Molecular-orbital calculations on electrophilic substitution and relative basicities in pyrrole, indole, furan, and benzofuran

1968 ◽  
Vol 2 (1) ◽  
pp. 165-177 ◽  
Author(s):  
Robert B. Hermann
Keyword(s):  
Molecular Orbital ◽  
Electrophilic Substitution ◽  
Molecular Orbital Calculations

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.

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.

Interactions between Methylene Blue and Pullulan According to Molecular Orbital Calculations

2020 ◽  
Vol 140 (11) ◽  
pp. 529-533
Author(s):  
Pasika Temeepresertkij ◽  
Saranya Yenchit ◽  
Michio Iwaoka ◽  
Satoru Iwamori
Keyword(s):  
Methylene Blue ◽  
Molecular Orbital ◽  
Molecular Orbital Calculations

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.

ChemInform Abstract: MOLECULAR ORBITAL CALCULATIONS ON THE C2H4SH+ CATION

1976 ◽  
Vol 7 (10) ◽  
pp. no-no
Author(s):  
JAMES W. GORDON ◽  
GEORGE H. SCHMID ◽  
IMRE G. CSIZMADIA
Keyword(s):  
Molecular Orbital ◽  
Molecular Orbital Calculations
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