scholarly journals On the Harmonic Oscillator Model of Electron Delocalization (HOMED) Index and its Application to Heteroatomic π-Electron Systems

Symmetry ◽  
2010 ◽  
Vol 2 (3) ◽  
pp. 1485-1509 ◽  
Author(s):  
Ewa D. Raczyńska ◽  
Małgorzata Hallman ◽  
Katarzyna Kolczyńska ◽  
Tomasz M. Stępniewski
Keyword(s):  
Harmonic Oscillator ◽  
Electron Delocalization ◽  
Oscillator Model ◽  
Electron Systems ◽  
Harmonic Oscillator Model

THE SUBSTITUTION EFFECT ON THE AROMATICITY OF SOME N-PHENYLACETAMIDE DERIVATIVES: A DFT STUDY

2012 ◽  
Vol 11 (06) ◽  
pp. 1331-1339 ◽  
Author(s):  
EHSAN FEREYDUNI ◽  
MAHDI KAMAEE ◽  
REZA SOLEYMANI ◽  
ROYA AHMADI
Keyword(s):  
Harmonic Oscillator ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Substitution Effect ◽  
Electron Delocalization ◽  
Oscillator Model ◽  
Hammett Constant ◽  
Functional Theory ◽  
Nucleus Independent Chemical Shift ◽  
Harmonic Oscillator Model

The relative aromaticity of some N-phenylacetamide (NPA) derivatives were investigated in which the NPA was substituted by NO2, CN, CF3, Br, Cl, F, H, CH3 , and NH2 groups at two meta and para positions. For this purpose, density functional theory calculations were applied at the B3LYP/6-31+G(d,p) level to calculate the aromaticity indices including nucleus independent chemical shift (NICS), harmonic oscillator model of aromaticity (HOMA) and harmonic oscillator model of electron delocalization (HOMED). The obtained results indicated that the aromaticity of derivatives decreased in the order of NO 2 > CN > CF 3 > Br > Cl > F > H > CH 3 > NH 2 for both meta and para positions. Furthermore, the resulting order was directly related to the electron withdrawing and electron releasing strengths of the substituents. Finally, it was found that all the aromaticity indices of have a good correlation with the Hammett constant.

scholarly journals Application of the Extended HOMED (Harmonic Oscillator Model of Aromaticity) Index to Simple and Tautomeric Five-Membered Heteroaromatic Cycles with C, N, O, P, and S Atoms

Symmetry ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 146 ◽  
Author(s):  
Ewa Raczyńska
Keyword(s):  
Harmonic Oscillator ◽  
Quantum Chemical ◽  
Chemical Method ◽  
Intramolecular Proton Transfer ◽  
Electron Delocalization ◽  
Oscillator Model ◽  
Aromaticity Index ◽  
Gibbs Energies ◽  
Structural Descriptor ◽  
Harmonic Oscillator Model

The geometry-based HOMA (Harmonic Oscillator Model of Aromaticity) descriptor, based on the reference compounds of different delocalizations of n- and π-electrons, can be applied to molecules possessing analogous bonds, e.g., only CC, only CN, only CO, etc. For compounds with different heteroatoms and a different number of CC, CX, XX, and XY bonds, its application leads to some discrepancies. For this reason, the structural descriptor was modified and the HOMED (Harmonic Oscillator Model of Electron Delocalization) index defined. In 2010, the HOMED index was parameterized for compounds with C, N and O atoms. For parametrization, the reference molecules of similar delocalizations of n- and π-electrons were employed. In this paper, the HOMED index was extended to compounds containing the CP, CS, NN, NP, PP, NO, NS, PO, and PS bonds. For geometrical optimization of all reference molecules and of all investigated heterocompounds, the same quantum–chemical method {B3LYP/6-311+G(d,p)} was used to eliminate errors of the HOMED estimation. For some tautomeric systems, the Gn methods were also employed to confirm tautomeric preferences. The extended HOMED index was applied to five-membered heterocycles, simple furan and thiophene, and their N and P derivatives as well as for tautomeric pyrrole and phosphole and their N and P derivatives. The effects of additional heteroatom(s) in the ring on the HOMED values for furan are parallel to those for thiophene. For pyrroles, aromaticity dictates the tautomeric preferences. An additional N atom in the ring only slightly affects the HOMED values for the favored and well delocalized NH tautomers. Significant changes take place for their rare CH forms. When intramolecular proton-transfer is considered for phosphole and its P derivatives, the PH tautomers seem to be favored only for 1,2,3-triphosphole/1,2,5-triphosphole and for 1,2,3,5-tetraphosphole. For other phospholes, the CH forms have smaller Gibbs energies than the PH isomers. For phosphazoles, the labile proton in the favored form is linked to the N atom. The PH forms have smaller HOMED indices than the NH tautomers but higher than the CH ones.

The harmonic oscillator model in predissociation

1978 ◽  
Vol 33 (2) ◽  
pp. 205-217 ◽  
Author(s):  
Michael L. Sink ◽  
André D. Bandrauk
Keyword(s):  
Harmonic Oscillator ◽  
Oscillator Model ◽  
Harmonic Oscillator Model
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