The Chemical Bond in Carbonyl and Sulfinyl Groups Studied by Soft X-ray Spectroscopy and ab Initio Calculations

ChemPhysChem ◽  
2012 ◽  
Vol 13 (13) ◽  
pp. 3106-3111 ◽  
Author(s):  
Kaan Atak ◽  
Nicholas Engel ◽  
Kathrin M. Lange ◽  
Ronny Golnak ◽  
Malte Gotz ◽  
...  
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Chemical Bond ◽  
X Ray

Nature of the Chemical Bond of Aqueous Fe2+ Probed by Soft X-ray Spectroscopies and ab Initio Calculations

2013 ◽  
Vol 117 (41) ◽  
pp. 12613-12618 ◽  
Author(s):  
Kaan Atak ◽  
Sergey I. Bokarev ◽  
Malte Gotz ◽  
Ronny Golnak ◽  
Kathrin M. Lange ◽  
...  
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Chemical Bond ◽  
X Ray

Ab initio calculations of X-ray emission from C60

1994 ◽  
Vol 227 (1-2) ◽  
pp. 98-102 ◽  
Author(s):  
J.-H. Guo ◽  
Y. Luo ◽  
O. Vahtras ◽  
P. Skytt ◽  
N. Wassdahl ◽  
...  
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
X Ray

ab initio MO Optimization of Molecular Structures of Fluoro- and Chloro-Substituted Dibenzo-p-dioxines and the Effect of Halogen Substitution at the 2,3,7,8-Positions on Metabolic Attack

1997 ◽  
Vol 52 (11) ◽  
pp. 1418-1431 ◽  
Author(s):  
Roland Weber ◽  
Till Kühn ◽  
Hanspaul Hagenmaier ◽  
Günter Häfelinger
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Energy Gap ◽  
Substituent Effects ◽  
Molecular Structures ◽  
X Ray ◽  
Degree Pattern ◽  
Chlorine Substituent ◽  
Homo Lumo ◽  
Good Agreement

Full ab initio optimizations were performed on the molecular structures of 24 fluorinated and chlorinated dibenzodioxines (PFDD/PCDD ) and dibenzofurans (PFDF/PCDF). Reasonable agreement was found by comparing the geometries of four calculated structures with known X-ray data from the literature. For the fluorine substituent, calculated electron densities (Mulliken total charges and π-electron charges) clearly demonstrate the opposite influence of the inductive (I) and mesomeric (M) effect. The changes in π-densities at carbons in ortho-, meta- and para-position are constant for each fluorine substituent (independent of degree, pattern, and position of substitution). It is thus possible to calculate the π-densities of the substituted dioxines by increments starting from dibenzodioxine. π-Charges from quantum mechanical calculations and the increment system show good agreement even for OctaFDD (O8FDD ), where eight substituent effects are acting additively. Compared with fluorine, the chlorine substituent exercises a smaller -I-effect and a clearly weaker +M-effect. The HOMO coefficients of the unsubstituted dibenzodioxine and dibenzofuran, extracted from ab initio calculations, yield a good explanation for the observed regioselective metabolic attack at the 2,3,7,8-positions. The squares of the HOMO-coefficients of the 2,3,7,8-positions in dibenzodioxine (DD ) are about ten times greater than those of the 1,4,6,9-positions. These HOMO coefficients are practically unaffected by halide substitution. But halogen substitution reduces strongly the electron density at the halogen-bound carbon, which, however, is a necessary prerequisite for the electrophilic oxygen transfer during metabolism. One would therefore expect halogen substitution of dibenzodioxine and dibenzofuran (DF) at the 2,3,7,8-position to hinder metabolism, as is indeed found. This provides a plausible explanation for the highly selective tissue retention of 2,3,7,8-substituted PCDDs and PCDFs. Our ab initio calculations of five tetra CDDs (T4CDDs) confirm the postulate of Kobayashi et al. [1 ] who, using semiempirical calculations, found a correlation between the toxicity of a dioxine congener and its absolute molecular hardness. The 2,3,7,8-T4CDD also exhibits the smallest absolute hardness (derived from the HOMO-LUMO energy gap) in our calculations.

X-ray Crystal Structures and ab Initio Calculations on the Photochemically Formed Dewar Isomers of the 4(3H)-Pyrimidinone Derivatives

1997 ◽  
Vol 62 (9) ◽  
pp. 2711-2719 ◽  
Author(s):  
Shun-ichi Hirokami ◽  
Akihiro Murao ◽  
Hiroko Kakuda ◽  
Hiroyuki Shinoda ◽  
Yoshinori Koga
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Crystal Structures ◽  
X Ray
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