Modeling Gas-Phase Unimolecular Dissociation for Bond Dissociation Energies: Comparison of Statistical Rate Models within RRKM Theory

Kcal Mole ◽

Fast Reaction ◽

Bond Dissociation ◽

The pyrolyses of methyl bromide and of the halogenated bromomethanes, CH 2 CI. Br, CH 2 Br 2 , CHCl 2 .Br, CHBr 3 , CF 3 Br, CCI 3 . Br and CBr 4 , have been investigated by the ‘toluene-carrier' technique. It has been shown that all these decompositions were initiated by the unimolecular process R Br → R + Br. (1) Since all these decompositions were carried out in the presence of an excess of toluene, the bromine atoms produced in process (1) were readily removed by the fast reaction C 6 H 5 .CH 3 + Br → C 6 H 5 . CH 2 • + HBr. Hence, the rate of the unimolecular process (1) has been measured by the rate of formation of HBr. The C—Br bond dissociation energies were assumed to be equal to the activation energies of the relevant unimolecular dissociation processes. These were calculated by using the expression k ═ 2 x 10 13 exp (- D/RT ). The reason for choosing this particular value of 2 x 10 13 sec. -1 for the frequency factor of these reactions is discussed. The values obtained for the C—Br bond dissociation energies in the investigated bromomethanes are: D (C—Br) D (C—Br) compound (kcal./mole) compound (kcal./mole) CH 3 Br (67.5) CHBr 3 55.5 CH 2 CIBr 61.0 CF 3 Br 64.5 CH 2 Br 2 62.5 CCI 3 Br 49.0 CHCl 2 Br 53.5 CBr 4 49.0 The possible factors responsible for the variation of the C—Br bond dissociation energy in these compounds have been pointed out.

Negative Ion Mass Spectra, Electron Affinities, Gas Phase Acidities, Bond Dissociation Energies, and Negative Ion States of Cytosine and Thymine

The Journal of Physical Chemistry B ◽

10.1021/jp001553z ◽

2000 ◽

Vol 104 (32) ◽

pp. 7835-7844 ◽

Cited By ~ 51

Author(s):

Edward C. M. Chen ◽

Edward S. Chen

Keyword(s):

Gas Phase ◽

Mass Spectra ◽

Negative Ion ◽

Electron Affinities ◽

Bond Dissociation ◽

Thermochemistry of Elementary Actinide Sulfide Molecules: A Gas-Phase Study of Curium Sulfide

MRS Proceedings ◽

10.1557/proc-1264-z02-04 ◽

2010 ◽

Vol 1264 ◽

Author(s):

Cláudia C. L. Pereira ◽

Joaquim Marçalo ◽

John K. Gibson

Keyword(s):

Gas Phase ◽

Gas Phase Reactions ◽

General Applicability ◽

Molecular Systems ◽

Bond Dissociation ◽

Dissociation Energies ◽

Phase Study ◽

Fundamental Understanding ◽

Actinide Ions

AbstractExperiments to explore the reactivity and thermochemistry of elementary transuranium sulfide molecules have been initiated to expand the basis for a fundamental understanding of actinide bonding, and to enable the development of advanced theoretical methodologies which will be of general applicability to more complex molecular systems. Bimolecular gas-phase reactions between transuranium actinide ions and neutral reagents are employed to obtain thermochemical information. The initial actinide sulfide studies have focused on obtaining the 298 K bond dissociation energy for the CmS+ ion, D[Cm+-S] = 475±37 kJ mol-1; from this result and an estimate of IE[CmS] ≈ IE[CmO] + 0.5 eV, we obtain D[Cm-S] = 563±64 kJ mol-1. The bond dissociation energies, D[Cm+-S] and D[Cm-S] are approximately 200 kJ mol-1 and 150 kJ mol-1 lower than for the corresponding oxides, CmO+ and CmO. The nature of the bonding in the CmS+ ion appears to be generally similar to that in other oxophilic metal sulfides. Comparisons with previous bond dissociation energies reported for ThS and US may suggest a difference in the An-S bonds for these early actinide sulfides as compared with CmS.

Experimental and Theoretical Gas-Phase Acidities, Bond Dissociation Energies, and Heats of Formation of HClOx,x= 1−4

The Journal of Physical Chemistry A ◽

10.1021/jp100888k ◽

2010 ◽

Vol 114 (12) ◽

pp. 4086-4092 ◽

Cited By ~ 32

Author(s):

Matthew M. Meyer ◽

Steven R. Kass

Keyword(s):

Gas Phase ◽

Heats Of Formation ◽

Bond Dissociation ◽

Experimental and computational studies of deuterated ethanols: gas-phase acidities, electron affinities and bond dissociation energies

International Journal of Mass Spectrometry and Ion Processes ◽

10.1016/0168-1176(93)87096-b ◽

1993 ◽

Vol 123 (3) ◽

pp. 171-185 ◽

Cited By ~ 21

Author(s):

Thuy Thanh Dang ◽

Edwin L. Motell ◽

Michael J. Travers ◽

Eileen P. Clifford ◽

G. Barney Ellison ◽

...

Keyword(s):

Gas Phase ◽

Computational Studies ◽

Electron Affinities ◽

Bond Dissociation ◽

Acidities and homolytic bond dissociation energies of the αC—H bonds in ketones in DMSO

Canadian Journal of Chemistry ◽

10.1139/v90-266 ◽

1990 ◽

Vol 68 (10) ◽

pp. 1714-1718 ◽

Cited By ~ 68

Author(s):

Frederick G. Bordwell ◽

John A. Harrelson Jr

Keyword(s):

Gas Phase ◽

Radical Cations ◽

Bond Dissociation ◽

Dissociation Energies ◽

Oxidation Potentials ◽

Stabilization Energies ◽

Conjugate Bases

Equilibrium acidities in DMSO are reported for nine cycloalkanones, acetone, acetophenone, and 19 of their α-substituted derivatives. Oxidation potentials in DMSO for the conjugate bases of most of these ketones are also reported. Combination of these EOX(A−) and pKHA values gives estimates of the homolytic bond dissociation energies (BDEs) of the acidic C—H bonds in the ketones. The ΔBDEs, relative to the BDE of CH3-H, or a parent ketone, provide a measure of the radical stabilization energies (RSEs) of the corresponding radicals. The effects of successive α-Me and α-Ph substitutions on RSEs, relative to those of CH3COCH2-H or PhCOCH2-H, are similar to those reported in the gas phase for methane. The RSE for the MeĊHCOPh radical, relative to CH3• is 17 kcal/mol, which is smaller than the sum of the RSEs of the MeCH2• and PhCOCH2• radicals relative to CH3• (7 + 12 = 19), contrary to the prediction of the captodative postulate. When G in PhCOCH2G is PhCO, CH3CO, or CN the ΔBDEs (relative to PhCOCH2-H) are 0, 1, and 3 respectively; for MeCOCH2SO2Ph, PhCOCH2SO2Ph, and PhCOCH2NMe3+ the ΔBDEs are −5, −2, and −4, respectively. The BDEs in C5, C6, C7, C8, C10, and C12 cycloalkanones are within ±2.5 kcal/mol of that of 3-pentanone. Acetophenones bearing meta or para substituents all have BDEs of 93-94 kcal/mol. Ketone radical cations, [RCOR′]+•, appear to be superacids with estimated [Formula: see text] values below −25. Keywords: acidities, bond dissociation energies, ketones.