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Ab initio determination of the equilibrium geometry and vibrational frequencies of borazine
No full textJournal of Molecular Structure: THEOCHEM
Volume 236, Issue 1-2, 1 November 1991, Pages 29-39
Ab initio determination of the equilibrium geometry and vibrational frequencies of borazine (Article)
Ramondo, F., Portalone, G., Bencivenni, L.
Dipartimento di Chimica, Universitá degli Studi di Roma La Sapienza, P. le A. Moro 5, 00185 RomaItaly
View references (20)
Abstract
The equilibrium structure of borazine, B3N3H6, has been optimized at the HF-SCF level using the 6-31G, 6-31G*, 6-31 + G*, 6-31 + + G**, 6-311G**, DZP and TZP basis sets and at the secondorder Moeller-Plesset perturbation theory, with all orbitals active, with the 6-31G* basis set (MP2/ 6-31G*). The D3h symmetry conformation is established to be, at all the adopted levels of theory, the global minimum of the molecule. The planar structure has been studied employing several basis sets and the effects of basis set extension and of polarization d-functions on the molecular geometry are discussed. The bond distances and the ring angles of borazine determined at the MP2/6-31G* level are, (BN) 1.430 Å, (BH) 1.197 Å, (NH) 1.012 Å, (BNB) 122.9° and (NBN) 117.1°. HF-SCF and MP2/6-31G* vibrational frequencies have been calculated in the harmonic approximation and the vibrational spectrum of borazine is reassigned accordingly. © 199
Group Electronegativities from Benzene Ring Deformations: A Quantum Chemical Study
No full textWe propose a new scale of group electronegativities, derived from benzene ring deformations in Ph-X
molecules. A recent analysis of such deformations (Campanelli, A. R.; Domenicano, A.; Ramondo, F. J.
Phys. Chem. A 2003, 107, 6429) has shown that two orthogonal linear combinations of the internal ring
angles, termed SE and SR, are directly related to the electronegativity and resonance effects of the substituent,
respectively. In the present paper, we show that SE increases linearly with the electronegativity of X within
each of the first two rows of the periodic table, acting as a sensitive indicator of the polarity of the Ph-X
bond. By using SE values from ab initio quantum chemical calculations, we have derived the electronegativities
of 100 organic and inorganic groups. Nonbonded interactions with the ortho hydrogens and carbons may
fictitiously alter the electronegativity of a group; in most cases, however, they are easily eluded by changing
the conformation of the substituent with respect to the benzene ring. Although the atom directly linked to the
ring tends to dominate the electronegativity of a group, the role of its adjacent atoms is also important. Their
effect depends markedly on the nature of chemical bonding and electron density distribution within the group
Marriage record of Gonzalez, Ramondo and Jerez, Matilda
No full textMarriage license for Ramondo Gonzalez and Matilda Jerez. Fred M. Meyer was the Notary Public
Group electronegativities from benzene ring deformations: a quantum chemical study
No full textWe propose a new scale of group electronegativities, derived from benzene ring deformations in Ph-X molecules. A recent analysis of such deformations (Campanelli, A. R.; Domenicano, A.; Ramondo, F. J. Phys. Chem. A 2003, 107, 6429) has shown that two orthogonal linear combinations of the internal ring angles, termed SE and SR, are directly related to the electronegativity and resonance effects of the substituent, respectively. In the present paper, we show that SE increases linearly with the electronegativity of X within each of the first two rows of the periodic table, acting as a sensitive indicator of the polarity of the Ph-X bond. By using SE values from ab initio quantum chemical calculations, we have derived the electronegativities of 100 organic and inorganic groups. Nonbonded interactions with the ortho hydrogens and carbons may fictitiously alter the electronegativity of a group; in most cases, however, they are easily eluded by changing the conformation of the substituent with respect to the benzene ring. Although the atom directly linked to the ring tends to dominate the electronegativity of a group, the role of its adjacent atoms is also important. Their effect depends markedly on the nature of chemical bonding and electron density distribution within the grou
La población urbana Argentina 1960 a 1991 revisión metodológica y resultados estadísticos
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