Properties of atoms and bonds in hydrocarbon molecules

Bader, R. F. W.; Tang, Ting Hua; Tal, Yoram; BIEGLER-KOENIG, F. W.

doi:10.1021/ja00368a004

Cited by 227 publications

(148 citation statements)

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“…[35][36][37] In this way, a bond line is found for each H-bond-type interaction, with the electron density at the corresponding bond critical point being much larger for the O-H‚ ‚ ‚O interactions in pyridine-2,3-and pyridine-3,4-dicarboxylic acids (0.0616 and 0.0547 au, respectively) as compared with the corresponding values found for the similar O-H‚ ‚ ‚O interactions in ortho-substituted methoxyphenols 34 whose average values amount to a mere 0.0214 au.…”

supporting

confidence: 42%

Thermochemical and Theoretical Studies of Dimethylpyridine-2,6-dicarboxylate and Pyridine-2,3-, Pyridine-2,5-, and Pyridine-2,6-dicarboxylic Acids

et al. 2005

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The standard (p°) 0.1 MPa) molar enthalpies of formation for gaseous pyridine-2,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, and dimethylpyridine-2,6-dicarboxylate were derived from the standard molar enthalpies of combustion, in oxygen, at T ) 298.15 K, measured by static bomb combustion calorimetry, and the standard molar enthalpies of sublimation, at 298.15 K, measured by Calvet microcalorimetry: pyridine-2,5-dicarboxylic acid, -(580.6 ( 5.0) kJ‚mol -1 ; pyridine-2,6-dicarboxylic acid, -(608.0 ( 6.1) kJ‚mol -1 ; dimethylpyridine-2,6-dicarboxylate, -(562.4 ( 4.2) kJ‚mol -1 . The enthalpy of formation for crystalline pyridine-2,3-dicarboxylic acid was also derived from combustion calorimetry measurements as -(733.1 ( 2.0) kJ‚mol -1 . In addition, theoretical calculations using the density functional theory and the B3LYP/6-311G** hybrid exchange-correlation energy functional have been performed for these molecules in order to obtain the most stable geometries and to access their relative stabilities. The good correlation obtained between experimental and theoretical results allowed the estimation of the enthalpy of sublimation for pyridine-2,3-dicarboxylic acid.

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supporting

confidence: 42%

Thermochemical and Theoretical Studies of Dimethylpyridine-2,6-dicarboxylate and Pyridine-2,3-, Pyridine-2,5-, and Pyridine-2,6-dicarboxylic Acids

et al. 2005

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“…As ε approaches to zero, the bond tends to be single or triple, i.e., completely symmetrical to interatomic axis. 29,[46][47][48] The QTAIM bond order 30,55 is obtained from its relation with the charge density in the BCP (ρ b ) of the corresponding CC bond {n = exp[A(ρ b -B)]}. The atomic dipole moment [M 1 (Ω)] measures the magnitude and direction of the electron cloud of the atom in relation with its nucleus.…”

Section: Rationalesupporting

confidence: 49%

Identification of carbonium and carbenium ions by QTAIM

Firme¹,

Antunes²,

Esteves³

2009

J. Braz. Chem. Soc.

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A ferramenta de Gassman-Fentiman da demanda crescente de elétrons foi usada para identificar íons carbênios e íons carbônios. Contudo, devido ao seu entendimento ambíguo, ela foi pivô de uma disputa histórica. Nós aplicamos a metodologia da Teoria Quântica de Átomos em Moléculas -QTAIM -para caracterizar íons carbênios e íons carbônios de uma forma mais eficaz e mais fácil. Essa metodologia pode ser usada para avaliar se um carbocátion é clássico ou não. Além disso, é possível classificar um conjunto de íon carbônio na ordem de magnitude da deslocalização σ, ou π. Há poucas diferenças entre os resultados de nosso modelo baseado na QTAIM e da ferramenta de Gassman-Fentiman. Contudo, diferentemente da ferramenta de Gassman-Fentiman, os cátions 7-anisol-7-norbornenila e 2-anisol-2-norbornila são não-clássicos, embora sejam os menos íons não-clássicos em seus conjuntos correspondentes de cátions estudados.The Gassman-Fentiman tool of increasing electron demand was used to identify carbonium and carbenium ions. Nonetheless, due to its ambiguous understanding, it was pivot of a historical dispute. We applied the Quantum Theory of Atoms in Molecules (QTAIM) metodology to characterize the carbonium and carbenium ions on an easier and more effective way. By comparing selected topological information of reference carbenium ions the QTAIM metodology can be used to evaluate whether a carbocation is classical or not. In addition, it is possible to rank a set of carbonium ions in order of their corresponding σ or π delocalization. There are few differences between our QTAIM-based model and Gassman-Fentiman tool. Unlike Gassman-Fentiman tool results, 7-anisyl-7-norbornenyl and 2-anisyl-2-norbornyl cations are non-classical, although they are the least nonclassical ions in their corresponding set of studied cations.Keywords: norbornyl cation, norbornenyl cation, QTAIM, carbonium ion, carbenium ion IntroductionIn 1949 Winstein and Trifan 1,2 postulated the assistance of σ electron delocalization to account for the large rate differences in acetolysis of exo-and endo-2-norbornyl brosilates. On the other hand, Brown 3,4 attributed these differences to steric effects. Thereafter, heated debates on nature of norbornyl cation, named the nonclassical ion controversy, took place.3-5 Nonetheless, experimental evidences 6-9 indicated that norbornyl cation had no trivalent carbenium center characteristic of a classical ion. Eventually, the nonclassical nature 10 of the hypercoordinate norbornyl cation, characterized by delocalized σ electrons in a threecenter two-electron (3c-2e) bonding, was proved. 11Carbenium and carbonium ions, formerly named classical and nonclassical ions, respectively, can be identified by an index developed by Schleyer and collaborators 12 based on the total 13 C NMR chemical shift difference between a carbocation and the corresponding neutral hydrocarbon. In the classical trivalent carbocations the chemical shift difference, ∆δ, is more than 350 ppm while in nonclassical carbocations ∆δ < 100 ppm.Gassman and Fent...

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“…This indicates a weakening of the bond, which is reflected by the increase in the F-H distance in going from the protonated mono-to trifluorinated acetones. This is similar to the relationship, noted above, between p(r,) and the CC bond length (9). Note that for a X-Y bond where X * Y, the bond critical point (solid circle) in a molecular graph is shifted in accord with the transfer of electrons between atoms (7).…”

Section: Methodsmentioning

confidence: 39%

“…The magnitude of the charge density at a bond critical point, p(r,), provides a measure of the bond strength (8). In fact, Bader et al (9) have shown that the bond-length -bond-order relationship of CC bonds in Hiickel theory may be generalized to include a variety of hydrocarbons. Their conclusion is based on the observation that the value of the total charge density at a bond critical point is characteristic of a bond of a given formal order.…”

Section: Introductionmentioning

confidence: 42%

Analysis of intramolecular hydrogen bonding in terms of the topological properties of the charge density. The protonated fluoroacetones

Choi¹,

Boyd²

1986

Can. J. Chem.

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. 64, 2042 (1986). A new method for the analysis of intramolecular hydrogen bonding is proposed and applied to the equilibrium structures of the protonated fluoroacetones. The method, based on a theory of molecular structure due to Bader, uses the topological properties of the charge density to elucidate the types of interactions within a molecule of interest. The calculations show a strong basis set dependence. In particular, the STO-3G optimized geometries exhibit intramolecular hydrogen bonding between a fluorine substituent and the carbonyl proton, whereas some calculations with geometries optimized at the 4-31G and 6-31G* levels indicate a direct bonding interaction between the fluorine and oxygen atoms. Two types of catastrophe point, namely conflict and bifurcation, are possible in protonated monofluoroacetone. Only the latter was located in the present calculations.

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Properties of atoms and bonds in hydrocarbon molecules

Cited by 227 publications

References 0 publications

Thermochemical and Theoretical Studies of Dimethylpyridine-2,6-dicarboxylate and Pyridine-2,3-, Pyridine-2,5-, and Pyridine-2,6-dicarboxylic Acids

Thermochemical and Theoretical Studies of Dimethylpyridine-2,6-dicarboxylate and Pyridine-2,3-, Pyridine-2,5-, and Pyridine-2,6-dicarboxylic Acids

Identification of carbonium and carbenium ions by QTAIM

Analysis of intramolecular hydrogen bonding in terms of the topological properties of the charge density. The protonated fluoroacetones

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