Studies of the variations in bond dissociation energies of aromatic compounds. I. Mono-bromo-aryles

1953 ◽  
Vol 219 (1138) ◽  
pp. 341-352 ◽  
Keyword(s):  
Hydrogen Bromide ◽  
Heat Of Formation ◽  
Activation Energies ◽  
Bond Dissociation Energies ◽  
First Order ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Rate Determining Step ◽  
First Order Kinetics ◽  
Aromatic Radicals

Investigation of the pyrolyses of bromobenzene, β -bromonaphthalene, α -bromonaphthalene, 9-bromophenanthrene and 9-bromoanthraeene in the presence of an excess of toluene has shown that reaction (1) Ar .Br → Ar • + Br (1) is the primary and rate-determining step of the pyrolysis. The progress of reaction was measured by the rate of formation of hydrogen bromide, and it was shown that this rate obeys first-order kinetics. The following values were obtained for the activation energies and frequency factors of unimolecular decompositions represented by equation (1): compound E (kcal/mole) 10 -13 v (sec -1 ) bromobenzene 70.9 2 β -bromonaphthalene 700 1.5 α -bromonaphthalene 70.9 3.5 9-bromophenanthrene 67.7 1 9-bromoanthracene 65.6 1.5 Assuming that recombination of bromine atoms with aromatic radicals does not involve any activation energy we conclude tha t the determined activation energies correspond to the respective C—Br bond dissociation energies. The effect of molecular structure on the C—Br bond dissociation energy is discussed. The heat of formation of the phenyl radical is determined, and this result is used for calculating the various Ph — X bond dissociation energies.

scholarly journals Allyl radicals from 3,3′-azo-1-propene

1970 ◽  
Vol 48 (17) ◽  
pp. 2745-2754 ◽  
Author(s):  
Basil H. Al-Sader ◽  
Robert J. Crawford
Keyword(s):  
Activation Energies ◽  
Major Product ◽  
Bond Dissociation Energies ◽  
Kcal Mole ◽  
Allyl Radical ◽  
First Order ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
First Order Kinetics

3,3′-Azo-1-propene (4), 3,3′-azo-1-propene-3,3′-d2 (5) and 3,3′-azo-1-propene-3,3,3′3′-d4 (6) have been synthesized and characterized. Thermolysis of 4, at 40–300 Torr, and in the region 150–170°, followed first order kinetics (Ea = 36.1 ± 0.2 kcal mole−1, log A = 15.54 ± 0.10) the major product, >99.9%, being 1,5-hexadiene (9). The presence of less than 0.1% propene suggests that the allyl radical is unable to abstract hydrogen from 4 or 9. Statistical scrambling of deuterium, in the products of thermolysis of 5 and 6, was observed. These results are interpreted in terms of a mechanism wherein allyl radicals are generated. Comparison of the activation energies for azoalkanes and 4 with the bond dissociation energies of hydrocarbons suggest that a good Polanyi plot is possible.

The pyrolysis of benzoyl bromide and the determination of the relevant bond dissociation energies

1952 ◽  
Vol 214 (1117) ◽  
pp. 273-280 ◽  
Keyword(s):  
Least Square Method ◽  
Heat Of Formation ◽  
Least Square ◽  
Bond Dissociation Energies ◽  
Kcal Mole ◽  
Bond Dissociation ◽  
Rapid Decomposition ◽  
Dissociation Energies ◽  
Rate Determining Step

Pyrolysis of benzoyl bromide in the presence of excess of toluene has been investigated. It has been shown that the rate-determining step is the unimolecular dissociation C 6 H 5 . CO. Br → C 6 H 5 . CO + Br, followed by the rapid decomposition of benzoyl radicals C 6 H 5 . CO → C 6 H 5 ⋅ + CO. Bromine atoms and phenyl radicals seem to be removed from the system by the reactions C 6 H 5 . CH 3 + Br → C 6 H 5 . CH 2 ⋅ + HBr and C 6 H 5 . CH 3 + Ph ⋅→ C 6 H 5 . CH 2 ⋅ + C 6 H 6 . The activation energy of the rate-determining dissociation process has been estimated using the least square method at 57⋅0 kcal/mole and has been identified with D (C 6 H 5 ⋅ CO-Br). Thus, having D (C 6 H 5 ⋅ CO-Br) = 57⋅0 kcal/mole, the heat of formation of benzoyl radicals has been calculated at ∆ H f (C 6 H 5 . CO) = 15⋅6 kcal/mole, and consequently the values for various bond dissociation energies of the type D (C 6 H 5 . CO- X ) have been derived.

Relationship between bond dissociation energies and activation energies for bond scission reactions

1994 ◽  
Vol 26 (1) ◽  
pp. 211-217 ◽  
Author(s):  
G. P. Smith ◽  
J. A. Manion ◽  
M. J. Rossi ◽  
A. S. Rodgers ◽  
D. M. Golden
Keyword(s):  
Activation Energies ◽  
Bond Dissociation Energies ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Bond Scission

scholarly journals Unimolecular Fragmentation Properties of Thermometer Ions from Chemical Dynamics Simulations

2020 ◽  
Author(s):  
Abdul Malik ◽  
Riccardo Spezia ◽  
William L. Hase
Keyword(s):  
Internal Energy ◽  
Rate Constants ◽  
Activation Energies ◽  
Bond Dissociation Energies ◽  
Excitation Energies ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Thermometer Ions ◽  
Dynamics Simulations ◽  
Threshold Energies

Thermometer ions are widely used to calibrate the internal energy of the ions produced by electrospray ionization in mass spectrometry. Commonly used ions are benzylpyridinium ions with different substituents. More recently benzhydrylpyridinium ions were proposed for their lower bond dissociation energies. Direct dynamics simulations using M06-2X/6-31G(d), DFTB, and PM6-D3 are performed to characterize the activation energies of two representative systems; para-methyl-benzylpyridinium ion (p-Me-BnPy+) and methyl,methylbenzhydrylpyridinium ion (Me,Me-BhPy+). The theoretical bond dissociation energies match closely with the experiment. Simulation results are used to calculate rate constants for the two systems. These rate constants and their uncertainties are used to find the Arrhenius activation energies and RRK fitted threshold energies which give reasonable agreement with calculated bond dissociation energies at the same level of theory. There is only one fragmentation mechanism observed for both systems, which involves C-N bond dissociation via a loose transition state, to generate either benzylium or benzhydrylium ion and a neutral pyridine molecule. For p-Me-BnPy+ using DFTB and PM6-D3 the formation of tropylium ion, from rearrangement of benzylium ion, was observed but only at higher excitation energies and for longer simulation times. These observations suggest that there is no competition between reaction pathways that could affect the reliability of internal energy calibrations.

scholarly journals Unimolecular Fragmentation Properties of Thermometer Ions from Chemical Dynamics Simulations

2020 ◽  
Author(s):  
Abdul Malik ◽  
Riccardo Spezia ◽  
William L. Hase
Keyword(s):  
Internal Energy ◽  
Rate Constants ◽  
Activation Energies ◽  
Bond Dissociation Energies ◽  
Excitation Energies ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Thermometer Ions ◽  
Dynamics Simulations ◽  
Threshold Energies

Thermometer ions are widely used to calibrate the internal energy of the ions produced by electrospray ionization in mass spectrometry. Commonly used ions are benzylpyridinium ions with different substituents. More recently benzhydrylpyridinium ions were proposed for their lower bond dissociation energies. Direct dynamics simulations using M06-2X/6-31G(d), DFTB, and PM6-D3 are performed to characterize the activation energies of two representative systems; para-methyl-benzylpyridinium ion (p-Me-BnPy+) and methyl,methylbenzhydrylpyridinium ion (Me,Me-BhPy+). The theoretical bond dissociation energies match closely with the experiment. Simulation results are used to calculate rate constants for the two systems. These rate constants and their uncertainties are used to find the Arrhenius activation energies and RRK fitted threshold energies which give reasonable agreement with calculated bond dissociation energies at the same level of theory. There is only one fragmentation mechanism observed for both systems, which involves C-N bond dissociation via a loose transition state, to generate either benzylium or benzhydrylium ion and a neutral pyridine molecule. For p-Me-BnPy+ using DFTB and PM6-D3 the formation of tropylium ion, from rearrangement of benzylium ion, was observed but only at higher excitation energies and for longer simulation times. These observations suggest that there is no competition between reaction pathways that could affect the reliability of internal energy calibrations.

A study of the C 2 H 4 +HCl=C 2 H 5 Cl and C 2 H 4 +HBr=C 2 H 5 Br equilibria

1953 ◽  
Vol 216 (1126) ◽  
pp. 361-374 ◽  
Keyword(s):  
Equilibrium Constants ◽  
Entropy Change ◽  
Heat Of Formation ◽  
Ethyl Chloride ◽  
Ethyl Bromide ◽  
Bond Dissociation Energies ◽  
Kcal Mole ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Heat Of Dissociation

The equilibrium constants of the two reactions C 2 H 4 + H X = C 2 H 5 X , where X = Cl or Br, have been measured for X = Cl from 449 to 491° K, and for X = Br from 515 to 573° K, The methods of preparing and purifying the substances used, of carrying out the analyses and of determining the equilibrium constants have been described. The results for the ethyl chloride equilibrium were combined with calculations of the entropy change using Gordon & Giauque’s barrier height in ethyl chloride of 3700 cal/mole to obtain a value for the heat content change. The value for this, corrected to 298° K, is 17·1 kcal/mole. This leads to a heat of formation of ethyl chloride of – 26·7 and a heat of dissociation of the C—Cl bond in ethyl chloride of 80·9 kcal/mole. For the ethyl bromide equilibrium, the entropy change was calculated using barrier heights in ethyl bromide of 3000, 4000 and 5000 cal/mole. Using the entropy changes calculated it was concluded that the heat of reaction, corrected to 298° K, is within 0·3 kcal/mole of 19·1. This leads to a heat of formation of ethyl bromide of – 15·3 and a heat of dissociation of the C—Br bond in ethyl bromide of 67·2 kcal/mole. The two bond dissociation energies have been incorporated in the recent tables of Mortimer, Pritchard & Skinner listing such energies. The significance of the values for the bond dissociation energies in the series of RX molecules, where R = Me, Et, n-Pr, n-Bu, iso-Pr and tert.-Bu , and X = H, Cl and Br have been discussed.

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