Cis Junction Research Articles

An accurate one-diode model suited to represent the current-voltage characteristics of crystalline and thin-film photovoltaic modules

In this paper a new one-diode model, conceived in order to be used to represent the current-voltage curves of both crystalline and thin-film photovoltaic modules, is presented. The model parameters are calculated from the information contained in the datasheets issued by manufactures by means of simple iterative procedures that do not require the assumption of simplifying hypotheses. Some innovative relations describing the dependence of the parameters from the solar irradiance and cell temperature are adopted in order to permit the model to reliably simulate the electrical behaviour of photovoltaic devices operating in real conditions.The ability of the model to calculate the current-voltage characteristics issued by manufacturers for values of the solar irradiance and cell temperature also far from the standard rating conditions was verified for various photovoltaic technologies, such as monocrystalline, polycrystalline, amorphous silicon, CIS, CIGS and tandem junction photovoltaic modules. The percentage ratio of the mean absolute difference of current to the rated current at the maximum power point ranges from 0.071% to 1.807%; the analogous ratio of power varies between 0.056% and 1.720%. A comparison with the results obtained with other recognised two-diode models is also presented.

Reaction of levoglucosenone with (±)-α-terpineol and its acetate

In continuation of our studies [1, 2], we focused on the potential of levoglucosenone in the synthesis of menthane derivatives as a separate problem and examined the possibility for direct introduction of a menthane fragment into levoglucosenone molecule via reaction with (±)-α-terpineol. A short synthetic route to (±)-α-terpineol is the twostep procedure utilizing large-scale initial compounds, isoprene and methyl acrylate [3]. The transformation of (±)-α-terpineol into a chiral subunit requires its preliminary optical resolution and introduction of functional groups that could ensure subsequent transformations. It is known that dehydration of α-terpineol leads to the formation of a number of isomeric dienes, including α-terpinene whose yield in some cases attains 25% [4]. The use of such a mixture of menthane derivatives as diene component and of levoglucosenone as dienophile is attractive from the viewpoint of simultaneous solution of both problems. For this purpose, a toluene solution of levoglucosenone and diene mixture obtained from (±)-α-terpineol according to the procedure described in [4] was heated at 160°C in a sealed glass ampule (metohd a). In fact, after 9 h, we succeeded in isolating from the reaction mixture Diels–Alder adduct V in 3% yield [calculated on the initial (±)-α-terpineol]. Increase of the reaction time reduced the yield of V, and we failed to detect it in the reaction mixture after 30 h, presumably because of its decomposition. We also tried to use as starting compounds (±)-α-terpineol (I) and (±)-α-terpinyl acetate (II), expecting generation of α-terpinene (III) in situ under the given Diels–Alder reaction conditions. In the first case, no cycloaddition products were detected in the reaction mixture, and in the second case adduct V was formed in 4% yield in 28 h (method b). The structure of V was determined on the basis of the H and C NMR data. The coupling constant between 5a-H and 9a-H equal to 8.6 Hz indicates cis junction of the bicyclo[2.2.2]octane and pyran fragments. The signal assignment was confirmed by the HMBC technique. The 9a-H proton (δ 1.87 ppm) showed couplings with C (δC 68.29 ppm), C (49.29), C (200.96), C (138.26), and C (35.59), and cross-peaks of 5a-H (δ 2.90 ppm) with C, C (δC 44.98 ppm), C (135.53), and C (20.80) were

Unexpected different chemoselectivity in the aerobic oxidation of methylated planar catechin and bent epicatechin derivatives catalysed by the Trametes villosa laccase/1-hydroxybenzotriazole system

Unreported methylated catechin and epicatechin derivatives 5 and 6 were synthesized by an oxa-Pictet-Spengler reaction. Catechin 5 shows the B and C rings coplanar because of the formation of a trans junction between the C ring and the newly generated six-term cycle D, in turn condensed to ring B. In contrast, epicatechin 6 presents a bent geometry due to the establishment of a cis junction between the C ring and the newly formed cycle D. The oxidation of compounds 5 and 6 in the presence of the Trametes villosa laccase/1-hydroxybenzotriazole (HBT) system was investigated under aerobic conditions in both a biphasic system and a reverse micelle. The unexpected different chemoselective oxidation at the benzylic position of catechin and epicatechin derivatives 5 and 6 has been rationalized using a molecular modelling approach. These results demonstrate that the Trametes villosa laccase/HBT system represents a useful tool to functionalize the C-2 or C-4 position of phenolic compounds depending on the structural features.

ChemInform Abstract: Crystal and Molecular Structure of 18α-Glycyrrhetinic Acid

The crystal structure of 18α-glycyrrhetinic acid (trans junction of the D/E rings) has been determined in order to compare its stereochemical features with those of the known 18β form (cis junction of the D/E rings). The two stereoisomers exhibit different physiological actions. A comparison of their common moieties shows significant differences between the conformations of the unsaturated C ring, with some torsion angles differing by more than ten degrees. Further differences involve the convexity of the ABCD region, which in the α form is smaller than that observed in the β isomer, and smaller than that reported for the mean steroid configuration.

1α,6β,7β,11α,15β-Pentahydroxy-7α,20-epoxy-ent-kaur-16-ene

The title compound, C20H30O6, a natural ent-kaurane diterpenoid, named nervosanin B, was obtained from the medicinal plant Isodon serra. It is composed of four rings with the expected trans and cis junctions. One of the six-membered rings is in a chair conformation, the other two are in boat conformations and the five-membered ring adopts an evenlope conformation. The mol­ecules stack along the a axis and are linked together by inter­molecular O—H⋯O hydrogen bonds. Two intramolecular O—H⋯O interactions also occur.

Carexanes from Carex distachya Desf.: revised stereochemistry and characterization of four novel polyhydroxylated prenylstilbenes

Carexanes are unusual secondary metabolites isolated from the herbaceous plant Carex distachya. Four new carexanes have been isolated and characterized from the methanolic leaf extract of the plant. All of the structures have been elucidated on the basis of spectroscopic data. The stereochemistry of all the carexane metabolites isolated from the plant, as well as their 1H and 13C NMR spectroscopic assignment, has been revised on the basis of X-ray analysis of carexane D, chemical correlations, and NOESY/ROESY experiments. All the data suggested a cis junction between B and C rings.

3α,7α,12α-Triformyloxy-24-nor-5β-chol-22-ene

The title compound, C26H38O6, has a cis junction between two of the six-membered rings (A and B). All three of the six-membered rings have chair conformations that are slightly flattened and the five-membered ring has an unusual 13β-envelope conformation. The 7α and 12α ring substituents are both axial and the 3α and 17β groups are equatorial and pseudo-equatorial, respectively. The 3α-formyloxy group is involved in one weak intermolecular C—H...O bond, which links the molecules into dimers in a head-to-head fashion.

Conformations of three heterocyclic perhydropyrrolobenzofurans and polymeric assemblyviaco-operative intermolecular C—H...O hydrogen bonds

In 1-cyclohexyl-6,6,8a-trimethyl-3a,6,7,8a-tetrahydro-1H-1-benzofuro[2,3-b]pyrrole-2,4(3H,5H)-dione, C19H27NO3, (I), and the isomorphous compounds 6,6,8a-trimethyl-1-phenyl-3a,6,7,8a-tetrahydro-1H-1-benzofuro[2,3-b]pyrrole-2,4(3H,5H)-dione, C19H21NO3, (II), and 6,6,8a-trimethyl-1-(3-pyridyl)-3a,6,7,8a-tetrahydro-1H-1-benzofuro[2,3-b]pyrrole-2,4(3H,5H)-dione, C18H20N2O3, (III), the tetrahydrobenzo-dihydrofuro-pyrrolidine ring systems are folded at the cis junction of the five-membered rings, giving rise to a non-planar shape of the tricyclic cores. The dihydrofuran and pyrrolidine rings in (I) are puckered and adopt an envelope conformation. The cyclohexene rings adopt a half-chair conformation in all the molecules, while the substituent N-cyclohexyl ring in (I) assumes a chair form. Short intramolecular C-H...O contacts form S(5) and S(6) motifs. The isomorphous compounds (II) and (III) are effectively isostructural, and aggregate into chains via intermolecular C-H...O hydrogen bonds.

1-Isopropyl-6,6,8a-trimethyl-1,3a,5,6,7,8a-hexahydro-3H-1-benzofuro[2,3-b]pyrrole-2,4-dione

The crystal structure of the title benzofuran derivative, C16H23NO3, has been elucidated. The tricyclic core, i.e. the tetrahydrobenzo–dihydrofuro–pyrrolidine ring system, is non-planar owing to the folding of the five-membered rings at their cis junction. The cyclohexene ring assumes a half-chair conformation, while the dihydrofuran and pyrrolidine rings each adopt an envelope conformation. Intramolecular C—H...O hydrogen bonds form S(6) closed patterns.

New Tandem Reactions of Metal Carbenoids. Intermolecular Formation of Azomethine Ylide from Methyl 2‐Diazo‐2‐phenylacetate and Schiff Base: Intramolecular 1,3‐Dipolar Cycloaddition.

AbstractFor Abstract see ChemInform Abstract in Full Text.

New Tandem Reactions of Metal Carbenoids. Intermolecular Formation of Azomethine Ylide from Methyl 2-Diazo-2-phenylacetate and Schiff Base: Intramolecular 1,3-Dipolar Cycloaddition

Rhodium acetate-catalyzed decomposition of methyl 2-diazo-2-phenylacetate in the presence of substituted N-methylbenzylideneamines possessing an activated alkenyl fragment (dipolarophile) in the side chain gives products of intramolecular cycloaddition of intermediate Z,E- and E,Z-azomethine ylides. The cycloaddition is regioselective, and the products are hexahydrochromeno[4,3-b]pyrrole derivatives. The stereoselectivity of the process depends on the temperature. In the temperature range from 20 to 80°C, the major stereoisomer is that with cis junction of the tetrahydropyran and pyrrolidine rings. N-Phenylazomethine ylides generated from methyl 2-diazo-2-phenylacetate and alkyl 4-[2-(phenyliminomethyl)phenoxy]-2-butenoates at 40°C undergo cyclization to aziridines at a higher rate, as compared to the rate of cycloaddition to the internal dipolarophile. N-Phenylazomethine ylides generated by thermolysis of the corresponding aziridine or by the “deprotonation” method react with equal regio- and stereoselectivity to give intramolecular cycloaddition products, hexahydrochromeno[4,3-b]pyrrole derivatives with trans-fused tetrahydropyran and pyrrolidine rings. Analysis of the experimental and calculation data suggests preference of the endo transition state in the cycloaddition of the examined azomethine ylides.

2,4,6-Trinitro-2,4,6,8-tetraazabicyclo[3.3.0]octan-7-one

The structure of 2,4,6-tri­nitro-2,4,6,8-tetra­aza­bi­cyclo­[3.3.0]­octan-7-one, C4H5N7O7, is reported. The mol­ecule contains two unsymmetrically substituted planar fused five-membered rings with a cis junction between them.

2,5,7-Trinitro-2,5,7,9-tetraazabicyclo[4.3.0]nonan-8-one

The structure of the title compound, C5H7N7O7, contains fused five- and six-membered rings in a flattened envelope and a twist-boat conformation, respectively, with a cis junction between the two heterocyclic rings.

3 beta,7 alpha,12 alpha-triformyloxy-24-nor-5 beta-chol-22-ene.

The title compound, alternatively called 24-nor-5 beta-chol-22-ene-3 beta,7 alpha,12 alpha-triyl triformate, C(26)H(38)O(6), has a cis junction between two of the six-membered rings. All three of the six-membered rings have chair conformations that are slightly flattened and the five-membered ring has a 13 beta,14 alpha-half-chair conformation. The 3 beta, 7 alpha and 12 alpha ring substituents are axial and the 17 beta group is equatorial. The 3 beta-formyloxy group is involved in one weak intermolecular C-H...O bond, which links the molecules into dimers in a head-to-head fashion.

Structure, absolute configuration, and conformation of the antimalarial drug artesunate

The crystal and molecular structure of the antimalarial compound artesunate has been determined by direct methods. Crystals are orthorhombic, P212121, a = 9.8371(12), b = 10.517(2), c = 18.7594(5) A, Z = 4, Dc = 1.316 mg/mL. The molecule is comprised of a fused ring system containing a six-membered ring C which includes an oxygen bridge and a peroxy bridge. The 9-atom oxygen–carbon chain from O(5)—C(12)... to ... O(2)—C(6) displays a striking sequence of short, long, short, long ... bonds while these distances are all within the ranges of a normal single bond or partial double bond. It is proposed that this pattern is caused by the delocalization of the lone pair electrons on the oxygen atoms. The ring C has a distorted boat conformation and the C—O—O—C torsion angle is 46.3(2)°. Rings A and D have ideal chair conformations. Ring junctions A/B and A/D are cis junctions, B/D and C/D are trans. Packing of the molecules is stabilized by one strong hydrogen bond involving the hydroxyl group on the ester linkage and the oxygen atom of the lactone ring.

Base treatment of kobusone revisited

Abstract The caryophyllene derived epoxy ketone, kobusone, is transformed by treatment with ethanolic potassium hydroxide, into two ketols. Although the published structure of the major compound is correct, the minor product is now shown to contain a trans fused cyclopropane ring rather than the previously reported cis junction. This cyclopropyl keto alcohol shows an unusual propensity for reduction, being converted to a diol by prolonged treatment with ethanolic KOH.

Crystal and molecular structure of 18α-glycyrrhetinic acid

The crystal structure of 18α-glycyrrhetinic acid (trans junction of the D/E rings) has been determined in order to compare its stereochemical features with those of the known 18β form (cis junction of the D/E rings). The two stereoisomers exhibit different physiological actions. A comparison of their common moieties shows significant differences between the conformations of the unsaturated C ring, with some torsion angles differing by more than ten degrees. Further differences involve the convexity of the ABCD region, which in the α form is smaller than that observed in the β isomer, and smaller than that reported for the mean steroid configuration.

An NMR and theoretical study of the conformation and internal flexibility of butaclamol hydrochloride

A theoretical (MM2) and experimental (1H and 13C NMR) study of butaclamol hydrochloride in CDCl3 has been done in order to determine preferred conformations and internal molecular flexibility of this molecule. The theoretical calculations suggest the presence of four low-energy conformations, two of which involve a trans junction of the D and E rings, with the other two involving a cis I ring junction. An alternative cis junction (cis II) was excluded on energetic grounds. The 1H NMR data strongly suggest the presence of a trans D-E ring junction and are consistent with a chair conformation of the E ring. 13C spin-lattice relaxation time measurements show that most of the molecule is rigid, although there is some degree of mobility in the seven-membered B ring, associated with rapid flipping of the bridging C8 and C9 carbons between two skewed conformations, which have previously been referred to as conformer A and conformer B (Laus et al. Heterocycles 1984, 22, 311).

Elimination of c-6-hydrogen during the formation of ecdysteroids from cholesterol in Locusta migratoria ovaries

Being administered to Locusta migratoria adult females, [6- 3H, 4- 14C]cholesterol was incorporated into ecdysone and 2-deoxyecdysone. The ratio of 3H/ 14C of the two ecdysteroids isolated from newly laid eggs revealed that C-6-hydrogen of cholesterol was eliminated during the conversion to ecdysteroids in the ovaries of the insects. Thus, a hypothetical mechanism involving migration of the C-6-hydrogen to the C-5 position in the formation of A/B cis junction turned out to be less likely.

Synthesis of putative precursors of ecdysone. Part 3. Synthesis of 3β, 14α, 25-trihydroxy-5β-cholest-7-en-6-one

We describe here the first synthesis of 2, 22-dideoxyecdysone (3)(3β, 14α, 25-trihydroxy-5β-cholest-7en-6-one), a putative precursor in the biosynthesis of ecdysone (1). All the intermediates synthesized have a cis junction of the A/B rings (5β-H configuration).