Trans Equilibrium Research Articles

Hydrogenation of Edible Oils and Fats by Nickel Catalysts. I.

Modes of hydrogenation of edible oils and fats were investigated for an estimation of triacylglcerol composition of hydrogenated oil. From the data obtained, the rate o hydrogenation showed no difference in acyl positions and was directly proportional to their unsaturation degree. On the other hand, the formation of trans isomer was essentially the same in 1, 3-and 2-position and was proportional to the decrease of iodine value up to traps equilibrium value, and then the trans isomer decreased with the decrease of iodine value. The selectivities in 2-position tended slightly low, but they were negligible for the estimation of triacylglycerol composition in this report. From the results obtained the authors assume as follows. 1. Hydrogenation with nickel catalysts is the first-order consecutive reaction, and there are no difference in rate of hydrogenation and selectivities (S31, S21) between acyl positions. 2. The trans isomerization is not affected with acyl position, and is in proport on to trans isomerization ratio (TI = Δtrans/ ΔIV) dependent on hydrogenating condition and the traps isomer decreases with iodine value from trans equilibrium value. 3. There is no migration of acyl position during hydrogenation. Using S31, S21 and TI obtained experimentally, fatty acid composition and iodine value of hydrogenated oil were calculated by this simulation. Morever, saturated (S), trans unsaturated (E) and cis unsaturated (U) acid in acyl positions were calculated by this simulation. From the S, E and U calculated, the triacylglycerol compositions of hydrogenated soybean oil, cottonseed oil and rapeseed oil were estimated and illustrated by diagrams.

Hydrogenation of Edible Oils and Fats by Nickel Catalysts. II.

Modes of hydrogenation of edible oils and fats were investigated for an estimation of triacylglcerol composition of hydrogenated oil. From the data obtained, the rate o hydrogenation showed no difference in acyl positions and was directly proportional to their unsaturation degree. On the other hand, the formation of trans isomer was essentially the same in 1, 3-and 2-position and was proportional to the decrease of iodine value up to traps equilibrium value, and then the trans isomer decreased with the decrease of iodine value. The selectivities in 2-position tended slightly low, but they were negligible for the estimation of triacylglycerol composition in this report. From the results obtained the authors assume as follows. 1. Hydrogenation with nickel catalysts is the first-order consecutive reaction, and there are no difference in rate of hydrogenation and selectivities (S31, S21) between acyl positions. 2. The trans isomerization is not affected with acyl position, and is in proport on to trans isomerization ratio (TI = Δtrans/ ΔIV) dependent on hydrogenating condition and the traps isomer decreases with iodine value from trans equilibrium value. 3. There is no migration of acyl position during hydrogenation. Using S31, S21 and TI obtained experimentally, fatty acid composition and iodine value of hydrogenated oil were calculated by this simulation. Morever, saturated (S), trans unsaturated (E) and cis unsaturated (U) acid in acyl positions were calculated by this simulation. From the S, E and U calculated, the triacylglycerol compositions of hydrogenated soybean oil, cottonseed oil and rapeseed oil were estimated and illustrated by diagrams.

Tetracarbonylwolfram-komplexe mit zwei unterschiedlichen donorliganden : I. Darstellung und mechanismus der thermischen isomerisierung

cis- and trans-tetracarbonyltungsten complexes (R 3P)(R′ 3E)W(CO) 4 (R 3P,R′ 3E = i-Pr 3P, Ph 2-i-PrP, Ph 3P, Ph 2HP, (Me 2n) 3P, Ph(i-PrO) 2P, (i-PrO) 3P, (PhO) 3P, Ph 3As, Ph 3Sb) are obtained from the chlortetracarbonyltungstates [(R 3P)W-(CO) 4Cl] - by several different routes. a cis—trans equilibrium is attained at 20–30°C with the trans isomer being thermodynamically more stable in nearly all cases. The cis-trans isomerisation of the phosphine—arsine and phosphine—stibine complexes is shown by ligand exchange experiments to occur via dissociation of the arsine and stibine ligand, respectively. The bis(phosphine) complexes, however, isomerise intramolecularly without bond cleavage.

Dielectric Measurements and Molecular Structure. Thermodynamic Parameters in Conformational Equilibria of α-Diazoketones

Abstract The electric dipole moments of acetyldiazomethane (MeCOCHN2) and 1-acetyl-1-diazo-ethane (MeCOMeN2) between 10 and 70 °C have been measured. Using appropriate group and bond moments, the concentrations of the two rotamers present in each have been calculated and, hence, the equilibrium constant for the cis ⇆ trans equilibrium at the various temperatures. The change in standard enthalpy (⊿H°), standard free energy (⊿G°) and standard entropy (⊿S°) are reported for the conversion of one mole of cis isomer to trans isomer.

A general kinetic analysis of transport Tests of the carrier model based on predicted relations among experimental parameters

The analysis of transport kinetics has lacked both a unified treatment in which general rate equations are written entirely in terms of experimental parameters, and a convention by which these parameters may be designated in a concise yet immediately recognizable manner. Such a treatment is presented here in an easily accessible form, and a simple system of nomenclature is proposed resembling that in use in enzyme kinetics. The treatment is independent of assumptions about rate-limiting steps in transport, and applies to both active and facilitated systems, including obligatory exchange. A single substrate is characterized by twelve different parameters, only five of which are required in theory to calculate the others. If a second substrate is present on the trans side of the membrane there are six more parameters. All eighteen parameters are linked by multiple relationships which provide a complete set of rejection criteria for the generalized form of the mobile carrier. Relationships among parameters are also defined that give information on the rate-limiting steps in transport. Equations governing any individual experiment, involving only experimental parameters, are easily written out from the general expressions, for example under conditions of zero trans and infinite trans flux, equilibrium exchange, or competitive inhibition.

Empirical atom—atom potential calculations on histamine and 4-methylhistamine

Empirical atom—atom potential calculations for the mono- and dications of histamine and the monocation of 4-methylhistamine have been made. The isolated molecule model, including the electrostatic interaction, satisfactorily reproduce the experimental results obtained in crystals by X-ray diffraction for the histamine dication, but not for the histamine monocation. In order to show the effect of hydration of the species in solution, it was assumed that hydration should eliminate electrostatic interaction and calculations on molecules without charges were made, obtaining an excellent agreement between the calculated values of molar fractions of the gauche— trans equilibrium and the experimental results determined by NMR. On the basis of the results obtained, it is proposed that mobile gauche and trans conformations would be active with H 1 receptors whereas fairly rigid gauche conformations would be active with H 2 receptors.

Dynamic proton magnetic resonance studies on complex spin systems. Non‐mutual three‐spin exchange in N‐(trideuteriomethyl)‐2‐cyanoaziridine

AbstractAt room temperature and below, the proton NMR spectrum of N‐(trideuteriomethyl)‐2‐cyanoaziridine consists of two superimposed ABC patterns assignable to two N‐invertomers; a single time‐averaged ABC pattern is observed at 158.9°C. The static parameters extracted from the spectra in the temperature range from –40.3 to 23.2°C and from the high‐temperature spectrum permit the calculation of the thermodynamic quantities ΔH0 = −475±20 cal mol−1 (−1.987 ± 0.084 kJ mol−1) and ΔS0 = 0.43±0.08 cal mol−1 K−1 (1.80±0.33 J mol−1 K−1) for the cis ⇌ trans equilibrium. Bandshape analysis of the spectra broadened by non‐mutual three‐spin exchange in the temperature range from 39.4–137.8°C yields the activation parameters ΔHtc≠ = 17.52±0.18 kcal mol−1 (73.30±0.75 kJ mol−1), ΔStc≠ = −2.08±0.50 cal mol−1 K−1 (−8.70±2.09 J mol−1 K−1) and ΔGtc≠ (300 K) = 18.14±0.03 kcal mol−1 (75.90±0.13 kJ mol−1) for the trans → cis isomerization. An attempt is made to rationalize the observed entropy data in terms of the principles of statistical thermodynamics.

Some four- and five-co-ordinate cations of platinum(II) containing alkylphosphine and hydride ligands

Hydrogen-1 and 31P n.m.r. spectroscopy have been used to study the equilibrium of trans-[PtH(I)(PEt3)2] with an additional phosphine L [mol ratio 1 : 1, L = PMe3-nHn(n= 0–3) or PEt3] in CD2Cl2 solution. The spectra are temperature dependent and the cation [PtH(PEt3)2L]+ is observed at –90 °C. These cations (except L = PH3) have been isolated as [BPh4]– salts from reactions in methanol. A mixture of trans-[PtH(I)(PEt3)2] and PMeH2(mol ratio 1 : 2) gives completely reversible temperature-dependent n.m.r. spectra from which the formation of [PtH(PMeH2)2(PEt3)2]+ is inferred. Reaction of [PtH(PEt3)3]+ with PMeH2, PMe2H, or PMe3 at –90 °C in CD2Cl2 gives well resolved spectra of [PtH(PEt3)L3]+. The spectra show the five-co-ordinate cations to have a trigonal-bipyramidal structure with the PEt3 groups in equatorial positions.

Nickel(II) compounds of three homologous linear tetra-amines, especially solvent effects and configuration

Abstract A comparative study has been made of the 1:1 nickel(II) compounds of three homologous linear tetraamines: 1,4,7,10-tetraazadecane(trien), 1,4,8,11- tetraazaundecane(2,3,2-tet), and 1,5,8,12-tetraazodecane(3,2,3-tet). A range of solid compounds Ni(tetraamine)X 2 (X = Cl, Br, I, NCS, NO 2 , NO 3 , Clo 4 ), a number of which are new, has been prepared from 2,3,2-tet and 3,2,3-tet. These include the structural isomers yellow low-spin [Ni(3,2,3-tet)]I 2 ] and lilac high-spin trans -[Ni(3,2,3-tet)]I 2 ]. The high-spin species have a trans octahedral configuration, except for [Ni(2,3,2-tet)NO 3 ]NO 3 , which appears to have a chelating nitrate. In solution in water, DMF, and DMSO two equilibria of these compounds have been studied under varying conditions: (a) the cis ⇄ trans equilibria of the high-spin [Ni(N 4 )(S) 2 ] 2+ species (S = solvent); and (b) high spin octahedral ⇄ low-spin planar equilibria. It is shown for the first time that equilibria (a) occur in such solutions for both 2,3,2-tet and 3,2,3-tet. The trans isomers are preferred over cis in the orders: (i) (for solvent) H 2 O > DMF > DMSO; and (ii) (for the amines) 3,2,3-tet > 2,3,2-tet ⪢ trien. In concentrated LiNO 3 and LiClO 4 , Ni(trien) 2+ , but not the others, forms high spin cis -[Ni-(N 4 )O 2 ] species which apparently have a chelating anion. For equilibria (b) (the singlet ⇄ triplet equil.) the planar low-spin species are preferred in the order 2,3,2-tet > 3,2,3-tet > trien — an order different from that observed in (a). Difficulties in defining ϵ max for these low-spin species, and hence in quantifying the equilibria are discussed with evidence for the complication. The observations on both equilibria can be rationalised by reference to the steric effects of the amines: 3,2,3-tet has a greater preference thatn 2,3,2-tet for trans high-spin isomers, but it can less easily accomodate to the shorter NiN bond lengths in the low-spin species.

Adducts of tin(IV) tetrahalides with neutral Lewis bases. II. Quantitative study of the Cis- trans equilibria by NMR

The cis- trans of SnX 4·2L and SnX 4·LL adducts in solution were studied quantitatively by 19F, 31P and 1H NMR spectroscopy ( X = F, Cl, Br; L = Me 2O, Et 2O, Me 2S, Et 2S, Me 2Se, MeCN, Me 3CCN, Me 2CO, TMPA, Me 2N(MeO) 2PO, HMPA; LL = (MeOCH 2−) 2). The relative stabilities for cis-and trans-SnX 4·2L adducts were estimated, and the following sequence obtained: HMPA > Me 2N(MeO) 2PO > TMPA Me 2Se > Me 2S > Me 2O. The existence of SnCl 4·L a·L b mixed species when tin tetrachloride is present with two different ligands has been shown, and their concentrations at equilibrium obey a statistical distribution. The cis- trans isomerizationconstant is relatively independent of temperature, but depend strongly on solvent polarity, the trans isomer being favoured in weakly polar media The trends in the isomerization constant as a function of substitutions of the ligand and the halogen is discussed on the basis of tin(IV) orbital overlap.

The X‐Pro peptide bond as an nmr probe for conformational studies of flexible linear peptides

AbstractThe equilibrium between the cis and trans forms of X‐Pro peptide bonds can readily be measured in the 13C nmr spectra. In the present paper we investigate how observation of this equilibrium could be used as an nmr probe for conformational studies of flexible polypeptide chains. The experiments include studies by 13C nmr of a series of linear oligopeptides containing different X‐L‐Pro peptide bonds, with X = Gly, L‐Ala, L‐Leu, L‐Phe, D‐Ala, D‐Leu, and D‐Phe. Overall the study confirms that X‐Pro peptide bonds can generally be useful as 13C nmr probes reporting the formation of nonrandom conformation in flexible polypeptide chains. It was found that the cis–trans equilibrium of X‐Pro is greatly affected by the side chain of X and the configuration of the α‐carbon atom of X. On the basis of these observations some general rules are suggested for a practical applications of the X‐Pro nmr probes in conformational studies of polypeptide chains.

Conformational analysis by carbon-13 nuclear magnetic resonance spectroscopy. Part I. Hexahydro-3H-oxazolo[3,4-a] pyridines

Compraison of the C(3), C(1), and C(8a) chemical shifts in hexahydro-3H-oxazolo [3,4-a] pyridine with those in methyl substituted derivatives suggests its existence in solution at n.m.r. probe temperature as a cis⇌trans equilibrium mixture containing 73–78% of the trans-fused conformation; 13C–H coupling constants involving the C(3) protons are dependent upon the orientation of adjacent heteroatom lone pairs.

ChemInform Abstract: CONFORMATIONAL ANALYSIS OF HEXAHYDRO‐3H‐OXAZOLO(3,4‐C)PYRIDINES BY CARBON‐13 FOURIER‐TRANSFORM NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY

Comparison of the C(3), C(1), and C(8a) chemical shifts in hexahydro-3H-oxazolo[3,4-c]pyridine with those in anancomeric derivatives suggests its existence in solution at n.m.r. probe temperature as a cis⇌trans equilibrium mixture containing ca. 76% of the trans-fused conformation; 13C–H coupling constants involving the C(3) protons are dependent upon the orientation of adjacent lone pairs.

ChemInform Abstract: VIBRATIONAL SPECTRA, BARRIERS TO INTERNAL ROTATION AND CONFORMATION OF PROPARGYL METHYL ETHER AND METHOXYACETONITRILE

The infra-red absorption spectra of propargyl methyl ether and the isoelectronic compound methoxyacetonitrile in the vapour, liquid and solid states have been examined. The spectra of both ethers indicate the presence of a conformational equilibrium of trans and gauche forms, the latter being the more stable in both cases. Calculations of the magnitude of the barrier to rotation of the methyl group and of the barrier to rotation about the O—CH2X bond have been made for the gauche rotamer of both compounds.

Vibrational spectra, barriers to internal rotation and conformation of propargyl methyl ether and methoxyacetonitrile

The infra-red absorption spectra of propargyl methyl ether and the isoelectronic compound methoxyacetonitrile in the vapour, liquid and solid states have been examined. The spectra of both ethers indicate the presence of a conformational equilibrium of trans and gauche forms, the latter being the more stable in both cases. Calculations of the magnitude of the barrier to rotation of the methyl group and of the barrier to rotation about the O—CH2X bond have been made for the gauche rotamer of both compounds.

Conformational analysis of hexahydro-3H-oxazolo[3,4-c]pyridines by carbon-13 fourier-transform nuclear magnetic resonance spectroscopy

Comparison of the C(3), C(1), and C(8a) chemical shifts in hexahydro-3H-oxazolo[3,4-c]pyridine with those in anancomeric derivatives suggests its existence in solution at n.m.r. probe temperature as a cis⇌trans equilibrium mixture containing ca. 76% of the trans-fused conformation; 13C–H coupling constants involving the C(3) protons are dependent upon the orientation of adjacent lone pairs.

Transport of monosaccharides. I. Asymmetry in the human erythrocyte mechanism.

Transport of D-glucose across human erythrocyte membranes occurs via a facilitated diffusion process which demonstrates influx-efflux asymmetry. The mechanism of the asymmetry has been studied by estimating unidirectional fluxes in the presence or absence of trans equilibrium hexose. In the absence of transhexose, the half-saturation constant for efflux at 15 degrees C was approximately 10 mM as compared with 27 mM for influx; the corresponding values for maximal transfer rates (mumol/min per ml cell H(2)O) were approximately 51 vs. 18. The estimation of kinetic parameters, including the constant F(s), which is the ratio of maximal transfer rate/half-saturation constant, indicates a unique effect of intracellular hexose on the transfer system. Further evidence to support this conclusion was obtained by studying the effects of noncompetitive inhibitors on efflux vs. influx. N-ethylmaleimide, p-chloromercuribenzenesulfonate, and dichloroallyldiethylstilbestrol all inhibited efflux much more than influx. Glucose rendered the transport system more reactive to N-ethylmaleimide as assayed by efflux, whereas influx was much less affected. The results support the hypothesis that the transport system exists in two states. Transition from one state to the other is dependent on the presence of intracellular hexose.

V-Triazolines. Part III. cis-trans Equilibrium of 1-aryl-4,5-dihydro-v-triazoles

The stereochemical features of the reaction between 4-nitrophenyl azide and some enamines deriving from straight-chain aliphatic ketones or aryl alkyl ketones have been studied. Under kinetically controlled conditions the cis–trans equilibrium mixture of the enamine reacts with the azide, yielding exclusively the trans-triazoline. At higher temperature or in the presence of acidic catalysts, the trans-triazoline epimerizes, thus affording a cis–trans equilibrium mixture. The factors which affect the equilibrium position and the epimerization rate are discussed and a probable epimerization mechanism is suggested.

Cis–trans Equilibrium in meta-chlorophenyl aldehydes, ethers, ketones, and carboxylic esters from dipole moment studies

Comparison of dipole moments of meta-chloro-, para-chloro-, and 3,5-dichloro-substituted compounds with parents enable the calculation of group dipole directions, of interaction moments, and of cis–trans conformational equilibria in the meta-substituted derivatives.

Configuration of secondary amides and thioamides: spectroscopic and theoretical studies

Infrared spectroscopy has been employed to study the cis–trans-equilibria and ΔH values in secondary amides and thioamides. Based on these results, several generalizations have been made regarding the structural factors affecting the configurations. Solvent effects on the cis–trans-equilibria and on the barrier height to rotation in secondary amides have been investigated by i.r. and n.m.r. spectroscopy; the barrier height increases with solvent polarity. Proton-donor or -acceptor solvents significantly affect the cis–trans equilibrium in amides. Solvent effect and temperature effect studies on the n.m.r. and i.r. spectra of 8-, 9- and 13-lactams and their N-methyl derivatives show that in 9-lactam and N-methyl-13-lactam both cis- and trans-isomers are present. Molecular orbital calculations satisfactorily predict relative stabilities of the different configurations of secondary amide derivatives; oxygen protonation of amides is favoured over nitrogen protonation. In the O-protonated amides, the barrier height to rotation is appreciably larger than in the parent amides.