Mechanism of keto Å enol tautomerism of ionized vinyl alcohol versus acetaldehyde and their dissociation to C2H3O+ and H·. An ab initio molecular orbital study

Apeloig, Yitzhak; Karni, Miriam; Ciommer, Bernhard; Depke, Gisbert; Frenking, Gernot; Meyn, Stefan; Schmidt, Johann Friedrich Julius; Schwarz, Helmut

doi:10.1016/0168-1176(84)87067-6

Cited by 61 publications

(13 citation statements)

References 52 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…It is well established that ionized glycine in its enol form is thermodynamically more stable than in its keto form, in agreement with many other pairs of keto/enol tautomers of radical cations 19,. 20 For this reason we have chosen the enol cation radical as starting species in our PESs. The potential energy surfaces for [H 2 NCHC(OH) 2 ] +· fragmentation into H 2 O and [H 2 N–HCCO] +· , obtained at B3LYP and MP2 levels, are reported in Fig.…”

Section: Resultsmentioning

confidence: 76%

On the fragmentation pathway of the ionized enol of glycine in the gas phase

Marino

Russo

2001

Rapid Comm Mass Spectrometry

View full text Add to dashboard Cite

Density functional and second-order many body perturbation approaches were used to compute the potential energy surface for the fragmentation of the ionized enol of glycine [H2NCH = C(OH)2]+* into water and aminoketene radical cation [H2N-HC = CO]+*. Two possible pathways were considered. The potential energy surfaces obtained are very similar and both predict the existence of a molecular complex in which the water is coordinated to the aminoketene moiety in two different fashions with a noticeable binding energy. The fragmentation is kinetically controlled by the step in which the molecular complex is formed from the most stable cation enol of glycine. Our quantum-mechanical data confirm the hypothesis that the ylide ion [H3NCHCOOH]+* is an intermediate in the water loss.

show abstract

Section: Resultsmentioning

confidence: 76%

On the fragmentation pathway of the ionized enol of glycine in the gas phase

Marino

Russo

2001

Rapid Comm Mass Spectrometry

View full text Add to dashboard Cite

show abstract

“…We have not succeeded in locating TS2 in our ab initio calculations, but note that the activation energy associated with a similar ''rotational'' isomerization in H 2 O-HOH 2 ϩ is 0.534 eV, 17 and that an analogous rotational isomerization is found in the C 6 H 5 O-HND 3 ϩ system, with an activation energy of ϳ0.25 eV. Once in the C2 geometry, the system can dissociate directly to CH 3 CDO ϩ ϩHDO.…”

Section: Ab Initio Resultsmentioning

confidence: 87%

“…[1][2][3][4][5] It is possible, however, that in collisions, the barriers to isomerization might be substantially lowered. The reactant keto form (CH 3 CHO ϩ ) is Ϫ0.62 eV less stable than the enol form (CH 2 CHOH ϩ ), and isomerization can occur by either direct C-to-O proton transfer, or by sequential 1,2 proton shifts (CH 3 CHO ϩ →CH 3 COH ϩ →CH 2 CHOH ϩ ).…”

Section: Introductionmentioning

confidence: 99%

Reaction of acetaldehyde cations with water: The effects of CH3CHO+ vibrational mode and impact parameter on reactivity and product branching

Kim

Anderson

2001

The Journal of Chemical Physics

View full text Add to dashboard Cite

Articles you may be interested inVibrational mode and collision energy effects on reaction of H 2 CO + with C 2 H 2 : Charge state competition and the role of Franck-Condon factors in endoergic charge transfer Scattering of mode-selectively excited acetaldehyde cations from D 2 O was studied in a guided ion beam instrument. The effects of reactant vibrational state and collision energy on reactivity, product branching, and product ion recoil velocity distributions were measured. Ab initio calculations were performed to help understand the reaction coordinate. The dominant reaction is H/D exchange, which occurs in about 40% of low energy collisions, dropping to just a few percent at high energies. H/D exchange is also inhibited by CH 3 CHO ϩ vibration, but with a smaller effect than the equivalent amount of collision energy. H/D exchange is mediated by a long-lived complex, and several candidates are identified. The other low energy channel corresponds to methyl elimination from the collision complex. This channel is the most energetically favorable, but is only a few percent efficient, even at low energies, and is negligible at high energies. Methyl elimination is strongly suppressed by both collision energy and vibration, and the vibrational effects are nonmode specific. The most interesting channel is proton transfer ͑PT͒, which occurs by a direct mechanism at all collision energies. At low energies, PT occurs only in small impact parameter collisions, while at high energies, PT occurs primarily for large impact parameters, and is suppressed for small impact parameters. PT also shows strongly mode-specific dependence on CH 3 CHO ϩ vibrational state.

show abstract

“…For many years, it has been known that the keto-enol isomerization of an ionized aldehyde or ketone in the gas phase involves a large energy barrier [1][2][3][4][5]. These barriers generally lie at energy above the lowest dissociation threshold for the carbonyl compound and so the isomerization is never directly observed for the isolated ion.…”

Section: Introductionmentioning

confidence: 99%