The structure and energetics of low-lying states of RCO and RNN free radicals

1977 ◽  
Vol 55 (5) ◽  
pp. 863-868 ◽  
Author(s):  
N. Colin Baird ◽  
Harish B. Kathpal
Keyword(s):  
Experimental Data ◽  
Free Radicals ◽  
Hydrogen Atom ◽  
Ab Initio ◽  
Open Shell ◽  
Basis Set ◽  
Basis Sets ◽  
Mo Calculations ◽  
Decomposition Products ◽  
Ab Initio Mo Calculations

The important geometrical variables in the structures of the lowest 2A′ and 2A′′ states of the free radicals HCO, CH3CO, NH2CO, HNN, and CH3NN have been determined by ab initio MO calculations using the STO-3G basis set. The energy differences between the states, and the energies of the radicals relative to their decomposition products and relative to their hydrogen atom addition products, are reported using both STO-3G and 4-31G basis sets in the restricted open-shell calculations. The trends in these results and their relation to available experimental data are discussed.

Abinitio MO predictions for the geometries and energies of the Σ and II states of some conjugated free radicals

1980 ◽  
Vol 58 (7) ◽  
pp. 733-738 ◽  
Author(s):  
N. Colin Baird ◽  
Kathleen F. Taylor
Keyword(s):  
Free Radicals ◽  
Nitrogen Atom ◽  
Configuration Interaction ◽  
Open Shell ◽  
Basis Set ◽  
Basis Sets ◽  
Energy Separation ◽  
Mo Calculations ◽  
Geometric Variables

Abinitio MO calculations are reported for the lowest Σ and Π doublet states of the radicals 1–10. Configuration interaction is included, using the restricted open-shell MO's as a base. The important geometric variables are optimized in calculations using the STO-3G basis set; in some cases energies and geometries are redetermined using the 4-31G basis. In most cases the energy separation between the Σ and Π doublet states is calculated to be small; the results are very dependent upon the basis set whenever the radical is localized upon a nitrogen atom. For radicals XYZ with different terminal groups, a valid prediction of the structure is obtained only if the basis set properly distinguishes between the π energies of X=Y and Y=Z bonds. Small basis sets appear to underestimate the π energy of carbonyl bonds, and thus are overbiased in favour of X=C—O••structures. Unsymmetrical structures are predicted for the Σ states of some radicals, even when the terminal groups are identical.

Sulfonamidyls, 4. Ab Initio MO Calculations on Sulfonyl and Carbonyl Substituted Aminyl Radicals

1981 ◽  
Vol 36 (2) ◽  
pp. 279-281 ◽  
Author(s):  
Herman Teeninga ◽  
Wim C. Nieuwpoort ◽  
Jan B. F. N. Engberts
Keyword(s):  
Ab Initio ◽  
Hyperfine Splitting ◽  
Relative Magnitude ◽  
Basis Set ◽  
Mo Calculations ◽  
Aminyl Radicals ◽  
Ab Initio Mo Calculations ◽  
Double Zeta ◽  
Double Zeta Basis ◽  
Ab Initio Mo

Abstract The relative magnitude of the nitrogen hyperfine splitting constants of sulfonamidyls and carboxamidyls is rationalized in terms of the results of ab initio MO calculations using the "double zeta" basis set of Roos and Siegbahn.

Orbital interactions. XII. Product studies and competition kinetic measurements of the Birch reduction of a series of hexahydrodimethanonaphthalenes and their interpretation in terms of orbital interactions through space and through bonds

1983 ◽  
Vol 36 (12) ◽  
pp. 2423 ◽  
Author(s):  
DD Chau ◽  
MN Paddon-Row ◽  
HK Patney
Keyword(s):  
Ab Initio ◽  
Anion Radical ◽  
Basis Set ◽  
Mo Calculations ◽  
Birch Reduction ◽  
Symmetry Constraint ◽  
Orbital Interactions ◽  
Ab Initio Mo Calculations ◽  
Ab Initio Mo ◽  
Anion Radicals

Relative rate constants for the Birch reduction (Li/liq. NH3/ButOH) of the three isomeric hexahydrodimethanonaphthalenes (3)-(5) and the octahydro analogues (10)-(13) were obtained and compared with those obtained for the reduction of norbornadiene and norbornene from an earlier study. Diene (5) was reduced almost 2000 times more rapidly than norbornene and 20000 times more rapidly than the monoene (13). Rate-enhancement factors for dienes (3) and (4) were less substantial but meaningful: 19 for (3) [compared with (10)] and 35 for (4) [compared with (12)]. These rate enhancements were attributed to the operation of π* orbital interactions through space in diene (5) and to the presence of π* orbital interactions through four bonds in dienes (3) and (4). The existence of a linear relationship between the natural logarithm of the rate of reduction of a substrate and its LUMO energy (obtained from either gas-phase electron affinities or ab initio MO calculations) supports this conclusion. The only-fair correlation of the above relationship was attributed to the neglect of other factors, such as the electronic structure and the geometry of the anion radical, which contribute to the overall rate of the Birch reduction. These two factors were explored by using PMO theory and ab initio MO calculations. In particular, full geometry optimizations (UHF, STO-3G basis set) on the anion radicals of norbornadiene (1) (C2v symmetry constraint) and norbornene (22) (Cs symmetry constraint) were carried out, and their geometries reported. Noteworthy is the strong pyramidalization of the olehic centres of (1) and (22) in the endo direction. These pyramidalizations explain the observed stereoselective exo protonation of the anion radical of (1), and also the much faster rate of reduction of (1) compared with (5), since the pyramidalization in the anion radical of (5) is such as to hinder protonation. The geometries of anion radicals appear to have a profound effect on rates, on stereoselectivity of protonation, and on the structures of the final products, and this is discussed in detail. The synthesis of the diene (3) is also described.

A Systematic DFT Study of Two Elementary Steps Involving Hydrogen Peroxide and the Hydroxyl Radical in the Fenton Reaction

2018 ◽  
Author(s):  
Danilo Carmona ◽  
David Contreras ◽  
Oscar A. Douglas-Gallardo ◽  
Stefan Vogt-Geisse ◽  
Pablo Jaque ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Hydroxyl Radical ◽  
Ab Initio ◽  
Fenton Reaction ◽  
Basis Set ◽  
Basis Sets ◽  
Dft Methods ◽  
Elementary Steps ◽  
Oxygen Oxygen ◽  
Complete Basis Set

The Fenton reaction plays a central role in many chemical and biological processes and has various applications as e.g. water remediation. The reaction consists of the iron-catalyzed homolytic cleavage of the oxygen-oxygen bond in the hydrogen peroxide molecule and the reduction of the hydroxyl radical. Here, we study these two elementary steps with high-level ab-initio calculations at the complete basis set limit and address the performance of different DFT methods following a specific classification based on the Jacob´s ladder in combination with various Pople's basis sets. Ab-initio calculations at the complete basis set limit are in agreement to experimental reference data and identified a significant contribution of the electron correlation energy to the bond dissociation energy (BDE) of the oxygen-oxygen bond in hydrogen peroxide and the electron affinity (EA) of the hydroxyl radical. The studied DFT methods were able to reproduce the ab-initio reference values, although no functional was particularly better for both reactions. The inclusion of HF exchange in the DFT functionals lead in most cases to larger deviations, which might be related to the poor description of the two reactions by the HF method. Considering the computational cost, DFT methods provide better BDE and EA values than HF and post--HF methods with an almost MP2 or CCSD level of accuracy. However, no systematic general prediction of the error based on the employed functional could be established and no systematic improvement with increasing the size in the Pople's basis set was found, although for BDE values certain systematic basis set dependence was observed. Moreover, the quality of the hydrogen peroxide, hydroxyl radical and hydroxyl anion structures obtained from these functionals was compared to experimental reference data. In general, bond lengths were well reproduced and the error in the angles were between one and two degrees with some systematic trend with the basis sets. From our results we conclude that DFT methods present a computationally less expensive alternative to describe the two elementary steps of the Fenton reaction. However, choice of approximated functionals and basis sets must be carefully done and the provided benchmark allows a systematic validation of the electronic structure method to be employed

scholarly journals Structural Parameters and Internal Rotational Barriers of tert-Butylammonium Ion: AM1 and ab initio Calculations

1992 ◽  
Vol 47 (12) ◽  
pp. 1255-1256
Author(s):  
Hiroyuki Ishida ◽  
Yoshihiro Kubozono ◽  
Setsuo Kashino ◽  
Ryuichi Ikeda
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Internal Rotation ◽  
Barrier Height ◽  
Structural Parameters ◽  
Mo Calculations ◽  
Ab Initio Mo Calculations ◽  
Rotational Barriers ◽  
Ab Initio Mo ◽  
Internal Rotational Barriers

Semiempirical and ab initio MO calculations were performed to estimate the structural parameters of tert-butylammonium ion and its potential energies for the internal rotation of the CH3 and NH3+ groups. The barrier height for the rotation of NH3+ was found to be lower than for that of CH3 , corresponding to the C - N bond being longer than the C - C bond.

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