The electronic effects in and the oxygen basicity of some oxygen-containing boranes

1979 ◽  
Vol 44 (12) ◽  
pp. 3688-3694 ◽  
Author(s):  
Josef Pola ◽  
Marie Jakoubková ◽  
Václav Chvalovský
Keyword(s):  
Hydrogen Bonds ◽  
Ir Spectra ◽  
Electronic Effect ◽  
Electronic Effects ◽  
Relative Basicity ◽  
Polarizability Effect ◽  
Alkoxy Groups

The oxygen relative basicity of di-n-butylboronous anhydride ((n-C4H9)2B)2O, ethyl di-n-butylboronite (n-C4H9)2BOC2H5 and some orthoborates (RO)3B having electrondonating and electronwithdrawing groups R was measured from the IR spectra of hydrogen bonds of phenol interacting with these compounds in CCl4 and analysed by means of the Taft equation. The substituent electronic effect of (n-C4H9)2B- and (RO)2B-groups attached to the oxygen of the-OR and -OB= moieties has been estimated asa more electronwithdrawing than that of structurally alike R2Z- and (RO)2Z-groups having Z = CH and SiCH3 and is discussed in terms of the vacant 2p orbital of the boron and a weak, if any, mutual polarizability effect of the alkoxy groups in orthoborates. The trimethylsiloxy group in trimethylsilyl borate possesses reduced electronwithdrawing ability compared to that in ((CH3)3SiO)3SiCH3 as a consequence of its great polarizability.

The effects controlling the oxygen basicity in alkoxysilanes (RO)nSi(CH3)4-n. The mutual polarizability effect of alkoxy groups attached to silicon

1979 ◽  
Vol 44 (3) ◽  
pp. 750-755 ◽  
Author(s):  
Josef Pola ◽  
Marie Jakoubková ◽  
Václav Chvalovský
Keyword(s):  
Regression Analysis ◽  
Linear Regression ◽  
Electronic Effect ◽  
Linear Regression Analysis ◽  
Effect Of Substituents ◽  
Relative Basicity ◽  
Polarizability Effect ◽  
Alkoxy Groups ◽  
Individual Series

Relative basicity of the oxygen in alkoxysilanes (RO)nSi(CH3)3-n having n = 1-4 and various electrondonating and electronwithdrawing groups R measured as Δν(OH) of phenol due to its interaction with these compounds in CCl4 is shown to be chiefly controlled by the electronic effect of substituents R. Linear regression analysis of the Δν(OH) vs n relatioship for individual series (RO)nSi(CH3)4-n suggests the operation of the polarizability effect of RO groups becoming more important with increasing electronwithdrawing nature of R.

Electronic effect of and mutual polarizability in groups attached to oxygen via their C, Si, Ge, and B atoms

1982 ◽  
Vol 47 (2) ◽  
pp. 613-616 ◽  
Author(s):  
Josef Pola ◽  
Václav Chvalovský
Keyword(s):  
Electronic Effect ◽  
Relative Basicity ◽  
Polarizability Effect ◽  
Effect Parameter ◽  
Relative Acidity

Relative acidity of triphenylhydroxy substituted germane and stannane is consistent with superior electrondonating effect of (C6H5)3Ge and (C6H5)3Sn groups in these compounds. Relative basicity data of alkyl(alkoxy) boranes, methanes, silanes, and germanes (RO)nZRm (Z = B, C, Si, and Ge) are compiled. The variation of the electronic effect parameter σ of fully alkylated RmZ-groups upon substitution of their alkyl with ethoxy substituent appears for Z=B and Si to be influenced by mutual polarizability effect of ethoxy substituents. Mutual polarizability of ethoxy substituents attached to carbon and germanium is negligible.

scholarly journals Electronic effects on polypyridyl Co complex-based water reduction catalysts

RSC Advances ◽  
2021 ◽  
Vol 11 (39) ◽  
pp. 24359-24365
Author(s):  
Xusheng Guo ◽  
Chao Li ◽  
Weibo Wang ◽  
Baowen Zhang ◽  
Yuanjun Hou ◽  
...  
Keyword(s):  
Hydrogen Production ◽  
Electronic Effect ◽  
Electronic Effects ◽  
Photocatalytic Hydrogen Production ◽  
Water Reduction ◽  
Reduction Catalysts

Three isomeric Co complexes showed a significant substituent electronic effect in photocatalytic hydrogen production.

scholarly journals When Are Two Hydrogen Bonds Better than One? Accurate First-Principles Models Explain the Balance of Hydrogen Bond Donors and Acceptors Found in Proteins

2020 ◽  
Author(s):  
Vyshnavi Vennelakanti ◽  
Helena W. Qi ◽  
Rimsha Mehmood ◽  
Heather Kulik
Keyword(s):  
Hydrogen Bonds ◽  
Potential Energy Surfaces ◽  
Predictive Accuracy ◽  
Protein Structures ◽  
Geometric Constraints ◽  
Model Systems ◽  
Electronic Effects ◽  
Many Body ◽  
Wide Range ◽  
Energy Surfaces

<p>Hydrogen bonds (HBs) play an essential role in the structure and catalytic action of enzymes, but a complete understanding of HBs in proteins challenges the resolution of modern structural (i.e., X-ray diffraction) techniques and mandates computationally demanding electronic structure methods from correlated wavefunction theory for predictive accuracy. Numerous amino acid sidechains contain functional groups (i.e., hydroxyls in Ser/Thr or Tyr and amides in Asn/Gln) that can act as either HB acceptors or donors (HBA/HBD) and even form simultaneous, ambifunctional HB interactions. To understand the relative energetic benefit of each interaction, we characterize the potential energy surfaces of representative model systems with accurate coupled cluster theory calculations. To reveal the relationship of these energetics to the balance of these interactions in proteins, we curate a set of 4,000 HBs, of which > 500 are ambifunctional HBs, in high-resolution protein structures. We show that our model systems accurately predict the favored HB structural properties. Differences are apparent in HBA/HBD preference for aromatic Tyr versus aliphatic Ser/Thr hydroxyls because Tyr forms significantly stronger O–H···O HBs than N–H···O HBs in contrast to comparable strengths of the two for Ser/Thr. Despite this residue-specific distinction, all models of residue pairs indicate an energetic benefit for simultaneous HBA and HBD interactions in an ambifunctional HB. Although the stabilization is less than the additive maximum due both to geometric constraints and many-body electronic effects, a wide range of ambifunctional HB geometries are more favorable than any single HB interaction. </p>

scholarly journals Steric vs Electronic Effects: A New Look into Stability of Diastereomers, Conformers and Constitutional Isomers

2021 ◽  
Author(s):  
Sopanant Datta ◽  
Taweetham Limpanuparb
Keyword(s):  
Steric Effect ◽  
Electronic Effect ◽  
Electronic Effects ◽  
Gauche Conformation ◽  
Prevalence Data ◽  
The Stability ◽  
Stable Forms ◽  
The Right ◽  
Backbone Atoms ◽  
Meta Isomer

<div>A quantum chemical investigation of the stability of compounds with identical formulas was carried out on 23 classes of halogenated compounds made of H, F, Cl, Br, I, C, N, P, O and S atoms. The prevalence of formula in which its Z configuration, gauche conformation and meta isomer are the most stable forms is calculated and discussed. The prevalence data shows that in compounds made of carbon backbones, the electronic effect is weaker than the steric effect. The electronic factor is more important as the backbone atoms are replaced with atoms on the right and upper part of the periodic table.</div>

scholarly journals Steric vs Electronic Effects: A New Look into Stability of Diastereomers, Conformers and Constitutional Isomers

2021 ◽  
Author(s):  
Sopanant Datta ◽  
Taweetham Limpanuparb
Keyword(s):  
Steric Effect ◽  
Electronic Effect ◽  
Electronic Effects ◽  
Gauche Conformation ◽  
Prevalence Data ◽  
The Stability ◽  
Stable Forms ◽  
The Right ◽  
Backbone Atoms ◽  
Meta Isomer

<div>A quantum chemical investigation of the stability of compounds with identical formulas was carried out on 23 classes of halogenated compounds made of H, F, Cl, Br, I, C, N, P, O and S atoms. The prevalence of formula in which its Z configuration, gauche conformation and meta isomer are the most stable forms is calculated and discussed. The prevalence data shows that in compounds made of carbon backbones, the electronic effect is weaker than the steric effect. The electronic factor is more important as the backbone atoms are replaced with atoms on the right and upper part of the periodic table.</div>

Spectral manifestations of strong hydrogen bonds in seven-membered rings of pyrazolecarboxylic acid derivatives

1979 ◽  
Vol 44 (3) ◽  
pp. 781-787 ◽  
Author(s):  
Emil Svátek ◽  
Viktor Zikán ◽  
Miroslav Semonský
Keyword(s):  
Hydrogen Bonds ◽  
Ir Spectra ◽  
Frequency Shift ◽  
Bond Order ◽  
Electronic System ◽  
Uv Spectra ◽  
Carboxyl Group ◽  
Opinion Formation ◽  
Frequency Shifts ◽  
Resonance Stabilization

Strong downward frequency shifts of ν(C=O) of benzoyl or carboxyl group have been found in IR spectra of some pyrazolecarboxylic acid derivatives, and bathochromic shifts of maximum of the first band of π-π* transition have been found in their UV spectra, which can be explained by the presence of strong hydrogen bonds in seven-membered rings. Considerable frequency shift of ν(C=O) indicates lowering of order of this bond which is comparable with the bond order lowering of C=O group in six-membered conjugated chelates of the type of enolized β-diketones. In our opinion, formation of strong hydrogen bonds in seven-membered rings in pyrazolecarboxylic acids is due to the presence of the adjoining five-membered aromatic ring, which enables resonance stabilization of the whole π-electronic system in a pseudo-azulene structure.

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