scholarly journals “Direct”, “Inverted” and “Superdirect” Sigma Bonds: Substituent Angles and Bond Energy. The Case of the CC Bonds in Hydrocarbons.

2020 ◽  
Author(s):  
Rubén Laplaza ◽  
Julia Contreras-García ◽  
Franck Fuster ◽  
François Volatron ◽  
Patrick Chaquin
Keyword(s):  
Dissociation Energy ◽  
Bond Energy ◽  
Multiple Bond ◽  
The Other ◽  
Hydrogen Atoms ◽  
The Mean ◽  
Sigma Bonds ◽  
Single Bonds ◽  
Sigma Bond

The A-A dissociation energy with respect to geometry frozen fragments (BE) of has been calculated for AHn-AHn models (C2H6, Si2H6, Ge2H6 and N2H4) as a function of  = H-A-A angles. Following a sigmoidal variation, BE decreases rapidly when  decreases to yield “inverted bonds” for  < 90° and finally nearly vanishes. On the contrary BE increases when  increases with respect to the equilibrium value; we propose the term of “superdirect” to qualify such bonds. This behaviour has been qualitatively interpreted in the case of C2H6 by the variation of the overlap of both s+p hybrids. The BE of one C-H bond in CH3 behaves similarly as function of its H-C-H angle with the other three hydrogen atoms. The concept of inverted/direct/superdirect bond is generalized to any CC sigma bond in hydrocarbons and can be characterized by the mean angle value <> of this bond with substituents (multiple-bonded substituents are considered as several substituents). This applies as well to formal single bonds as to sigma bonds in a formally multiple bond. <br>

scholarly journals “Direct”, “Inverted” and “Superdirect” Sigma Bonds: Substituent Angles and Bond Energy. The Case of the CC Bonds in Hydrocarbons.

2020 ◽  
Author(s):  
Rubén Laplaza ◽  
Julia Contreras-García ◽  
Franck Fuster ◽  
François Volatron ◽  
Patrick Chaquin
Keyword(s):  
Dissociation Energy ◽  
Bond Energy ◽  
Multiple Bond ◽  
The Other ◽  
Hydrogen Atoms ◽  
The Mean ◽  
Sigma Bonds ◽  
Single Bonds ◽  
Sigma Bond

The A-A dissociation energy with respect to geometry frozen fragments (BE) of has been calculated for AHn-AHn models (C2H6, Si2H6, Ge2H6 and N2H4) as a function of  = H-A-A angles. Following a sigmoidal variation, BE decreases rapidly when  decreases to yield “inverted bonds” for  < 90° and finally nearly vanishes. On the contrary BE increases when  increases with respect to the equilibrium value; we propose the term of “superdirect” to qualify such bonds. This behaviour has been qualitatively interpreted in the case of C2H6 by the variation of the overlap of both s+p hybrids. The BE of one C-H bond in CH3 behaves similarly as function of its H-C-H angle with the other three hydrogen atoms. The concept of inverted/direct/superdirect bond is generalized to any CC sigma bond in hydrocarbons and can be characterized by the mean angle value <> of this bond with substituents (multiple-bonded substituents are considered as several substituents). This applies as well to formal single bonds as to sigma bonds in a formally multiple bond. <br>

scholarly journals From “inverted” to “superdirect“ bonds: a general concept connecting substituent angles with sigma bond strengths. The case of the CC bonds in hydrocarbons.

2021 ◽  
Author(s):  
Rubén Laplaza ◽  
Julia Contreras-García ◽  
Franck Fuster ◽  
François Volatron ◽  
Patrick Chaquin
Keyword(s):  
Dissociation Energy ◽  
General Concept ◽  
Bond Energies ◽  
Multiple Bonds ◽  
Cyclic Molecules ◽  
Central Bond ◽  
Bond Strengths ◽  
The Mean ◽  
Single Bonds ◽  
Sigma Bond

<div>The C-C dissociation energy with respect to geometry frozen fragments (BE) has been calculated for C2H6 as a function of  = H-C-C angles. BE decreases rapidly when  decreases from its equilibrium value to yield the so-called “inverted bonds” for  < 90°; on the contrary BE increases</div><div>when  increases to yield somehow “superdirect” bonds, following a sigmoidal variation. The central bond in Si2H6, Ge2H6 and N 2H4 as well as the C-H bond in CH3-H behaves similarly. The concept of “invertedness”/”directedness” is generalized to any CC sigma bond in hydrocarbons and characterized by the mean angle value <> of substituents. Using dynamic orbital forces (DOF) as indices, the intrinsic  bond energies are studied as a function of <> for formally single bonds in a</div><div>panel of 22 molecules. This energy decreases from the strongest “superdirect” bonds in butadiyne, (<> = 180°) or tetrahedrylacetylene to the weakest “inverted bond” in cyclobutene, tetrahedrane, bicyclobutane and [1.1.1]propellane (<> = 60°), according to a sigmoidal variation. The <> parameter appears as a crude, but straightforward and robust, index of strain in cyclic molecules. Sigma bonds in multiple bonds of a panel of 11 molecules have most of time <> values less than 90°</div><div>and are significantly weaker than standard single bonds. Thus they can be considered as formally inverted or near inverted.</div><div><br></div>

scholarly journals Investigations of infra-red spectra. Determination of C-H frequencies (~3000 cm. -1 ) in paraffins and olefins, with some observations on “polythenes”

1940 ◽  
Vol 175 (961) ◽  
pp. 208-233 ◽  
Keyword(s):  
Double Bond ◽  
Carbon Tetrachloride ◽  
General Type ◽  
The Other ◽  
Hydrogen Atoms ◽  
Wave Numbers ◽  
Infra Red ◽  
Modes Of Vibration ◽  
Single Bonds

In a previous communication (1938) we described the results of an investigation into the infra-red absorption in the region of 3 µ of a number of hydrocarbons dissolved in carbon tetrachloride, with special reference to the absorption of ⟩CH 2 groups in different molecules. It was found that in many simple compounds the CH 2 group gave rise to two frequencies, essentially C-H valency vibrations, about 2857 and 2927 cm. -1 , and that from one compound to another these frequencies varied by only a few wave numbers. The lower frequency was identified with the mode of vibration in which the hydrogen atoms move in phase, while the other frequency was taken as the unsymmetrical mode of vibration. This assignment was substantiated by calculations with potential functions for molecules of the general type CH 2 — X , where X represents the rest of the molecule and is attached to the CH 2 group by single bonds. It was found that the CH frequencies of a CH 2 group are but little affected by the nature of X in saturated compounds, but that when the CH 2 group is attached to X by a double bond the CH frequencies are some 150 cm. -1 higher. In ethylene each CH 2 group has two CH valency modes of vibration, and since the CH 2 groups themselves can vibrate in or out of phase with one another, four CH frequency modes are possible for the C 2 H 4 molecule, two being Raman active and two infra-red active. In many molecules containing several CH 2 groups, similar coupling effects are important, and frequently four infra-red CH frequencies are observed.

scholarly journals Reduction in Hybridization: Lone Pairs Interacting with Empty p Orbitals

2020 ◽  
Author(s):  
Edmund Doerkson ◽  
Ryan Fortenberry
Keyword(s):  
Bond Energy ◽  
Alkaline Earth ◽  
Lone Pair ◽  
Alkaline Earth Metals ◽  
The Other ◽  
Bond Energies ◽  
Hydrogen Atoms ◽  
Group 14 ◽  
Atom Increase ◽  
Planar Geometries

<div> <div> <div> <p>X−NH2 and X−OH (for X = Li, BeH, BH2, Na, MgH, and AlH2) exhibit a reduction in hybridization in the N and O atoms, and likely in F, as well. CCSD(T)-F12/cc-pVTZ-F12 optimizations for all combinations of atoms smaller than chlorine (excluding the noble gasses) where the standard valences are filled with hydrogen atoms give breaks in the expected periodic trends. While most bond energies for a given atom increase when bonded to all atoms across a given row in the period table, X−NH2, X−OH, and X−F actually have the strongest bonds with X = BH2 and AlH2. Furthermore, the buildup in bond energy from the alkali to alkaline-earth metals is steady, and the decrease to Group 14 and beyond is also steady. The interactions of X−NH2 and X−OH with X = Li, BeH, BH2, Na, MgH, and AlH2 also produce either linear or fully planar geometries. All of these factors imply that the lone pair on the N or O atoms are datively bonding with the empty <i>p</i> orbitals in the other atoms. This leads to a reduction in hybridization. The non-periodic strengths of these bonds have implications for the detection of molecules in space as well as in models for the formation of refractory molecules and condensation of mineral species in early stages of planet formation. </p> </div> </div> </div>

Dissociation of the phenanthroimidazole dimer — A highly delocalized radical — Gomberg revisited

2005 ◽  
Vol 83 (9) ◽  
pp. 1448-1459 ◽  
Author(s):  
Eric Kiepek ◽  
Yuhui Zhou ◽  
Shmaryahu Hoz ◽  
Ester Rozental ◽  
Peter M Kazmaier ◽  
...  
Keyword(s):  
Spin Density ◽  
Bond Dissociation Energy ◽  
Dissociation Energy ◽  
Bond Energy ◽  
Structure Study ◽  
The Other ◽  
X Ray ◽  
Bond Dissociation ◽  
Order Of Magnitude ◽  
Experimental Structure

Results of a calculational study at the B3LYP/6-3/G* level concerning the dimerization of the phenanthroimidazole radical are reported herein. The optimized minimum energies of six dimer structures corresponding to C—C, C—N, and N—N bonding have been obtained. The lowest energy dimer is found to be that resulting from N—N bonding (12). However, this does not correspond to an X-ray structure study of the experimentally isolated dimer (13), which reveals C—N bonding, as is also deduced from an NMR investigation. The variance between the experimental structure and the calculational lowest energy one is examined on the basis of steric interactions: virtually retained planarity, and hence, full conjugation in the two phenanthroimidazole halves in 12, vs. twisting and lack of coplanarity in the other dimer structures. Importantly, spin density calculations reveal a negligible spin density on the nitrogens, rendering dimer 12 formation through N—N bonding highly improbable. A bond dissociation energy of 16.5 kcal/mol (1 cal = 4.184 J) is calculated for the experimental dimer 13, which is by far the lowest C—N bond energy recorded so far in the literature. As well, this value is of the same order of magnitude as the calculated C—C BDE in hexaphenylethane, which had been postulated by Gomberg in 1900 as the molecule formed on dimerization of the triphenymethyl radical, but so far not observed experimentally. Key words: delocalized radical dimerization, phenanthroimidazole dimer, Gomberg's dimer, X-ray structure, C—N bond dissociation energy.

scholarly journals Reduction in Hybridization: Lone Pairs Interacting with Empty p Orbitals

2020 ◽  
Author(s):  
Edmund Doerkson ◽  
Ryan Fortenberry
Keyword(s):  
Bond Energy ◽  
Alkaline Earth ◽  
Lone Pair ◽  
Alkaline Earth Metals ◽  
The Other ◽  
Bond Energies ◽  
Hydrogen Atoms ◽  
Group 14 ◽  
Atom Increase ◽  
Planar Geometries

<div> <div> <div> <p>X−NH2 and X−OH (for X = Li, BeH, BH2, Na, MgH, and AlH2) exhibit a reduction in hybridization in the N and O atoms, and likely in F, as well. CCSD(T)-F12/cc-pVTZ-F12 optimizations for all combinations of atoms smaller than chlorine (excluding the noble gasses) where the standard valences are filled with hydrogen atoms give breaks in the expected periodic trends. While most bond energies for a given atom increase when bonded to all atoms across a given row in the period table, X−NH2, X−OH, and X−F actually have the strongest bonds with X = BH2 and AlH2. Furthermore, the buildup in bond energy from the alkali to alkaline-earth metals is steady, and the decrease to Group 14 and beyond is also steady. The interactions of X−NH2 and X−OH with X = Li, BeH, BH2, Na, MgH, and AlH2 also produce either linear or fully planar geometries. All of these factors imply that the lone pair on the N or O atoms are datively bonding with the empty <i>p</i> orbitals in the other atoms. This leads to a reduction in hybridization. The non-periodic strengths of these bonds have implications for the detection of molecules in space as well as in models for the formation of refractory molecules and condensation of mineral species in early stages of planet formation. </p> </div> </div> </div>

Multi-Center Study of Thromboplastin Calibration Precision – Influence of Reagent Species, Composition, and International Sensitivity Index (ISI)

1993 ◽  
Vol 69 (01) ◽  
pp. 035-040 ◽  
Author(s):  
A M H P van den Besselaar ◽  
R M Bertina
Keyword(s):  
Oral Anticoagulants ◽  
International Normalized Ratio ◽  
The Other ◽  
World Health ◽  
Rabbit Brain ◽  
Sensitivity Index ◽  
Bovine Plasma ◽  
Significant Difference ◽  
The Mean ◽  
International Sensitivity Index

SummaryFour thromboplastin reagents were tested by 18 laboratories in Europe, North-America, and Australasia, according to a detailed protocol. One thromboplastin was the International Reference Preparation for ox brain thromboplastin combined with adsorbed bovine plasma (coded OBT/79), and the second was a certified reference material for rabbit brain thromboplastin, plain (coded CRM 149R). The other two thromboplastin reagents were another rabbit plain brain thromboplastin (RP) with a lower ISI than CRM 149R and a rabbit brain thromboplastin combined with adsorbed bovine plasma (RC). Calibration of the latter two reagents was performed according to methods recommended by the World Health Organization (W. H. O.).The purpose of this study was to answer the following questions: 1) Is the calibration of the RC reagent more precise against the bovine/combined (OBT/79) than against the rabbit/plain reagent (CRM 149R)? 2) Is the precision of calibration influenced by the magnitude of the International Sensitivity Index (ISI)?The lowest inter-laboratory variation of ISI was observed in the calibration of the rabbit/plain reagent (RP) against the other rabbit/plain reagent (CRM 149R) (CV 1.6%). The highest interlaboratory variation was obtained in the calibration of rabbit/plain (RP) against bovine/combined (OBT/79) (CV 5.1%). In the calibration of the rabbit/combined (RC) reagent, there was no difference in precision between OBT/79 (CV 4.3%) and CRM 149R (CV 4.2%). Furthermore, there was no significant difference in the precision of the ISI of RC obtained with CRM 149R (ISI = 1.343) and the rabbit/plain (RP) reagent with ISI = 1.14. In conclusion, the calibration of RC could be performed with similar precision with either OBT/79 or CRM 149R, or RP.The mean ISI values calculated with OBT/79 and CRM 149R were practically identical, indicating that there is no bias in the ISI of these reference preparations and that these reference preparations have been stable since their original calibration studies in 1979 and 1987, respectively.International Normalized Ratio (INR) equivalents were calculated for a lyophilized control plasma derived from patients treated with oral anticoagulants. There were small but significant differences in the mean INR equivalents between the bovine and rabbit thromboplastins. There were no differences in the interlaboratory variation of the INR equivalents, when the four thromboplastins were compared.

Prothrombin Time Standardization: Report of the Expert Panel on Oral Anticoagulant Control

1979 ◽  
Vol 42 (04) ◽  
pp. 1073-1114 ◽  
Keyword(s):  
Prothrombin Time ◽  
Expert Panel ◽  
The Other ◽  
Rabbit Brain ◽  
Calibration Constant ◽  
Freeze Dried ◽  
The Mean ◽  
Point Of Intersection ◽  
And Control ◽  
Standardization Report

SummaryIn collaborative experiments in 199 laboratories, nine commercial thromboplastins, four thromboplastins held by the National Institute for Biological Standards and Control (NIBS & C), London and the British Comparative Thromboplastin were tested on fresh normal and coumarin plasmas, and on three series of freeze-dried plasmas. One of these was made from coumarin plasmas and the other two were prepared from normal plasmas; in each series, one plasma was normal and the other two represented different degrees of coumarin defect.Each thromboplastin was calibrated against NIBS&C rabbit brain 70/178, from the slope of the line joining the origin to the point of intersection of the mean ratios of coumarin/normal prothrombin times when the ratios obtained with the two thromboplastins on the same fresh plasmas were plotted against each other. From previous evidence, the slopes were calculated which would have been obtained against the NIBS&C “research standard” thromboplastin 67/40, and termed the “calibration constant” of each thromboplastin. Values obtained from the freeze-dried coumarin plasmas gave generally similar results to those from fresh plasmas for all thromboplastins, whereas values from the artificial plasmas agreed with those from fresh plasmas only when similar thromboplastins were being compared.Taking into account the slopes of the calibration lines and the variation between laboratories, precision in obtaining a patient’s prothrombin time was similar for all thromboplastins.

Platelet Suruival and Function in Rats with Enhanced Thrombotic Tendency

1985 ◽  
Vol 54 (04) ◽  
pp. 739-743 ◽  
Author(s):  
Federica Delaini ◽  
Elisabetta Dejana ◽  
Ine Reyers ◽  
Elisa Vicenzi ◽  
Germana De Bellis Vitti ◽  
...  
Keyword(s):  
Arachidonic Acid ◽  
Nephrotic Syndrome ◽  
Platelet Function ◽  
Laboratory Tests ◽  
Thrombus Formation ◽  
The Other ◽  
Mean Survival Time ◽  
The Mean ◽  
And Function ◽  
Thrombotic Tendency

SummaryWe have investigated the relevance of some laboratory tests of platelet function in predicting conditions of thrombotic tendency. For this purpose, we studied platelet survival, platelet aggregation in response to different stimuli, TxB2 and 6-keto-PGFlα production in serum of rats bearing a nephrotic syndrome induced by adriamycin. These animals show a heavy predisposition to the development of both arterial and venous thrombosis. The mean survival time was normal in nephrotic rats in comparison to controls. As to aggregation tests, a lower aggregating response was found in ADR-treated rats using ADP or collagen as stimulating agents. With arachidonic acid (AA) we observed similar aggregating responses at lower A A concentrations, whereas at higher AA concentrations a significantly lower response was found in nephrotic rats, despite their higher TxB2 production. Also TxB2 and 6-keto-PGFlα levels in serum of nephrotic rats were significantly higher than in controls. No consistent differences were found in PGI2-activity generated by vessels of control or nephrotic rats.These data show that platelet function may appear normal or even impaired in rats with a markedly increased thrombotic tendency. On the other hand, the significance of high TxB2 levels in connection with mechanisms leading to thrombus formation remains a controversial issue.

Voronoi Analysis of a Soccer Game

2004 ◽  
Vol 9 (3) ◽  
pp. 233-240 ◽  
Author(s):  
S. Kim
Keyword(s):  
Collective Behavior ◽  
Quantitative Assessment ◽  
The Other ◽  
Analysis Method ◽  
Random System ◽  
Soccer Game ◽  
Voronoi Polygons ◽  
The Mean

This paper describes a Voronoi analysis method to analyze a soccer game. It is important for us to know the quantitative assessment of contribution done by a player or a team in the game as an individual or collective behavior. The mean numbers of vertices are reported to be 5–6, which is a little less than those of a perfect random system. Voronoi polygons areas can be used in evaluating the dominance of a team over the other. By introducing an excess Voronoi area, we can draw some fruitful results to appraise a player or a team rather quantitatively.

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