heats of formation data for t-C 4 H 9 I and I products in the literature, 20,21 ⌬ f H 0 (t-C 4 H 9 ϩ ) is estimated to be 733.7Ϯ3.3 kJ mol Ϫ1 , which is in agreement with 734 Ϯ3.6 kJ mol Ϫ1 reported previously.…”

Section: A T-butyl Iodidesupporting

confidence: 92%

“…Using the heats of formation data for t-C 4 H 9 I and I products in the literature, 20,21 ⌬ f H 0 (t-C 4 H 9 ϩ ) is estimated to be 733.7Ϯ3.3 kJ mol Ϫ1 , which is in agreement with 734 Ϯ3.6 kJ mol Ϫ1 reported previously. 19 The experimental finding that relatively sharp peaks appear in the C 4 H 9 ϩ fragment MATI spectrum even above the fragmentation threshold suggests that both intramolecular vibrational redistribution ͑IVR͒ and fragmentation processes are not extremely fast near the fragmentation threshold, namely at ϳ1400 cm Ϫ1 above the zero point level. However, at higher excitation energies the fragment MATI spectrum shows broad and structureless feature, indicating that IVR becomes quite efficient at such energies.…”

Section: A T-butyl Iodidementioning

confidence: 99%

“…It is reasonable to assume that the C 4 H 9 ϩ fragment has the tertiary butyl structure also because it is the most stable among the C 4 H 9 ϩ isomers. 18,19 Fragmentation threshold energy can be estimated from the energy where the parent (C 4 H 9 I ϩ• ) MATI signal disappears and at the same time the C 4 H 9 ϩ fragment MATI signal starts to increase. However, as shown in Fig.…”

Section: A T-butyl Iodidementioning

confidence: 99%

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Vacuum-ultraviolet mass-analyzed threshold ionization spectra of iodobutane isomers: Conformer-specific ionization and ion-core dissociation followed by ionization

Park

Kim

2001

The Journal of Chemical Physics

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One-color two-photon mass-analyzed threshold ionization spectroscopy of ethyl bromide through a dissociative intermediate state Vacuum ultraviolet mass-analyzed threshold ionization spectroscopy of p -, m -, and o -difluorobenzenes. Ionization energies and vibrational frequencies and structures of the cations Dissociation dynamics of gauche and anti conformations of 1-iodopropane ions prepared selectively by vacuum-ultraviolet mass-analyzed threshold ionization spectrometry: Photodissociation at 426 and 355 nm

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Section: A T-butyl Iodidesupporting

confidence: 92%

Section: A T-butyl Iodidementioning

confidence: 99%

Section: A T-butyl Iodidementioning

confidence: 99%

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Vacuum-ultraviolet mass-analyzed threshold ionization spectra of iodobutane isomers: Conformer-specific ionization and ion-core dissociation followed by ionization

Park

Kim

2001

The Journal of Chemical Physics

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“…Furthermore, our calculated value for the proton affinity of alkene 5 is similar to the experimental value reported for isobutene. (42) The heats of reaction for the individual proton and hydrogen atom transfers are illustrated in Scheme 2. The data indicate that addition of a proton to either member of the alkyne/allene pair is approximately 15 kcal/mol less exothermic (δ) than protonation of the isomeric alkenes, reflecting the substantial difference in the stabilities of the vinyl and tertiary carbocations produced in the reactions.…”

Section: Resultsmentioning

confidence: 99%

Type II Isopentenyl Diphosphate Isomerase: Probing the Mechanism with Alkyne/Allene Diphosphate Substrate Analogues

2010

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Isopentenyl diphosphate isomerase (IDI) catalyzes the interconversion of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), the basic five-carbon building blocks of isoprenoid molecules. Two structurally unrelated classes of IDI are known. Type I IPP isomerase (IDI-1) utilizes a divalent metal in a protonation-deprotonation reaction. In contrast, the type II enzyme (IDI-2) requires reduced flavin, raising the possibility that the reaction catalyzed by IDI-2 involves the net addition/abstraction of a hydrogen atom. As part of our studies of the mechanism of isomerization for IDI-2, we synthesized allene and alkyne substrate analogues for the enzyme. These molecules are predicted to be substantially less reactive toward proton addition than IPP and DMAPP, but have similar reactivities toward hydrogen atom addition. This prediction was verified by calculations of gas phase heats of reaction for addition of a proton and of a hydrogen atom to 1-butyne (3) and 1,2-butadiene (4) to form the 1-buten-2-yl carbocation and radical, respectively, and related affinities for 2-methyl-1-butene (5) and 2-methyl-2-butene (6) using G3MP2B3 and CBS-QB3 protocols. Alkyne 1-OPP and allene 2-OPP were not substrates for Thermus thermophilus IDI-2 or Escherichia coli IDI-1, but instead were competitive inhibitors. The experimental and computational results are consistent with a protonation-deprotonation mechanism for the enzyme-catalyzed isomerization of IPP and DMAPP.

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“…[13], except for the following: AH~(m-CF3-C6H~-) = 56 kcal mol -l was estimated from the MNDO-calculated PA of PhCF 3 [14]; AH~f(Me3 C+) : 170 kcal mol -l was taken from Ref. [15]; A/~f(Me2F +) = 152 kcal tool -1 and AH~(Me2C1 +) = 184 kcal mol -l were derived from methyl cation affinities (MCA) of MeF and MeC1 [16(a)], corrected by the approximately 4 kcal mo1-1 difference of the recently revised value of MCA of Nz, the reference compound of the MCA scale [16 (b)]. AH~(p-Me3CC6H4Me ) = -13 kcal mol -l was estimated by group additivity rules.…”

Section: Radiolytic Reactionsmentioning

confidence: 99%

[Arene·Me3C+] non-covalent complexes in the gas-phase (trifluoro)methylation of tert-butyl-substituted diphenylalkanes

Chiavarino¹,

Crestoni²,

Fornarini³

et al. 1995

International Journal of Mass Spectrometry and Ion Processes

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The reaction of Me2 F+, MezC1 + and CF~-withp-Me3CC6H4(CH2)nC6D5 (n = 2, 3) initiates a reaction pattern whose major features are accounted for by the additional electrostatic stabilization afforded by the second (spectator) aromatic ring on ionic intermediates and ion-molecule complexes. The Me3C loss following CX~-(X = H, F) addition to the tertbutyl-substituted ring is significantly reduced with respect to a single-ring model substrate, p-Me3CC6H4Me. [Arene.Me3C +] non-covalent complexes mediate the observed interannular and intermolecular Me3 C+ transfer. Unimolecular cleavage of Me3CH from [arene.Me3C+], following side-chain H-abstraction, a major fragmentation pathway under mass spectrometric conditions, is instead largely inhibited in the reported radiolytic experiments. Such behavior is accounted for by the effective stabilization of ion-molecule non-covalent complexes ensured by unreactive collisions with about 1 arm bath gas.

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The tert-butyl ion heat of formation and the isobutene proton affinity

Cited by 45 publications

References 1 publication

Vacuum-ultraviolet mass-analyzed threshold ionization spectra of iodobutane isomers: Conformer-specific ionization and ion-core dissociation followed by ionization

Vacuum-ultraviolet mass-analyzed threshold ionization spectra of iodobutane isomers: Conformer-specific ionization and ion-core dissociation followed by ionization

Type II Isopentenyl Diphosphate Isomerase: Probing the Mechanism with Alkyne/Allene Diphosphate Substrate Analogues

[Arene·Me3C+] non-covalent complexes in the gas-phase (trifluoro)methylation of tert-butyl-substituted diphenylalkanes

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