Electronic Correlation in Molecules. III. The Paraffin Hydrocarbons<sup>1</sup>

Pitzer, Kenneth S.; Catalano, Edward

doi:10.1021/ja01600a006

Cited by 106 publications

(58 citation statements)

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“…As regards the CC bonds, however, eq. [13] commands the use of genuine eCC1s, whose values range from 69.63 to -74.5 kcal mol-' for the alkanes studied in this paper.5 Their validity is illustrated by the quality of calculated D*cc's (Table 7). A clarification concerning reorganization energies can now be given -a problem conveniently approached by an examination of CH bonds which are not equivalent in the hydrocarbon, but whose dissociation yields the same final products.…”

Section: Leading Terms Governing CC and Ch Bond Dissociationsmentioning

confidence: 90%

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Charge distributions and chemical effects. XLIII. Bond dissociation energies and radical formation

Fliszár¹,

Minichino²

1987

Can. J. Chem.

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SANDOR FLISZAR and CAMILLA MINICHINO. Can. J. Chem. 65, 2495 (1987).The problem of bond dissociation, RlR2 4 R I . + R2., is addressed from the viewpoint that the fragments, R1 and R2, may not be individually electroneutral in the host molecule, whereas the corresponding radicals certainly are. The mutual charge neutralization of R, by R2 during the cleavage of the bond linking R1 to R2 is described by an expression featuring only molecular ground-state properties. This expression translates directly into a new energy formula for the dissociation energy, D *(RIR2) = e(R1R2) + CNE -E*nb + RE(RI) + RE(R2), where both the molecule and the radicals are taken at their potential minimum.The charge neutralization energy, CNE, profoundly affects the relationship between the dissociation (D*) and contributing bond energy (E), i.e., the energy in the unperturbed molecule. Nonbonded interactions between R l and R2, E*nb, are almost negligible. The reorganizational energy, RE, measures the energy difference between R . and the corresponding electroneutral group found in the symmetric molecule RR. Numerical applications to alkanes reveal an important cancellation of individual CNE terms accompanying the mutual charge neutralization of alkyl groups during the cleavage of CC bonds, i.e., CNE -E*,, = 0. Theoretical eCC's lead to valid CC bond dissociation energies. In CH bond dissociations, on the other hand, the sum ECH + CNE remains nearly constant although individual eCH's may differ from one another by as much as 6 kcal mol-'. The concept of chemical bond is fundamental to chemistry. It turns out that nonbonded interactions are minor (1, 2), Its energetic aspects are at the center of this study, both for -0.02-0.05% of AE*,, so that the study of AE*, essentially non-reacting molecules and for molecules undergoing bond reduces to a consideration of bond energies, AE", -2 E,;.cleavage.Under laboratory conditions, molecules contain vibrational, translational, and rotational energies which are not fairly partitionable among chemical bonds. For convenience, our analysis considers the molecules at their potential minimum, i.e., with reference to their hypothetical vibratiocless state at 0 K; the role of vibrational energies is treated as a separate problem. The measure for what holds the atoms together in a molecule is thus offered by the difference AE*, = energy of all the isolated ground-state atoms minus the ground-state energy of the molecule which is the energy required for breaking up that molecule into its constituent atoms. The atomization energy, AE*,, includes the annihilation of all interactions between atom pairs which are not chemically bonded to one another in the conventional sense, AE*nb, and the destruction of all chemical bonds ij, represented by their energies eij, i.e.,'Visiting Scientist on leave from: Dipartimento di Chimica, Facolta di Scienze, Via Mezzocannone 4, Napoli, 1-80134, Italia.We must now become familiar with the precise meaning of eij. It represents the part of the total atomization energy which...

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Section: Leading Terms Governing CC and Ch Bond Dissociationsmentioning

confidence: 90%

“…Theoretical foundation for this additivity, which has a long history (13), has been established (14). With the experimental data of Table 1, we obtain two sets of AE*,(R.) values.…”

Section: Numerical Applications: the Alkanes Thermochemical Datamentioning

confidence: 99%

Charge distributions and chemical effects. XLIII. Bond dissociation energies and radical formation

Fliszár¹,

Minichino²

1987

Can. J. Chem.

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“…In diesem Zusammenhang ist es sehr überraschend, dass wir typischerweise Die Londonsche Dispersion, die den attraktiven Teil des Van- vdW-Wechselwirkungen mit dem regelmäßigen Verhalten der Siedepunkte der Alkane einführen, um ihre gegenseitige intermolekulare Anziehung zu erklären, gleichzeitig aber oft vergessen, dasselbe Konzept intramolekular anzuwenden, beispielsweise um die hçhere Stabilität verzweigter gegenüber linearen Alkanen zu verstehen (siehe Abschnitt 2.2). Bereits 1956 zeigten Pitzer und Catalano,d ass die Isomerisierungsenergie zwischen verzweigten und linearen Alkanen anhand der Dispersionsenergie erklärbar ist; [10] sie kamen zu dieser zunächst überraschenden Schlussfolgerung durch ihre Erkenntnis,d ass das anomale Verhalten der Dissoziationsenergien der Dihalogene nicht nur auf Unterschiede in der Elektronenpaar-Repulsion (Pauli-Repulsion) zurückzufüh-ren ist, sondern auch auf unterschiedlich starke Anziehung durch die LD,die am stärksten für Cl 2 ist (und um den Faktor fünf stärker als in F 2 ,d as das am wenigsten polarisierbare Halogen ist). [11] Obwohl er ein Harte-Kugel-Modell nutzte (bei Berücksichtigung von Londonscher Dispersion würde man wohl von einem Weiche-Kugel-Modell sprechen) und Hybridisierungsunterschiede ignorierte,p ostulierte Bartell 1959, dass "intramolecular van der Waals forces may be even more important than effects of hybridization and conjugation or hyperconjugation in governing bond angles,bond distances, energies of isomerization and hydrogenation, and bending vibrations of molecules" [12] {intramolekulare vdW-Kräfte wichtiger sein kçnnten als die Effekte von Hybridisierung, Konjugation oder Hyperkonjugation bei der Ausprägung von Bindungswinkeln, Bindungslängen, Isomerisierungs-und Hydrierungsenergien sowie bei Beugeschwingungen von Molekülen}.…”

Section: London'sche Dispersion -Z Uu Nrecht Unterschätztunclassified

“…[22] Es gibt auch Hinweise,d ass die Eigenschaften eher polarer Systeme wie ionischer Flüssigkei-ten [23] oder (anorganischer) kationischer Komplexe [24] entscheidend von Dispersionswechselwirkungen beeinflusst werden. Dies gilt genauso für die relativen Energien von Konformeren [25] und Wasserstoffbrückennetzwerken, [26] die Rotationsbarrieren von Alkanen [27] (Protobranching), [10,28] die 1,3-Allylspannung, [29] den Korsetteffekt [30] und seine Erweiterung [31] sowie die weitverbreitete Annahme,d ass eine tert-Butylgruppe nur repulsiv wirkt. [32] Dennoch wurden viele dieser Wechselwirkungen mithilfe alternativer Bindungsmodelle erläutert.…”

Section: à6unclassified

London’sche Dispersionswechselwirkungen in der Molekülchemie – eine Neubetrachtung sterischer Effekte

2015

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Die London’sche Dispersion, die den attraktiven Teil des Van‐der‐Waals‐Potentials beschreibt, wurde lange als Element struktureller Stabilität in der molekularen Chemie unterschätzt. Als solches beeinflusst sie auch entscheidend die chemische Reaktivität und Katalyse. Ihre Vernachlässigung ist auf die Annahme zurückzuführen, dass die Dispersionswechselwirkung schwach sei, was nur für eine einzelne paarweise Wechselwirkung zweier Atome stimmt. Für Strukturen zunehmender Größe kann die gesamte Dispersionsstabilisierung mehrere zehn kcal mol−1 betragen. Dieser Aufsatz soll die Wichtigkeit inter‐ und intramolekularer Dispersion anhand von Beispielen für die erste Vollperiode verdeutlichen. Die Synergie aus Experiment und Theorie hat ein Niveau erreicht, auf dem Dispersionseffekte sehr genau verstanden werden können. Als Konsequenz daraus werden wir wohl unser Verständnis bezüglich sterischer Hinderung und stereoelektronischer Effekte überdenken müssen. Die Quantifizierung von Dispersionsenergiedonoren wird unsere Fähigkeiten verbessern, komplexe molekulare Strukturen und Katalysatoren zu entwickeln.

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“…It is fortunate that ZPE + (HT -Ho) energies can often be constructed to a good approximation by means of additivity rules (1). Theoretical foundation for this additivity, which has a long history (2), has been established (3). In the following, we calculate ZPE + (HT -Ho) energies from spectroscopic data and examine how these results can be related to structural features.…”

Section: Introductionmentioning

confidence: 99%

Structure dependent regularities of zero-point plus heat content energies in organic molecules

Fliszár¹,

Poliquin²,

Badilescu³

et al. 1988

Can. J. Chem.

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A representative collection of heat content plus zero-point energies deduced in the harmonic oscillator approximation suggests a number of simple additivity rules which allow ZPE + (HT -Ho) to be related to structural features. Accurate evaluations are obtained for alkanes, alkenes, alkynes, cycloalkanes, chloroalkanes, and amines, as well as for large and small cycloalkanes in which CH2 is replaced by 0 . IntroductionIn our endeavour to understand the physics governing the energy of a molecule, traditional quantum mechanical energy minimization ends up describing a molecule at equilibrium, at its potential minimum. Thermochemistry, on the other hand, offers energy data (e.g., standard enthalpies of formation) for molecules possessing vibrational, rotational, and translational energies. This is where the problem lies. Vibrational energies are usually not as readily available as desired, thus rendering bona-fide comparisons between theory and experiment difficult, in spite of a wealth of thermochemical information. Indeed, the spectroscopic determination of the required complete sets of fundamental vibrational frequencies is usually far from being trivial, hence our interest in alternate rules which would allow the construction of reliable vibrational energies in a simple manner.The sum of zero-point (ZPE) plus heat content (HT -Ho)

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Electronic Correlation in Molecules. III. The Paraffin Hydrocarbons¹

Cited by 106 publications

References 0 publications

Charge distributions and chemical effects. XLIII. Bond dissociation energies and radical formation

Charge distributions and chemical effects. XLIII. Bond dissociation energies and radical formation

London’sche Dispersionswechselwirkungen in der Molekülchemie – eine Neubetrachtung sterischer Effekte

Structure dependent regularities of zero-point plus heat content energies in organic molecules

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Electronic Correlation in Molecules. III. The Paraffin Hydrocarbons1

Cited by 106 publications

References 0 publications

Charge distributions and chemical effects. XLIII. Bond dissociation energies and radical formation

Charge distributions and chemical effects. XLIII. Bond dissociation energies and radical formation

London’sche Dispersionswechselwirkungen in der Molekülchemie – eine Neubetrachtung sterischer Effekte

Structure dependent regularities of zero-point plus heat content energies in organic molecules

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Electronic Correlation in Molecules. III. The Paraffin Hydrocarbons¹