Electrophilic Substitution in Methyl-substituted Naphthalenes III. Correlation between Experimental Results and Molecular Orbital Calculations of Reactivity Indices

1971 ◽  
Vol 49 (24) ◽  
pp. 4073-4083 ◽  
Author(s):  
P. Canonne ◽  
Le-Khac Huy ◽  
W. Forst
Keyword(s):  
Electron Density ◽  
Molecular Orbital ◽  
Predictive Value ◽  
Electrophilic Substitution ◽  
Methyl Groups ◽  
Molecular Orbital Calculations ◽  
Substrate Molecule ◽  
Simple Description ◽  
Reactivity Indices ◽  
Frontier Electron Density

Common reactivity indices (electron density qr,self-polarizability πrr, frontier electron density fr, superdelocalizability Sr, and localization energy Lr) are calculated for electrophilic substitution in 25 methyl-naphthalenes. An elementary s.c.f. method in the form of a modified ω-technique is used, using the hyperconjugative-heteroatom model for the methyl groups, with ω = 1.4, hx = 2.0, kc–x = 0.8. This choice gives reasonably good ionization potentials and very good correlation for singlet transitions (p-band) in u.v. spectra of α-methylnaphthalenes. Purely static indices qr, fr, and πrr are found to be unsuitable for predicting reactive positions for chloromethylation, while Sr and Lr are very satisfactory. On the theory that the polarizing effect of the approaching reagent is important, the index qr′ = qr + πrr δαr may be obtained, which is also found to be very satisfactory for δαr = β. If the interaction is viewed as an interaction between a hard acid (chloromethyl) and soft base (methylnaphthalenes), the index ΔEr = aqr + bfr is obtained, which is likewise found to be satisfactory with a = 1, b = 0.15. These results show clearly that it is insufficient to base reactivity considerations in methylnaphthalenes entirely on the properties of the isolated substrate molecule, but that even a very simple description of the substrate–reagent interaction is sufficient since the four indices Sr, Lr, qr′ and ΔEr all have the same predictive value.

A pairwise additivity scheme for conformational energies of substituted ethanes

1975 ◽  
Vol 343 (1632) ◽  
pp. 1-10 ◽  
Keyword(s):  
Large Deviations ◽  
Ab Initio ◽  
Dihedral Angle ◽  
Molecular Orbital ◽  
Methyl Groups ◽  
Molecular Orbital Calculations ◽  
Linear Combinations ◽  
Strongly Interacting ◽  
Conformational Energies

Ab initio molecular orbital calculations are used to explore additivity in the conformational energies of poly-substituted ethanes in terms of conformational energies of ethane and appropriate mono- and 1,2-di-substituted derivatives. Such relations would allow complex calculations for poly-substituted ethanes to be replaced by much simpler ones on a small number of parent molecules. General expressions for the linear combinations are derived from the assumption that interactions between vicinal substituents are pairwise additive and depend only on the vicinal dihedral angle. The additivity scheme is tested for 15 ethanes, di-, tri- or tetrasubstituted by cyano and methyl groups and for a smaller number of fluoroethanes. Additivity applies to within 0.1- 0.3 k J mol -1 in the methylethanes and mostly to within about 0.7- 0.8 kJ mol -1 in cyanoethanes. Large deviations are found among the geminally substituted fluoroethanes. It is suggested that the additivity approximation is most successful in the absence of strongly interacting geminal groups. Predictions are made of conformational energies of ten hexa(cyano- and methyl-) substituted ethanes.

The stabilization of alkoxide anions

1969 ◽  
Vol 47 (12) ◽  
pp. 2306-2307 ◽  
Author(s):  
N. C. Baird
Keyword(s):  
Electron Density ◽  
Molecular Orbital ◽  
Cyclotron Resonance ◽  
Molecular Orbital Calculations ◽  
Ion Cyclotron Resonance ◽  
Density Distributions ◽  
Alkyl Groups ◽  
Valence Electrons ◽  
Ion Cyclotron

Molecular orbital calculations by the MINDO method are reported for the valence electrons of HO− and a number of small alkoxide anions. The acidity order [Formula: see text] is predicted, in agreement with recent ion cyclotron resonance studies. The electron density distributions within the ions are discussed with reference to current models of the polarizability of alkyl groups.

Molecular Mimicry of Structure and Electron Density Distributions in Minerals

1986 ◽  
Vol 73 ◽  
Author(s):  
G. V. Gibbs ◽  
M. B. Boisen
Keyword(s):  
Bond Strength ◽  
Electron Density ◽  
Molecular Orbital ◽  
Computational Models ◽  
Molecular Mimicry ◽  
Strength Parameter ◽  
Molecular Orbital Calculations ◽  
Bond Lengths ◽  
Density Distributions ◽  
Reaction Energies

ABSTRACTMolecular orbital calculations on hydroxyacid molecules with first- and secondrow X-cations (X = Li through N and Na through S) yield bond lengths and angles that mimic those of chemically similar minerals. These bond lengths are used to find a formula giving bond length as a function of a bond-strength parameter that reproduces XO bond lengths in crystals with main-group X-cations from all six rows of the periodic table within 0.05Å on average. The molecular orbital calculations also provide insights into reaction energies, physical properties of crystals such as electron density distributions, and data not amenable to direct measurement. They also provide a basis from which computational models for mineral structures may be constructed.

Substitutent Effects on the Geometrical Properties of 1-Phenylallyl Alcohol

2005 ◽  
Vol 60 (4) ◽  
pp. 265-270
Author(s):  
Salim Y. Hanna ◽  
Salim M. Khalil ◽  
Moafaq Y. Shandala
Keyword(s):  
Electron Density ◽  
Molecular Orbital ◽  
Substituent Effects ◽  
Heats Of Formation ◽  
Geometrical Parameters ◽  
Molecular Orbital Calculations ◽  
Electron Densities ◽  
Geometrical Properties ◽  
Stabilization Energies

Abstract Optimized geometrical parameters, electron densities, heats of formation and stabilization energies have been obtained on X-substituted phenylallyl alcohols, where X is H, OCH3, NH2, CN, F and CH3 at ortho, meta, and para positions, using MINDO-Forces SCF-molecular orbital calculations. The substituent effects on the geometrical parameters and the electron density are discussed.

An investigation into the origins of polar substituent effects upon 19F chemical shifts, using 4-substituted β,β-difluorostyrenes

1980 ◽  
Vol 58 (8) ◽  
pp. 839-845 ◽  
Author(s):  
William F. Reynolds ◽  
Victoria G. Gibb ◽  
Nick Plavac
Keyword(s):  
Chemical Shift ◽  
Electron Density ◽  
Molecular Orbital ◽  
Excellent Agreement ◽  
Field Effect ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Molecular Orbital Calculations ◽  
Chemical Shift Difference ◽  
Polar Substituent

19F, 13C, and 1H chemical shifts have been determined for β,β-difluorostyrene and eight 4-substituted derivatives. The β-fluorine chemical shift difference, ΔδF, is used to evaluate the constant in the Buckingham equation. A = 3.0 × 10−11 esu for C—F bonds which is in excellent agreement with the value derived by Adcock and Khor. This allows accurate estimates of direct field effect contributions to 19F chemical shifts in aryl fluorides. Substituent parameter correlations demonstrate that the primary polar effect on 19F chemical shifts is field-induced π polarization. Abinitio molecular orbital calculations confirm that the substituent-induced 19F chemical shifts reflect changes in fluorine π electron density.

INDO Molecular Orbital Calculations on the Conformational Dependence of Long-range Spin–Spin Coupling of Methyl Protons in Toluene, p-Fluorotoluene, and the Xylenes

1972 ◽  
Vol 50 (12) ◽  
pp. 1852-1862 ◽  
Author(s):  
R. Wasylishen ◽  
T. Schaefer
Keyword(s):  
Molecular Orbital ◽  
Perturbation Technique ◽  
Spin Coupling ◽  
Methyl Groups ◽  
Molecular Orbital Calculations ◽  
Orbital Theory ◽  
Fluorine Nucleus ◽  
Rotational Angle ◽  
Methyl Group ◽  
Spin Spin Coupling

The conformational dependence of the nuclear spin–spin coupling from methyl protons to ring protons, to the fluorine nucleus, and to protons of other methyl groups in toluene, p-fluorotoluene, and the xylenes is computed by the finite perturbation technique in the INDO approximation of molecular orbital theory. The calculated coupling over six bonds to the proton in the para position agrees quantitatively with experiment and its predicted dependence on the rotational angle of the methyl group supports a commonly assumed π electron mechanism for the transmission of spin information between the nuclei. Similar remarks apply to the fluorine nucleus in p-fluorotoluene. The couplings over five and four bonds to the protons in the meta and ortho positions display a more complex angular dependence and the former can be interpreted in terms of a dominant σ electron mechanism. The coupling between protons in different methyl groups in the ortho and meta xylenes is calculated as rather larger than the values observed in their derivatives and in the main shows the behavior expected from a π electron mechanism. Those conformations of ortho xylene in which the coupled protons are in close proximity yield computed values plausibly attributable to "direct" and/or "through-space" mechanisms. The preferred conformation of the methyl group in toluene is predicted to have a C—H bond eclipsing the plane of the aromatic ring and the calculated barriers to rotation of 0.013 kcal/mol in toluene and of 0.014 kcal/mol in p-fluorotoluene are in quantitative accord with microwave data.

MINDO – Forces Calculation of Some Substituted Phenylallyl Cations

2004 ◽  
Vol 59 (12) ◽  
pp. 971-976
Author(s):  
Salim Y. Hanna ◽  
Salim M. Khalil ◽  
Moafaq Y. Shandala
Keyword(s):  
Correlation Analysis ◽  
Electron Density ◽  
Molecular Orbital ◽  
Geometry Optimization ◽  
Heats Of Formation ◽  
Geometrical Parameters ◽  
Molecular Orbital Calculations ◽  
Electron Densities ◽  
Stabilization Energies ◽  
Complete Geometry Optimization

MINDO-Forces SCF-molecular orbital calculations with complete geometry optimization have been performed on x-substituted phenylallyl cations, where x is H, OCH3, NH2, NO2, CN, F and CH3, in ortho, meta, or para positions. Optimized geometrical parameters, electron densities, heats of formation and stabilization energies were obtained. The substitutent effect on the geometrical parameters and the electron density are discussed by correlation analysis.

Thienoquinolines, VII. 1 Molecular Orbital Studies of Thieno(2,3-b)quinoline

1977 ◽  
Vol 32 (11) ◽  
pp. 1331-1334 ◽  
Author(s):  
Ν. Soundararajan ◽  
P. Shanmugam
Keyword(s):  
Molecular Orbital ◽  
Molecular Orbital Calculations ◽  
Atomic Charges ◽  
Cndo Method ◽  
Reactivity Indices ◽  
Internuclear Distances

The molecular orbital calculations for thieno(2,3-b)quinoline have been performed within the π-electron framework and by using the CNDO method. The calculated values for internuclear distances, atomic charges and reactivity indices for various types of reactions are presented and discussed.

Pyrazolo[1,5-a]Pyrimidine: Synthesis and Regiospecific Electrophilic Substitution in the Pyrazole and/or Pyrimidine Rings

1975 ◽  
Vol 53 (1) ◽  
pp. 119-124 ◽  
Author(s):  
Brian Maurice Lynch ◽  
Misbahul Ain Khan ◽  
Suresh Chandra Sharma ◽  
Huk Chia Teo
Keyword(s):  
Nitric Acid ◽  
Molecular Orbital ◽  
Nitro Compound ◽  
Acidic Medium ◽  
Electrophilic Substitution ◽  
Ring System ◽  
Molecular Orbital Calculations ◽  
Coupling Constant ◽  
Pyrimidine Synthesis ◽  
Conjugate Acid

A general cyclization route to pyrazolo[1,5-a]pyrimidines from 3-aminopyrazole and 1,3-dicarbonyl compounds is applied to synthesis of the parent ring system. In nitration of this species the orientation of substitution is strongly reagent dependent. Mixed nitric and sulfuric acids yield the 3-nitro compound, whereas nitric acid in acetic anhydride yields the 6-nitro compound. Brominations yield 3-bromo and 3,6-dibromo species.The majority reacting species in the strongly acidic medium is identified as the 1-protonated entity by conjoint use of approximate molecular orbital calculations and the variation of coupling constant patterns accompanying protonation. The molecular orbital calculations predict successive 3- and 6-substitution by electrophiles in pyrazolo[l,5-a]pyrimidine and its conjugate acid, and an addition–elimination sequence is proposed to account for the observed 6-nitration.

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