scholarly journals Rotational Barrier and Conjugation: Theoretical Study of Resonance Stabilization of Various Substituents for the Donors NH2 and OCH3 in Substituted 1,3-Butadienes

2019 ◽  
Vol 19 (4) ◽  
pp. 1055
Author(s):  
Ali Hussain Yateem
Keyword(s):  
Density Functional ◽  
Theoretical Study ◽  
Amino Nitrogen ◽  
Conjugated Systems ◽  
Rotational Barriers ◽  
Out Of Plane ◽  
Resonance Stabilization ◽  
The Difference ◽  
Internal Rotational Barriers ◽  
Single Bonds

The barrier to internal rotation around the central C2–C3 single bond of a series of (1E)-monosubstituted 1,3-butadienes and (1E,3E)-1-Y-4-X-disubstituted butadienes, with Y=NH2 or OCH3 and X=NO2, CHO, COOH, CN, CF3, Cl or F, were studied at the density functional w B97X-D/6-31G∗∗ level. The effect of substituents on π-conjugation in disubstituted 1,3-butadienes was studied by correlating the calculated internal rotational barriers with the difference in structural, atomic and molecular properties between the transition state TS and the s-trans conformers. The calculated differences in lengths of C–C, C–NH2 and C–OCH3 single bonds, N-H-N, and C-O-CH3 angles, NH2 out-of-plane angle, natural charges on amino nitrogen and methoxy oxygen, and the maximum electrostatic potential on amino hydrogens, were found to correlate strongly with the rotational barriers. The conjugative interaction was strongly stabilized in the case of strong π-electron acceptors such as NO2 or CHO and is slightly or negligibly affected with Cl and F groups. The resonance stabilization with the remaining acceptors decreases in the order COOH > CN > CF3. Acceptors X maintain their relative order of stabilization for the two donors, and NH2 is more stabilizing. Dominant resonance structures are suggested for highly and negligibly conjugated systems.

scholarly journals Rotational barrier and electron-withdrawing substituent effects: Theoretical study of -conjugation in para-substituted anilines

2020 ◽  
Vol 10 (4) ◽  
pp. 319-334
Author(s):  
Ali Hussain Yateem
Keyword(s):  
Density Functional ◽  
Amino Nitrogen ◽  
Substituent Effects ◽  
Lone Pair ◽  
Rotational Barrier ◽  
Substituted Anilines ◽  
Mechanical Approach ◽  
Resonance Stabilization ◽  
Quantum Mechanical Approach ◽  
Electron Withdrawing Substituents

The rotational barrier RB around C–NH2 bond between the minimum and maximum states of 84 electron-withdrawing groups at para-position in aniline were studied at the density functional wB97X-D/6-31G** level. The rotational barrier was found to correlate strongly with shortening of the C–NH2 bond, increase of flattening of NH2 group, decrease in negative natural charge on amino nitrogen, increase in minimum ionization potential around lone pair of amino nitrogen, increase in maximum (positive) electrostatic potential on amino hydrogens, increase in NH2 stretching frequencies, and increase in stabilization energy. The rotational barrier was also found to correlate well with empirical pKa and Hammett σp constants. The rotational barrier is shown to be a reliable quantum mechanical approach to measure p-conjugation in para-substituted anilines.  Based on RB a quantitative scale is constructed for the ability of electron-withdrawing substituents to resonate with aniline. A quinone-like structure has been proposed for stronger electron-withdrawing substituents where an extension of resonance stabilization requires the simultaneous presence of electron donor (NH2) and electron-withdrawing groups.

scholarly journals Theoretical Study on the Difference in Electron Conductivity of a One-Dimensional Penta-Nickel(II) Complex between Anti-Ferromagnetic and Ferromagnetic States—Possibility of Molecular Switch with Open-Shell Molecules

Molecules ◽  
2019 ◽  
Vol 24 (10) ◽  
pp. 1956
Author(s):  
Yasutaka Kitagawa ◽  
Hayato Tada ◽  
Iori Era ◽  
Takuya Fujii ◽  
Kazuki Ikenaga ◽  
...  
Keyword(s):  
Density Functional ◽  
Theoretical Study ◽  
Open Shell ◽  
Molecular Switch ◽  
Electron Conductivity ◽  
Molecular Wire ◽  
Functional Theory ◽  
One Dimensional ◽  
Atom Chain ◽  
The Difference

The electron conductivity of an extended metal atom chain (EMAC) that consisted of penta-nickel(II) ions bridged by oligo-α-pyridylamino ligands was examined by density functional theory (DFT) and elastic scattering Green’s functions (ESGF) calculations. The calculated results revealed that an intramolecular ferromagnetic (FM) coupling state showed a higher conductivity in comparison with an anti-ferromagnetic (AFM) coupling state. The present results suggest the potential of the complex as a molecular switch as well as a molecular wire.

Theoretical study of substituent effects on the geometry and strain enthalpy in [2,2]paracyclophanes

2016 ◽  
Vol 9 (1) ◽  
pp. 6-13 ◽  
Author(s):  
Martin Michalík ◽  
Peter Poliak ◽  
Vladimír Lukeš
Keyword(s):  
Gas Phase ◽  
Density Functional ◽  
Theoretical Study ◽  
Substituent Effects ◽  
Functional Theory ◽  
Out Of Plane ◽  
Phenyl Rings ◽  
Strain Enthalpy ◽  
Substituent Constants ◽  
Repulsive Forces

Abstract The substituent effect on the geometry and strain enthalpy of [2,2]paracyclophane is theoretically investigated by density functional theory. Gas-phase calculations were performed for twenty distinct electron donating and electron withdrawing substituents. The largest out-of-plane distortion of phenyl rings is exhibited by —SCN and —CF3 groups. On the other hand, —OH, —CH3 and —F groups show the minimal deformation. The strain enthalpy for unsubstituted [2,2]paracyclophane associated with repulsive forces between phenyl units reached up to 118.5 kJ mol−1. Any substitution causes increase of the strain enthalpy value proportionally to the absolute values of Hammett para-substituent constants. Two separate linear dependences with similar slopes were obtained for monosubstituted as well as double symmetrically substituted derivatives.

Theoretical study of the internal rotational barriers of fluorine, chlorine, bromine, and iodine-substituted ethanes

2019 ◽  
Vol 1166 ◽  
pp. 112589
Author(s):  
Sílvio Quintino de Aguiar Filho ◽  
Adão Marcos Ferreira Costa ◽  
Igor Hernandes Santos Ribeiro ◽  
Rogério Custodio ◽  
Douglas Henrique Pereira
Keyword(s):  
Theoretical Study ◽  
Rotational Barriers ◽  
Internal Rotational Barriers

scholarly journals Theoretical study of internal rotational barriers of electrons donating and electrons withdrawing groups in aromatic compounds

Heliyon ◽  
2020 ◽  
Vol 6 (9) ◽  
pp. e04957
Author(s):  
Daniel Rodrigues Lima ◽  
Sílvio Quintino de Aguiar Filho ◽  
Laura Beatriz Camargo do Oh ◽  
Anna Karla dos Santos Pereira ◽  
Douglas Henrique Pereira
Keyword(s):  
Aromatic Compounds ◽  
Theoretical Study ◽  
Rotational Barriers ◽  
Internal Rotational Barriers
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