Meta-Benzyne reacts as an electrophile

Journal of Physical Chemistry A

Volumn 105, Issue 44, 2001, Pages 10155-10168

  Nelson, Eric D ^a   Artau, Alexander ^a   Price, Jason M ^a   Tichy, Shane E ^a   Jing, Linhong ^a   Kenttämaa, Hilkka I ^a  

^a PURDUE UNIVERSITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ELECTROPHILES; NUCLEOPHILES;

CHEMICAL BONDS; DISSOCIATION; GROUND STATE; PHOTOELECTRON SPECTROSCOPY;

AROMATIC COMPOUNDS;

EID: 0035829947     PISSN: 10895639     EISSN: None     Source Type: Journal    
DOI: 10.1021/jp011254p     Document Type: Article

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52. Based on the collision rate predictions of the method of Reference 21.
53. This reaction was carried out in the central quadrupole rather than the flow tube to avoid confusion from an isomeric contaminant corresponding to an electrostatic cluster of the 4-tert-butylpyridinium trifluoroborate zwitterion and the N-(3,5-didehydrophenyl)-4-tert-butylpyridinium ion.
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56. 5 as (alternately) the nucleophile or leaving group. The efficiencies measured in both cases agree to within the experimental error.
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61. The reverse of this reaction, CAD of 3-chlorophenide to form chloride and meta-benzyne, was used to measure the heat of formation of meta-benzyne by Wenthold et al. (Reference 1) and appears to be in good agreement with high-level theoretical calculations (Cramer, et al. Chem. Phys. Lett. 1997, 277, 311-320 and references therein).
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76. Cramer, C. J.; Debbert, S. Chem. Phys. Lett. 1998, 287, 320-326.) that predict that didehydropyridinium ions possess singlet-triplet gaps only slightly perturbed from that of the analogous benzyne.
77. We have confirmed this for the species discussed in this paper by using the hyperfine coupling method of Cramer, et al. (J. Phys. Chem. A 1997, 101, 9191-9194.).
78. The double-well potential energy surface characteristic of ion-molecule reactions can often result in the transition state lying below the reactants in energy (e.g., Figure 2). In effect, the thermal energy of the system is augmented by electrostatic ion-molecule solvation energy that helps to overcome the chemical barrier. This can often result in faster reactions than are observed for neutral species. However, the relative reaction rates of ion-molecule reactions are affected by perturbations in the barrier height in a manner roughly analogous to neutral species (i.e., directly proportional to the ratio of the sums of states above each transition state). See for example: (a) Olmsteadm, W. N.; Brauman, J. I. J. Am. Chem. Soc. 1977, 99, 4219-4228.
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82. Homolytic dissociation is estimated to be ∼0 kcal/mol more exothermic than heterolytic dissociation based on IE and EA values from References 32 and 54. However, homolytic dissociation is presumably accompanied by a barrier, and it is unclear whether a direct or two-step process takes place.
83. Cramer, C. J.; Debbert, S. Chem. Phys. Lett. 1998, 287, 320-326.