A contribution to gas phase ionization of para-hydroxybenzoic acid: An LCAO-MO-SCF treatment

1988 ◽  
Vol 53 (4) ◽  
pp. 665-670 ◽  
Author(s):  
Stanislav Böhm ◽  
Josef Kuthan
Keyword(s):  
Gas Phase ◽  
Basis Set ◽  
Hydroxybenzoic Acid ◽  
Carboxylic Group ◽  
Mo Calculations ◽  
Gas Phase Acidity ◽  
Mndo Calculations ◽  
Phenolic Group ◽  
Semi Empirical ◽  
Lcao Mo

By means of the ab initio MO calculations using the STO-3G basis set augmented with diffuse p functions accompanied by semi-empirical MNDO calculations, it is demonstrated that the carboxylic group ionization in the isodesmy (A), X = p-OH, is energetically preferred to the phenolic group ionization in the process (B). The reasons of the earlier incorrect interpretations regarding the gas phase acidity of p-hydroxybenzoic acid (a,s-II) are discussed.

The choice of the optimal basis set for the 4th period atoms from Cu to Kr in SCF LCAO MO calculations on complex inorganic molecules

1973 ◽  
Vol 13 (4) ◽  
pp. 705-707
Author(s):  
S. P. Dolin ◽  
B. F. Shchegolev ◽  
N. M. Klimenko ◽  
E. L. Rozenberg ◽  
M. E. Dyatkina
Keyword(s):  
Basis Set ◽  
Mo Calculations ◽  
Optimal Basis ◽  
Inorganic Molecules ◽  
Lcao Mo

Photoelectron Spectroscopy of Heterocycles. Polypyridines

1978 ◽  
Vol 33 (2) ◽  
pp. 247-248 ◽  
Author(s):  
I. Novak ◽  
L. Klasinc
Keyword(s):  
Gas Phase ◽  
Photoelectron Spectroscopy ◽  
Lone Pair ◽  
Mo Calculations ◽  
Factors Influencing ◽  
Nitrogen Lone Pair ◽  
Lcao Mo

The photoelectron (PE) spectra of 2,2′-bipyridine 1, 2,2′:6′,2″-terpyridine 2, and 2,2′,2″,2‴-tetrapyridine 3 have been measured using He I radiation. For 1-3 standard SCF LCAO MO calculations wer also performed. Comparison of PE spectra and these calculations allowed the assignment of π-ionizations and indirectly also the nitrogen lone pair ionizations in 1-3. Factors influencing the conformations of 1-3 in the gas phase are also mentioned.

Photoelectron Spectroscopy of Heterocycles. Dipyridylethylenes

1977 ◽  
Vol 32 (8) ◽  
pp. 886-889
Author(s):  
I. Novak ◽  
L. Klasinc ◽  
J. V. Knop
Keyword(s):  
Gas Phase ◽  
Photoelectron Spectroscopy ◽  
Lone Pair ◽  
Mo Calculations ◽  
Trans Conformation ◽  
Nitrogen Lone Pair ◽  
Lcao Mo

AbstractThe photoelectron (PE) spectra of 1,2-di-(2-pyridyl)-ethylene 1, 1-(2-pyridyl)-2-(3-pyridyl)- ethylene 2, 1-(2-pyridyl) -2- (4-pyridyl) -ethylene 3 and 1,2-di-(4-pyridyl)-ethylene 4 all in their trans conformation have been measured using He I radiation. For 1 - 4 standard SCF LCAO MO calculations were performed changing the angle of twist ϑ of the pyridine rings around their bonds to ethylene conrotatively from 0° to 60°. Comparison of PE spectra and these calculations allowed the assignment of all π-ionizations and indirectly also the nitrogen lone pair ionizations in 1 - 4 but not a determination of their conformation in the gas phase. There is only indication that ϑ in these molecules is rather small (ϑ<30°).

Atomic parameters for semi-empirical SCF-LCAO-MO calculations

1967 ◽  
Vol 7 (1) ◽  
pp. 32-40 ◽  
Author(s):  
J. M. Sichel ◽  
M. A. Whitehead
Keyword(s):  
Mo Calculations ◽  
Semi Empirical ◽  
Atomic Parameters ◽  
Lcao Mo

Hydrogen bonding of O—H and C—H hydrogen donors to Cl−. Results from mass spectrometric measurements of the ion–molecule equilibria RH + Cl− = RHCl−

1982 ◽  
Vol 60 (15) ◽  
pp. 1907-1918 ◽  
Author(s):  
M. A. French ◽  
S. Ikuta ◽  
P. Kebarle
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Gas Phase ◽  
Positive Charge ◽  
Equilibrium Constants ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Simple Relationship ◽  
Gas Phase Acidity ◽  
Carbon Acids

Equilibrium constants K1 for reaction [1] RH + Cl− = RHCl− in the gas phase were measured with a high pressure mass spectrometer under chemical ionization conditions. Data for some 40 compounds RH are presented. It is found that the binding free energies [Formula: see text] for RH = oxygen acids increase with the gas phase acidity of RH. The strongest bonds are formed with strong acids like HCO2H, CH3CO2H, and phenol. Water and alkyl alcohols give much weaker interactions. A simple relationship between gas phase acidity and binding free energy does not occur for RH = carbon acids. Carbon acids like cyclopentadiene, whose high gas phase acidity is largely due to charge derealization by conjugation in the completed anion, do not give Cl− adducts with stability commensurate with the acidity. A relationship between gas phase acidity and binding energy is found for carbon acids with carbonyl groups and for the substituted toluenes. Molecular orbital calculations with the STO-3G basis set provide insights to the bonding occurring in RHCl−. For all cases investigated, hydrogen bonding to Cl− provides the most stable structure. Generally the hydrogen bond occurs through the hydrogen which has the highest net positive charge. The hydrogen bond strength is found approximately proportional to this positive charge. Another proportionality is found between the charge transferred from Cl− to RH, on formation of RHCl−, and the strength of the hydrogen bond.

On the trustability of semi-empirical methods to the calculation of gas phase formation enthalpies of inorganic compounds containing heavy metals: tin borates

2017 ◽  
Author(s):  
Robson de Farias
Keyword(s):  
Heavy Metals ◽  
Gas Phase ◽  
Phase Formation ◽  
Inorganic Compounds ◽  
Formation Enthalpy ◽  
Computational Time ◽  
Gas Formation ◽  
Formation Enthalpies ◽  
Knudsen Effusion Mass Spectrometry ◽  
Semi Empirical

<p>In the present work, are calculated the gas formation enthalpies (SE; PM3 and PM6) for tin borates: SnB<sub>2</sub>O<sub>4</sub><sup> </sup>and Sn<sub>2</sub>B<sub>2</sub>O<sub>5</sub>. The calculated values are compared with experimental ones, obtained by Knudsen effusion mass spectrometry [3]. It is shown that SE methods, besides their lower computational time consuming can, indeed, provide reliable gas phase formation enthalpy values for inorganic compounds containing heavy metals.</p>

scholarly journals Experimental and Computational Studies on the Gas-Phase Acidity of 5,5-Dialkyl Barbituric Acids

2021 ◽  
Author(s):  
Juan Z. Dávalos-Prado ◽  
Javier González ◽  
Josep M. Oliva-Enrich ◽  
Emma J. Urrunaga ◽  
Alexsandre F. Lago
Keyword(s):  
Gas Phase ◽  
Computational Studies ◽  
Gas Phase Acidity
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