Heats of mixing of trialkylamines: disorder and steric hindrance contributions

1978 ◽  
Vol 56 (22) ◽  
pp. 2856-2865 ◽  
Author(s):  
Robert Philippe ◽  
Geneviève Delmas ◽  
Phuong Nguyen Hong
Keyword(s):  
Steric Hindrance ◽  
Significant Contribution ◽  
Orientational Order ◽  
Class A ◽  
Heats Of Mixing ◽  
Class B ◽  
Chain Compounds ◽  
Sterically Hindered ◽  
Long Chain ◽  
Long Chains

Nine trialkylamines, triethyl- to trihexylamine trioctyl-, tridodecyl, tri(methyl-2-butyl)-, and dimethyldodecylamine have been used for heats of mixing of the following systems at 298 K: A, fourteen systems made of all the possible binary mixtures (except one) of the six shorter amines; B, twelve systems made of a long chain amine, trioctyl-, tridodecyl- or dimethyldodecylamine with the four shorter members of the series; C, two systems consisting of the mixture of two long-chain compounds, trioctylamine with tridodecyl- and dimethyldodecylamine. Heats for the class A systems are less than or equal to 40 J/mol, indicating no net effect of the small polarity of the shorter members of the series. The experimental HE of these mixtures are compared with two theories. The Monte Carlo approach gives good predictions but the heats calculated with the Snider–Herrington theory are too negative. Heats of the class B systems are suitable for the investigation of two new contributions to the heats of mixing, the positive heat of disordering of long-chains HE(dis.) and the negative heat found in systems where one of the components is sterically hindered, HE(ster.hindr.). HE(dis.) found with the long-chain amines indicates an orientational order larger than in the case of the n-alkane of the same chain-length but equivalent to that found in the tetraalkyltin compounds of the same length. Recent work has shown that the tetrapropyl and tetraethyltin derivatives when mixed with long-chain alkanes or tin derivatives give rise to a HE(ster.hindr.) contribution. From this work and the present study, the steric hindrance contributions of five sterically hindered compounds tetraethyltin and tetrapropyltin, triethyl- and tripropylamine, and 3,3-diethylpentane mixed with different second components are calculated. The steric hindrance contribution is found proportional to the volume of the second component and increasing in the following order of the sterically hindered component: triethyl- < tripropylamine < tetraethyl- < tetrapropyltin < 3,3-diethylpentane. Heats of the class C systems are small without significant contribution of HE(dis.) due to the fitting of the long-chains in solution.

Excess heat capacities and excess volumes of tetraalkyltin compounds: . Effect of correlations of molecular orientations and steric hindrance. Part 1

1984 ◽  
Vol 62 (6) ◽  
pp. 1008-1015 ◽  
Author(s):  
Bernard Riedl ◽  
Geneviève Delmas
Keyword(s):  
Steric Hindrance ◽  
Central Atom ◽  
Orientational Order ◽  
Excess Volumes ◽  
Pure Liquid ◽  
Flory Theory ◽  
Flow Calorimeter ◽  
Alkyl Chains ◽  
Chain Compounds ◽  
Long Chain

A Picker flow calorimeter has been used to obtain molar excess capacities [Formula: see text] through the concentration range at 25 °C for the systems [Formula: see text] where R is the alkyl group CnH2n+1, (n = 1, 2, 3, 4, 8, 12). Excess volumes have also been measured for the mixtures. Two contributions to [Formula: see text] and vE were investigated: those associated with disordering the long alkyl chains and with steric hindrance. The steric hindrance contribution has been found to occur for molecules having a highly substituted central atom. The sign of this contribution is negative in hE and positive in [Formula: see text], indicative of an ordering or loss of mobility for the molecules going from pure liquid to solution. The [Formula: see text] results confirm the more sterically hindered character of the ethyl and propyl derivatives already found with hE. The separation of the disorder and steric contribution is possible in systems involving long-chain compounds. It is found that the orientational order contribution diminishes more slowly with temperature than the steric hindrance effect. The trend of vE in the series is reasonably well predicted by the Prigogine–Patterson–Flory theory.

Heats and free energies of mixing of tridodecylamine with nine heptane isomers, two octanes, and one hexane. Disorder and steric hindrance contributions

1978 ◽  
Vol 56 (18) ◽  
pp. 2472-2479 ◽  
Author(s):  
Michèle Couchon ◽  
Phuong Nguyen Hong ◽  
Genevieve Delmas
Keyword(s):  
Steric Hindrance ◽  
Free Energies ◽  
Negative Contribution ◽  
Flory Theory ◽  
Class A ◽  
Heats Of Mixing ◽  
Linear Alkanes ◽  
Class B ◽  
Class C ◽  
Branched Isomer

Heats and free energies of mixing have been measured at 298 K for tridodecylamine in n-C7, and eight branched isomers, n-C8 and one branched isomer, and a branched hexane. Heats of mixing are such that these systems can be divided in three classes. Class A [Formula: see text] includes n-C7, and n-C8. Class B [Formula: see text] includes isomers which do not have two substituents on neighbouring carbon atoms, i.e. 2-MeC6 2,2-diMeC5, 2,4-diMeC5, 2,2,4-triMeC5. Class C which includes isomers having substituents on neighbouring carbon atoms; 2,3-diMeC5, 2,2,3-triMeC4, 3-MeC6, 3,3-diMeC5, 3-EtC5, has smaller values of heats of mixing [Formula: see text]. These results are interpreted as not showing an extensive destruction of the correlations of orientations of the dodecyl chains by the linear alkanes of class A. The larger heats of class B are indicative of more disorientations of the long chains by the globular isomers. The smaller values of the heats for class C are seen as the balance of a positive disordering contribution and a negative one. The negative contribution is associated with a sterically hindered character of the compounds having substituents on neighbouring atoms. Free energies of mixing do not separate in the same three classes. This is thought to be due to an enthalpy–entropy compensation in the disordering and steric hindrance contributions. The Xl2S1−l parameter of the Flory theory shows the same variation as HE.

Excess heats of tri-n-alkylamines and tetraalkyl tin compounds in linear and branched alkanes: correlations of molecular orientations and steric hindrance effect

1979 ◽  
Vol 57 (5) ◽  
pp. 517-525 ◽  
Author(s):  
R. Philippe ◽  
G. Delmas ◽  
Phuong Nguyen Hong
Keyword(s):  
Steric Hindrance ◽  
Solution Structure ◽  
The Other ◽  
Short Chain ◽  
Flory Theory ◽  
Tin Compounds ◽  
Branched Alkanes ◽  
Linear Alkanes ◽  
Chain Compounds ◽  
Long Chain

Excess heats of the following mixtures of trialkylamines and tetraalkyl tin compounds with branched and linear alkanes have been measured at 25 °C: five trialkylamines NR3 (R = C2H5, C3H7, C4H9, C10H21, C12H25) with six linear alkanes, n-C5, n-C6, n-C8, n-C10, n-C12, n-C16, and three highly branched alkanes, 2,2,4-trimethylpentane, 2,2,4,6,6-pentamethylheptane, and 2,2,4,4,6,8,8-heptamethylnonane (br-C16). Further measurements were carried out on tetrapropyl tin (SnPr4) with n-C8, n-C16, and br-C16.Measurements were made to obtain more information on the heats of disordering of long chain compounds and on an exothermic contribution to the heats coming possibly from the sterically hindered character of one of the components of the mixture. The three short-chain trialkylamines have large heats with the linear long alkanes and small heats with the branched alkanes. On the other hand, the two long-chain trialkylamines have very small heats with linear alkanes and large heats with the branched alkanes. These results are interpreted as indicating no change of liquid or solution 'structure' when two ordered compounds (long alkanes and long-chain amines) are mixed but a change of 'structure' when an ordered compound (long alkane or long-chain amine) is mixed with a non-ordered one (branched alkane or short-chain amine). The heat of disordering of n-hexadecane is obtained with many order breakers and found to depend to some extent on the expansion coefficient of the order breaker. HE values for the series of the shorter NR3 do not vary regularly with molecular weight but are smaller for the propyl (and possibly the ethyl) derivative. Similarly, HE of SnPr4 in n-C16, br-C16, and n-C8 are much lower than the corresponding heats with SnEt4 and SnBut4. This is attributed to the presence of the exothermic contribution to the heats, HE(steric hindrance). The X12 parameter of the Flory theory has been calculated and is interpreted in terms of the disorder and steric hindrance contributions to the heats.

Synthesis of Conjugated Triynes via Alkyne Metathesis

2019 ◽  
Author(s):  
Idriss Curbet ◽  
Sophie Colombel-Rouen ◽  
Romane Manguin ◽  
Anthony Clermont ◽  
Alexandre Quelhas ◽  
...  
Keyword(s):  
Steric Hindrance ◽  
High Selectivity ◽  
Alkyne Metathesis ◽  
Cross Metathesis ◽  
Synthetic Strategy ◽  
Sterically Hindered ◽  
Site Selective

<div> <div> <div> <div> <p>The synthesis of conjugated triynes by molybdenum-catalyzed alkyne metathesis is reported. Strategic to the success of this approach is the utilization of sterically-hindered diynes that allowed for the site- selective alkyne metathesis to produce the desired con- jugated triyne products. The steric hindrance of alkyne moiety was found to be crucial in preventing the for- mation of diyne byproducts. This novel synthetic strategy was amenable to self- and cross-metathesis providing straightforward access to the corresponding symmetrical and dissymmetrical triynes with high selectivity. </p> </div> </div> </div> </div>

مهارة الكلام منظور من عملية التعلم والتعليم في جامعة باتوسنجكر الاسلامية الحكومية سومطرى الغربية

2019 ◽  
Vol 1 (1) ◽  
Author(s):  
Suharmon Suharmon
Keyword(s):  
Teaching Strategies ◽  
Language Education ◽  
Arabic Language ◽  
Descriptive Statistics ◽  
Quantitative Approach ◽  
Motivation To Learn ◽  
Education Department ◽  
Class A ◽  
Class B ◽  
Speaking Skill

This research aims to obtain infomation about Arabic learning especially speaking skill in Arabic Language Education Department at IAIN Batusangkar. The research uses a quantitative approach. The instruments to collect the data are test and questionnaire. The data were analyzed using descriptive statistics. The results of the research state that the students’ speaking ability at class “ A “ are 28% low, 36% moderate, and 36% high. While, at class “B”, students’ speaking abilities are 36.4% low, 40,9% moderate, and 22.7% high. The cause of students’ low ability is the unappropriateness of teachers’ strategy in teaching speaking. There are about 96% students at class “A” agreed and 86.4% students at class “B” had similar answer. Another cause is students’ low motivation in learning. Class “A” students agreed for about 76% of them and 77% of class “B” students answered the same. From the finding, it can be concluded that the inability of students to speak Arabic can be overcomed by improving teaching strategies and encouraging maximum motivation  to learn Arabic.

Direct observation of long chain enrichment in flow-induced nuclei from molecular dynamics simulations of bimodal blends

Soft Matter ◽  
2021 ◽  
Vol 17 (10) ◽  
pp. 2872-2882
Author(s):  
Muhammad Anwar ◽  
Richard S. Graham
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Direct Observation ◽  
Dynamics Simulations ◽  
Long Chain ◽  
Long Chains

Modelling of flow-induced nucleation in polymers suggest that long chains are enriched in nuclei, relative to their melt concentration.

scholarly journals Some kinematics of halo coronal mass ejections

2020 ◽  
Vol 29 (1) ◽  
pp. 81-88
Author(s):  
Virendra Kumar Verma ◽  
Nishant Mittal ◽  
Ramesh Chandra
Keyword(s):  
Coronal Mass Ejections ◽  
Solar Flares ◽  
Coronal Holes ◽  
Geomagnetic Disturbances ◽  
Class A ◽  
Heliospheric Physics ◽  
Class B ◽  
The Mean ◽  
Class C

AbstractWe present an investigation of halo coronal mass ejections (HCMEs) kinematics and other facts about the HCMEs. The study of HCMEs is very important because HCMEs are regarded as the main causes of heliospheric and geomagnetic disturbances. In this study, we have investigated 313 HCMEs observed during 1996-2012 by LASCO, coronal holes, and solar flares. We find that HCMEs are of two types: accelerated HCMEs and decelerated HCMEs. The mean space speed of HCMEs is 1283 km/s while the mean speed of decelerated HCMEs and accelerated HCMEs is 1349 km/s and 1174 km/s, respectively. The investigation shows that 1 (0.3%) HCME was associated with class A SXR, 14 (4.7%) HCMEs were associated with class B SXR-flares, 87 (29.4%) HCMEs were associated with class C SXR-flares, 125 (42.2%) HCMEs were associated with class M SXR-flares and 69 (23.3%) HCMEs were associated with class X SXR-flares. The speed of HCMEs increases with the importance of solar SXR-flares. The various results obtained in the present analysis are discussed in the light of the existing scenario of heliospheric physics.

scholarly journals Design and Validation of an Adjustable Large-Scale Solar Simulator

2021 ◽  
Vol 11 (4) ◽  
pp. 1964
Author(s):  
Daniele Colarossi ◽  
Eleonora Tagliolini ◽  
Paolo Principi ◽  
Roberto Fioretti
Keyword(s):  
Large Scale ◽  
Design Procedure ◽  
Spatial Arrangement ◽  
Luminous Flux ◽  
International Electrotechnical Commission ◽  
Solar Simulator ◽  
Class A ◽  
Pv Panel ◽  
Temporal Instability ◽  
Class B

This work presents an adjustable large-scale solar simulator based on metal halide lamps. The design procedure is described with regards to the construction and spatial arrangement of the lamps and the designed optical system. Rotation and translation of the lamp array allow setting the direction and the intensity of the luminous flux on the horizontal plane. To validate the built model, irradiance nonuniformity and temporal instability tests were carried out assigning Class A, B, or C for each test, according to the International Electrotechnical Commission (IEC) standards requirements. The simulator meets the Class C standards on a 200 × 90 cm test plane, Class B on 170 × 80 cm, and Class A on 80 × 40 cm. The temporal instability returns Class A results for all the measured points. Lastly, a PV panel is characterized by tracing the I–V curve under simulated radiation, under outdoor natural sunlight, and with a numerical method. The results show a good approximation.

scholarly journals Stereospecific Hydroxylation of Long Chain Compounds by a Species of Torulopsis

1969 ◽  
Vol 244 (4) ◽  
pp. 882-888 ◽  
Author(s):  
E Heinz ◽  
A P Tulloch ◽  
J F T Spencer
Keyword(s):  
Chain Compounds ◽  
Long Chain

scholarly journals Image data of crumb structure of bread from flour of czech spring wheat cultivars

2011 ◽  
Vol 22 (No. 4) ◽  
pp. 133-142 ◽  
Author(s):  
I. Švec ◽  
M. Hrušková
Keyword(s):  
Image Analysis ◽  
Image Data ◽  
Analysis Data ◽  
Wheat Cultivars ◽  
Rheological Measurements ◽  
Class A ◽  
Bread Volume ◽  
Class B ◽  
Crumb Structure

Abstract: Baking quality of flour from six wheat cultivars (harvest 2002 and 2003), belonging to the quality classes A and B, was evaluated using the fermented dough test. Analytical traits of kernel and flour showed differences between the classes which were confirmed by the baking test with the full-bread-formula according to Czech method. In addition to standard methods of the bread parameters description (specific bread volume and bread shape measurements) rheological measurements of penetrometer and image analysis were used in effort to differentiate wheat samples into the quality classes. The results of the baking test proved significant differences in specific bread volumes &ndash; the highest volume in class A was obtained with the cultivar Vinjet and in class B with SG-S1098 &ndash; approx. 410 and 420 ml/100 g. Although significant correlations among image analysis data and specific bread volume having been proved, any image analysis parameter did not distinguish the quality classes. Only the penetronetric measurements made with bread crumb were suitable for such purpose (r = 0.9083; for  = 0.01). Among image analysis data the total cell area of the crumb had the strongest correlation with specific bread volume (r&nbsp;=&nbsp;0.7840; for &alpha; = 0.01). &nbsp; &nbsp;

Sign in / Sign up

Export Citation Format

Share Document