Studies of the variations in bond dissociation energies of aromatic compounds - II. Substituted bromobenzenes

1953 ◽  
Vol 219 (1138) ◽  
pp. 353-366 ◽  
Keyword(s):  
Benzene Ring ◽  
Bond Dissociation Energy ◽  
Aromatic Compounds ◽  
Frequency Factor ◽  
Bond Dissociation Energies ◽  
Kcal Mole ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Tentative Explanation ◽  
The Difference

The paper reports the effects of substituents on C— Br bond dissociation energy in substituted bromobenzenes. The following substituents introduced in various positions of benzene ring were investigated: F, Cl, Br, CH 3 , C 6 H 5 , CN and OH. In addition, the studies were extended to bromopyridines and bromothiophene. Assuming that the frequency factor is constant for the series of decompositions, the following values were obtained for the difference ∆ D = D ( Ph — Br) - D ( Ph s — Br), where Ph s Br denotes a molecule of substituted bromobenzene: substituent ∆D (kcal/mole) substituent ∆D (kcal/mole) p -F 0-5 m -C 6 H 5 0-8 p -Cl 0-6 o -C 6 H 5 2-7 m -Cl 1-0 p -CN 0-3 o -Cl 1-2 m -CN 0-8 p -Br 0-3 o -CN 0-6 o -Br 1-8 p -OH 3-9 P -CH 3 0-2 o -OH 3-8 m -CH 3 0-2 3-bromopyridine -5-0 o -CH 3 0-8 2-bromopyridine -0-6 p -C 6 H 5 0-2 2-bromothiophene 2-4 The significance of these results is discussed, and a tentative explanation of the observed effects is proposed.

The C—Br bond dissociation energy in halogenated bromomethanes

1951 ◽  
Vol 209 (1096) ◽  
pp. 110-131 ◽  
Keyword(s):  
Bond Dissociation Energy ◽  
Dissociation Energy ◽  
Methyl Bromide ◽  
Frequency Factor ◽  
Unimolecular Dissociation ◽  
Bond Dissociation Energies ◽  
Kcal Mole ◽  
Fast Reaction ◽  
Bond Dissociation ◽  
Dissociation Energies

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.

The C—Br bond dissociation energy in substituted benzyl bromides

1951 ◽  
Vol 209 (1096) ◽  
pp. 97-110 ◽  
Keyword(s):  
Bond Energy ◽  
Benzyl Bromide ◽  
Frequency Factor ◽  
Unimolecular Dissociation ◽  
Bond Dissociation Energies ◽  
Kcal Mole ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Rate Determining Step

The ‘toluene-carrier’ technique has been used for the determination of the C—Br bond dissociation energies in the substituted benzyl bromides: p -, m - and o -xylyl bromides; p -, m - and o -chlorobenzyl bromides; p - and m -bromobenzyl bromides; p - and m -nitrobenzyl bromides; and p - and m -nitrilebenzyl bromides. The rate-determining step of the decompositions of all these compounds is represented by the unimolecular dissociation processes ( s ) Ph s . CH 2 . Br → Ph s . CH 2 • + Br, ( s ) where Ph s . CH 2 . Br refers to the substituted benzyl bromide. Assuming that the frequency factor of the decomposition of each benzyl bromide is equal to the frequency factor of reaction ( u ) Ph . CH 2 . Br → Ph . CH 2 • + Br, ( u ) the differences in activation energies between E u and E s were calculated using the relation E u ─ E s = RT In ( k s / k u ); (I) k s and k u denote the unimolecular rate constants of reactions ( s ) and ( u ) respectively. Since E s and E u are equal to the C—Br bond dissociation energies in the substituted benzyl bromides and benzyl bromide itself, equation (I) yields the differences, ∆ D’ s, between D ( Ph . CH 2 —Br) and the values for D ( Ph s . CH 2 —Br). The calculated differences in the C—Br bond dissociation energies are listed below: substituted ∆ D substituted ∆ D benzyl bromides (kcal. /mole) benzyl bromides (kcal. /mole) o -chloro 0·9 m -methyl 0-0 m -chloro 0·1 p -methyl 1·4 p -chloro 0·4 m -nitro 2·1 m -bromo 0·3 p -nitro 1·1 p -bromo 0·3 m -nitrile 1·4 o -methyl 2·0 p -nitrile 0·7 The significance of these findings is discussed, and the effect of substitution on a bond energy is contrasted with the effect of ionic reactions.

H—N3 and CH3—N3 bond dissociation energies

1968 ◽  
Vol 46 (24) ◽  
pp. 3785-3788 ◽  
Author(s):  
Mervyn Chiang ◽  
Robert Wheeler
Keyword(s):  
Temperature Variation ◽  
Thermal Emission ◽  
Bond Dissociation Energies ◽  
Kcal Mole ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Heated Filament

The thermal emission of negative azide ions from a heated filament operating in gases of both HN3 and CH3N3 has been studied in a magnetron cell and the temperature variation of this current used to deduce the C—N bond dissociation energies in both molecules. Results indicate higher values than previous estimates. They are: D0(H—N3) = 90 ± 8 kcal/mole and D0(CH3—N3) = 88 ± 8 kcal/mole at 0°K.

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.

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.

Electron-impact study of some binary metal carbonyls

1967 ◽  
Vol 45 (6) ◽  
pp. 641-648 ◽  
Author(s):  
D. R. Bidinosti ◽  
N. S. McIntyre
Keyword(s):  
Mass Spectra ◽  
Major Ions ◽  
Heat Of Formation ◽  
Bond Dissociation Energies ◽  
Metal Carbonyls ◽  
Kcal Mole ◽  
Carbon Bond ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
The Mean

The mass spectra and appearance potentials for the major ions from Ni(CO)4, Fe(CO)5, Cr(CO)6, Mo(CO)6, W(CO)6, and V(CO)6 have been measured. Heats of formation have been calculated for 39 ions of the type M(CO)n+, where M = Ni, Fe, Cr, Mo, W, and V. The mean metal–carbon bond dissociation energies have been calculated for both the neutral molecules and the parent ions. From a comparison with the available thermochemical data for the neutral molecules it is concluded that the mean vanadium–carbon bond dissociation energy is 28 kcal/mole and the heat of formation of V(CO)6 vapor is − 204 kcal/mole.

scholarly journals Benchmark calculations for bond dissociation energies and enthalpy of formation of chlorinated and brominated polycyclic aromatic hydrocarbons

RSC Advances ◽  
2021 ◽  
Vol 11 (47) ◽  
pp. 29690-29701
Author(s):  
Shenying Xu ◽  
Quan-De Wang ◽  
Mao-Mao Sun ◽  
Guoliang Yin ◽  
Jinhu Liang
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Enthalpy Of Formation ◽  
Bond Dissociation Energy ◽  
Aromatic Hydrocarbons ◽  
State Of The Art ◽  
Bond Dissociation Energies ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Composite Methods ◽  
Polycyclic Aromatic

Benchmark calculations using state-of-the-art DFT functionals and composite methods for bond dissociation energy and enthalpy of formation of halogenated polycyclic aromatic hydrocarbons are performed.

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.

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