Steric effects and steric inhibition of resonance: structure and ionization of 2-tert-butylbenzoic acid

We report detailed Density Functional Theory (DFT) investigations of a series of structurally similar titanium (IV) chelating σ-aryl catalysts. Particular attention was paid to the electronic charges of the Ti, C ipso of the substituted aryl group and the benzylic CH2 and Cipso atoms. The Bader and NBO derived charges were compared with the recently reported polymerisation results by Chan. We found a strong correlation between the relative energies of one of the computed isomers and the activity of the catalyst. Neither NBO nor Bader charges could be convincingly correlated to the observed activity.

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Estimate of Hyperconjugation Strength in Alkylaromatics and Unsaturated Hydrocarbons Derived from Refractometric Data

Current Organic Chemistry ◽

10.2174/1385272823666191108100747 ◽

2020 ◽

Vol 23 (23) ◽

pp. 2598-2613

Author(s):

Boris A. Zaitsev

Keyword(s):

Quantitative Estimation ◽

Physical Phenomenon ◽

Unsaturated Hydrocarbons ◽

Resonance Effects ◽

Alkyl Derivatives ◽

Retrospective View ◽

Scientific Papers ◽

Polycyclic Aromatic ◽

Qualitative Measure ◽

Steric Inhibition Of Resonance

: A retrospective view of exaltation of refraction observed for many unsaturated and aromatic compounds demonstrates that this physical phenomenon is undeservedly considered only as a qualitative measure of conjugation. This mini-review discusses numerous papers by the author that have been published earlier in inaccessible periodicals and collections of scientific papers. Using a great number of illustrations, the author shows that this parameter can be successfully used for quantitative estimate of resonance effects in organic and polymer chemistry. The methods for derivation of strictly additive atomic and group refraction constants are described; these constants were subsequently used as a tool that allowed quantitative estimation of resonance effects in mono-, di-, tri- and polyalkylbenzenes, alkylnaphthalenes, some alkyl derivatives of unsaturated hydrocarbons. These effects cause strictly fixed increase in refraction of carbon atoms in different structural modifications (graphene, fullerene, diamond) and in polycyclic aromatic hydrocarbons. The relevant results regarding quantitative estimation of degree of steric inhibition of resonance in sterically hindered ortho-dialkylbenzenes, 1,2,3- trialkyl-, 1,2,3,4-tetraalkyl-, and 1,2,3,4,5-polyalkylbenzenes accumulated by the author are summarized.

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Configuration on the C=N double bond of monosubstituted amidines and amidoximes

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19893245 ◽

1989 ◽

Vol 54 (12) ◽

pp. 3245-3252 ◽

Cited By ~ 13

Author(s):

Bernard Tinant ◽

Janine Dupont-Fenfau ◽

Jean-Paul Declercq ◽

Jaroslav Podlaha ◽

Otto Exner

Keyword(s):

Double Bond ◽

Nitrogen Atom ◽

Steric Effects ◽

Model Compounds ◽

X Ray ◽

Analogous Model

Configuration on the C=N double bond of amidines and amidoximes is controlled by steric effects on the second nitrogen atom but there is a difference in the case of N’-monosubstituted derivatives: amidines prefer E configuration (conformation around the C-N bond sp) and amidoximes Z configuration (conformation ap). This was confirmed by the X-ray structures of two analogous model compounds N,N’-dimethyl-4-nitrobenzamidine (monoclinic, P21c, a = 10.855(3), b = 11.043(3), c = 8.593(3) Å, β = 105.69(2)°, V = 991.8(5) Å3, Z = 4, Dx = 1.29 g cm-3, CuKα, λ = 1.5418 Å, μ = 7.91 cm-1, F(000) = 408, T = 291 K, R = 0.065 for 1 265 observed reflections) and N’-methyl-4-nitrobenzamidoxime (monoclinic, P21/a, a = 6.699(2), b = 24.178(9), c = 6.075(2) Å, β = 106.20(3)°, V = 944.9(6) Å3, Z = 4, Dx = 1.37 g cm-3, CuKα, λ = 1.5418 Å, μ =9.22 cm-1, F(000) = 408, T = 291 K, R = 0.079 for 1 278 observed reflections).

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