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.

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.

scholarly journals Experimental bond dissociation energies of benzylpyridinium thermometer ions determined by threshold-CID and RRKM modeling

2017 ◽  
Vol 417 ◽  
pp. 69-75 ◽  
Author(s):  
David Gatineau ◽  
Antony Memboeuf ◽  
Anne Milet ◽  
Richard B. Cole ◽  
Héloïse Dossmann ◽  
...  
Keyword(s):  
Bond Dissociation Energies ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Thermometer Ions

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 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.

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