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

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.

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Unimolecular Fragmentation Properties of Thermometer Ions from Chemical Dynamics Simulations

10.26434/chemrxiv.12369059 ◽

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.

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

Canadian Journal of Chemistry ◽

10.1139/v70-463 ◽

1970 ◽

Vol 48 (17) ◽

pp. 2745-2754 ◽

Cited By ~ 23

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.

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Unimolecular Fragmentation Properties of Thermometer Ions from Chemical Dynamics Simulations

10.26434/chemrxiv.12369059.v1 ◽

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.

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Activation energies for the dissociation of diatomic molecules are less than the bond dissociation energies

Accounts of Chemical Research ◽

10.1021/ar50058a002 ◽

1972 ◽

Vol 5 (10) ◽

pp. 327-335 ◽

Cited By ~ 76

Author(s):

Harold Johnston ◽

John Birks

Keyword(s):

Diatomic Molecules ◽

Activation Energies ◽

Bond Dissociation Energies ◽

Bond Dissociation ◽

Dissociation Energies

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Unimolecular Fragmentation Properties of Thermometer Ions from Chemical Dynamics Simulations

10.26434/chemrxiv.12369059.v3 ◽

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.

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

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1953.0151 ◽

1953 ◽

Vol 219 (1138) ◽

pp. 341-352 ◽

Cited By ~ 9

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.

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