Relationship between substituent-induced energy and charge effects in proton-transfer equilibria involving heteroaromatic nitrogen systems. The lone pair charge approach

1984 ◽  
Vol 106 (22) ◽  
pp. 6552-6556 ◽  
Author(s):  
J. Catalan ◽  
J. L. G. De Paz ◽  
M. Yanez ◽  
J. Elguero
Keyword(s):  
Proton Transfer ◽  
Lone Pair ◽  
Charge Effects

Density Functional Theory (DFT) and Natural Bond Orbital (NBO) Investigation of Intra/Intermolecular Hydrogen Bond Interaction in Sulfonated Nata-De Coco-Water (NDCS-(H2O)n)

2020 ◽  
Vol 17 (6) ◽  
pp. 2812-2819
Author(s):  
Sitti Rahmawati ◽  
Cynthia Linaya Radiman ◽  
Muhamad Abdulkadir Martoprawiro ◽  
Siti Nuryanti
Keyword(s):  
Hydrogen Bonds ◽  
Proton Transfer ◽  
Density Functional ◽  
Intermolecular Hydrogen Bond ◽  
Lone Pair ◽  
Dft Method ◽  
Nbo Analysis ◽  
Hydrogen Bond Interaction ◽  
Sulfonic Group ◽  
The One

This research aim to study the conformation, hydrogen bonding network, and stability of all possible molecular interactions between sulfonated nata-de-coco membranes with water (NDCS-(H2O)n), n = 1–5) as well as associate them with results of phosphorylated nata-de-coco reported previously, to determine the potential of proton transfer within both systems. The calculations used DFT method at the B3LYP/6-311G** level as well as NBO analysis. The strongest hydrogen bonds were found among sulfonic group in NDCS-(H2O)5 and the oxygen in the water molecules. The stabilization energy of NDCS-(H2O)5 is 98.9 kcal/mol, That is much greater than that found in NDCP-(H2O)5 This suggests that the NDCS was more easily to donate its lone pair and that the hydrogen bonds between sulfonic group and water molecule were stronger, so that it was easier to transfer protons to another sulfonic group than to NDCP. The energy profile showed that barrier energy was roughly 58.1 kcal/mol and 138.6 kcal/mol for NDCS-(H2O)5 and NDCP-(H2O)5 respectively. Proton transfer in NDCS-(H2O)5 generated a lower energy-barrier than the one in NDCP-(H2O)5

The relationship between substituent-induced energy and charge effects in proton-transfer equilibriums

1981 ◽  
Vol 103 (6) ◽  
pp. 1344-1349 ◽  
Author(s):  
Warren J. Hehre ◽  
Mare Taagepera ◽  
Robert W. Taft ◽  
Ronald D. Topsom
Keyword(s):  
Proton Transfer ◽  
Charge Effects ◽  
The Relationship

THE GEOMETRIES AND PROTON TRANSFER OF HYDRATED DIVALENT LEAD ION CLUSTERS [Pb(H2O)n]2+(n = 1–17)

2012 ◽  
Vol 11 (05) ◽  
pp. 1149-1164 ◽  
Author(s):  
X. L. LEI ◽  
B. C. PAN
Keyword(s):  
Proton Transfer ◽  
Experimental Observation ◽  
Density Functional ◽  
Lone Pair ◽  
Lead Ion ◽  
Functional Theory ◽  
Ion Clusters ◽  
Lone Pair Orbital ◽  
Proton Transfer Reactions ◽  
Good Agreement

The low-lying candidates of hydrated divalent lead ion clusters [ Pb(H2O) n]2+ with up to n = 17 have been extensively studied by using density functional theory (DFT) at B3LYP level. The optimized structures show that for n = 5–13 the lowest-energy structures prefer tetracoordinate with hemi-directed geometries, while the best candidates with n = 14–17 are hexacoordinate with holo-directed geometries, which is just consistent with the experimental observation. Furthermore, the origin of hemi-directed and holo-directed geometries has been revealed. It is found that in the hemi-directed geometries, the lone pair orbital has p character and fewer electrons are transferred from the water molecules to the Pb2+ ion. Contrarily, in the holo-directed geometries, the lone pair orbital has little or no p character and more electrons are transferred to the Pb2+ ion. On the other hand, the proton transfer reactions of the [ Pb(H2O) n]2+(n = 2, 4, 8) complexes have been examined, from which the predicted products of these complexes are in good agreement with the experimental observation.

A comparison of methyl and phenyl substituent effects on the gas phase basicities of amines and phosphines

1983 ◽  
Vol 61 (1) ◽  
pp. 97-102 ◽  
Author(s):  
S. Ikuta ◽  
P. Kebarle
Keyword(s):  
Proton Transfer ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Lone Pair ◽  
Phenyl Group ◽  
Ion Source ◽  
Free Base ◽  
Phenyl Substituent ◽  
Proton Affinities ◽  
Nitrogen Lone Pair

The proton affinities of phenyl phosphine and cyclohexylphosphine were measured by determining the equilibrium constants of proton transfer equilibria with a pulsed electron beam high ion source pressure mass spectrometer. These proton affinities combined with values for methyl and phenyl phosphines and the analogous amines provide an interesting comparison of the methyl and phenyl substituent effects on the basicities of phosphine and ammonia. Methyl substitution increases the basicity of both ammonia and phosphine; however, the increase is significantly larger for the phosphine. Phenyl substitution increases the basicity of ammonia and phosphine and the increase for phosphine is very much larger. Calculations at the STO-3G, 4-31G, STO-3G*, and 4-31G* (* with d orbitals) for PH3, MePH2, PhPH2, the protonated species, and the nitrogen analogues predict proton transfer reaction energies in good agreement with the experimental results. A shortening of the C—P bond is predicted for protonation of MePH2 and particularly PhPH2, while a lengthening of the C—N bond is predicted for the corresponding nitrogen compounds. The much stronger increase in proton affinity of the phosphines caused by phenyl substitution is due to the stabilization of the phenyl phosphonium ion by π donation from the phenyl group to the empty orbitals of phosphorus in the [Formula: see text] group; in contrast, in the amines, it is the free base aniline which is stabilized by conjugation of the nitrogen lone pair with the aromatic ring. This stabilization of the free base is less important in phenyl phosphine. The participating empty orbitals of phosphorus in the conjugation of phenyl with [Formula: see text] in phenyl phosphonium are mostly π* with some -πd participation. The stabilization of the aniline free base contributes considerably more than the conjugation in the phosphonium ion, to the phenyl substituent difference for the amines and phosphines. The factors involved in the bigger substituent effect of methyl in the phosphines are somewhat similar to those for phenyl: stabilization of the methyl amine by conjugation of the nitrogen lone pair with empty orbitals of CH3 and stabilization of the [Formula: see text] by hyperconjugation. An alternate description can be given in terms of hybridization changes.

scholarly journals A Combined Experimental and Computational Study of Halogen and Hydrogen Bonding in Molecular Salts of 5-Bromocytosine

Molecules ◽  
2021 ◽  
Vol 26 (11) ◽  
pp. 3111
Author(s):  
Massimiliano Aschi ◽  
Giorgia Toto Brocchi ◽  
Gustavo Portalone
Keyword(s):  
Proton Transfer ◽  
Crystal Packing ◽  
Computational Study ◽  
Theoretical Calculations ◽  
Bromine Atom ◽  
Lone Pair ◽  
Organic Salts ◽  
Dna And Rna ◽  
Molecular Salts ◽  
Derivatives Of

Although natural or artificial modified pyrimidine nucleobases represent important molecules with valuable properties as constituents of DNA and RNA, no systematic analyses of the structural aspects of bromo derivatives of cytosine have appeared so far in the literature. In view of the biochemical and pharmaceutical relevance of these compounds, six different crystals containing proton-transfer derivatives of 5-bromocytosine are prepared and analyzed in the solid-state by single crystal X-ray diffraction. All six compounds are organic salts, with proton transfer occurring to the Nimino atom of the pyridine ring. Experimental results are then complemented with Hirshfeld surface analysis to quantitively evaluate the contribution of different intermolecular interactions in the crystal packing. Furthermore, theoretical calculations, based on different arrangements of molecules extracted from the crystal structure determinations, are carried out to analyze the formation mechanism of halogen bonds (XBs) in these compounds and provide insights into the nature and strength of the observed interactions. The results show that the supramolecular architectures of the six molecular salts involve extensive classical intermolecular hydrogen bonds. However, in all but one proton-transfer adducts, weak to moderate XBs are revealed by C–Br…O short contacts between the bromine atom in the fifth position, which acts as XB donor (electron acceptor). Moreover, the lone pair electrons of the oxygen atom of adjacent pyrimidine nucleobases and/or counterions or water molecules, which acts as XB acceptor (electron donor).

Specimen Collection Effect in Scanning Electron Microscopy Images

1972 ◽  
Vol 30 ◽  
pp. 448-449
Author(s):  
J. Temple Black ◽  
Jose Guerrero
Keyword(s):  
Surface Morphology ◽  
Secondary Electron Emission ◽  
Secondary Electrons ◽  
Charge Effects ◽  
Material Density ◽  
Specimen Collection ◽  
The Subject ◽  
Curved Paths ◽  
Subject Material ◽  
Microscopy Images

In the SEM, contrast in the image is the result of variations in the volume secondary electron emission and backscatter emission which reaches the detector and serves to intensity modulate the signal for the CRT's. This emission is a function of the accelerating potential, material density, chemistry, crystallography, local charge effects, surface morphology and especially the angle of the incident electron beam with the particular surface site. Aside from the influence of object inclination, the surface morphology is the most important feature In producing contrast. “Specimen collection“ is the name given the shielding of the collector by adjacent parts of the specimen, producing much image contrast. This type of contrast can occur for both secondary and backscatter electrons even though the secondary electrons take curved paths to the detector-collector.Figure 1 demonstrates, in a unique and striking fashion, the specimen collection effect. The subject material here is Armco Iron, 99.85% purity, which was spark machined.

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