Olefinic Carbon Atoms Research Articles

A Computational Study of Heteroatom Analogues of Selenoxide and Selenone syn Eliminations.

Selenoxide syn elimination is a widely used method for the synthesis of alkenes because it proceeds under exceptionally mild conditions, typically with excellent regio- and stereoselectivity. Surprisingly, hetero-selenoxide eliminations, where one or both olefinic carbon atoms are replaced with heteroatoms, have been little investigated, and their selenonyl counterparts even less so. A variety of such reactions, where the heteroatoms included combinations of O, N and S, as well as C, were investigated computationally. Selenoxides typically have lower activation energies and are slightly endothermic, while the corresponding selenones display higher activation energies and are exothermic in the gas state. The results are consistent with concerted, five-centre processes, leading to the formation of dioxygen, aldehydes, diazenes and imines from seleninyl or selenonyl peroxides, esters, hydrazines and amines, respectively. The more acidic selenenyl hydrodisulfide analogue undergoes proton transfer to the basic selenoxide oxygen atom instead of concerted elimination, resulting in the formation of a zwitterion. However, the formation of the corresponding selenonyl zwitterion is disfavoured compared to concerted syn elimination. The effects of solvents were also computed along with changes in enthalpy, entropy and free energy. Solvent effects were variable, while free energy calculations indicated overall ΔG values ranging between 3.60 and -32.12 kcal mol-1 for the syn eliminations of methyl methanethioseleninate and methaneperoxyselenonic acid, respectively. These computations suggest that the olefin-forming selenoxide syn elimination may be more general than currently understood and that replacement of the two carbon atoms with heteroatoms can lead to viable processes.

Novel Unsymmetric 3,5-Bis(benzylidene)-4-piperidones That Display Tumor-Selective Toxicity.

Two series of novel unsymmetrical 3,5-bis(benzylidene)-4 piperidones 2a–f and 3a–e were designed as candidate antineoplastic agents. These compounds display potent cytotoxicity towards two colon cancers, as well as several oral squamous cell carcinomas. These compounds are less toxic to various non-malignant cells giving rise to large selectivity index (SI) figures. Many of the compounds are also cytotoxic towards CEM lymphoma and HL-60 leukemia cells. Representative compounds induced apoptotic cell death characterized by caspase-3 activation and subG1 accumulation in some OSCC cells, as well as the depolarization of the mitochondrial membrane potential in CEM cells. A further line of inquiry was directed to finding if the SI values are correlated with the atomic charges on the olefinic carbon atoms. The potential of these compounds as antineoplastic agents was enhanced by an ADME (absorption, distribution, metabolism, and excretion) evaluation of five lead molecules, which revealed no violations.

Ultrasonic extraction of oil shale bitumen and study of its structural features using GC-MS and NMR techniques

ABSTRACT Oil shale is a raw material that is considered to be an alternative fossil fuels and it is widely used in producing energy and chemicals. Oil shale bitumen identification are not widely described in literature. This article tackles the structural elucidation of oil shale bitumen using gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR) spectroscopy with a short sample preparation step, based on ultrasonic-assisted liquid extraction. The ultrasonic-assisted extraction was examined in terms of solvent type and volume, sample size, sonication time and temperatures. A bitumen recovery of 17.7 wt% dmmf (dry-mineral-matter-free) was achieved when 0.50 g of shale was mixed with 20 mL THF and sonicated for 10 min at ultrasonic power of 120 W at 45°C. GC-MS of the bitumen showed high polar oxygenated compounds with more than 20 wt% being esters and ethers. Small concentrations of thiols and amides have been also found. The structural identification of bitumen was carried out using 1H-NMR and 13C-NMR and the results showed highly aliphatic character bitumen, consisting of aromatic, paraffinic, naphthenic and olefinic hydrogen and carbon atoms. These results suggested that ultrasonic solvent extraction could be an efficient and environment-friendly method for obtaining of bitumen from oil shale.

Ultraviolet photolysis of monochloro-p-benzoquinone (MCBQ) in aqueous solution: Theoretical investigation into the dechlorination

In this work, the UV-induced transformation of monochloro-p-benzoquinone (MCBQ) in aqueous solution has been systematically investigated through quantum chemical calculations. During the UV irradiation at 253.7 nm, the first triplet state of MCBQ (3MCBQ*) was from the intersystem crossing of its first excited singlet state (1MCBQ*). In aqueous solution, the nucleophilic attack of OH− on carbon atoms in 3MCBQ* was the central reaction. The addition of OH− to olefinic carbon atoms was much more kinetically feasible than that to carbonyl carbon atoms, even though the carbonyl carbon atoms were more positively charged. Moreover, OH− preferred to add to the ortho-position of C–Cl bond, where the unchlorinated atom was more negatively charged than the chlorinated one. The UV photolysis of the primary intermediate (HO-CBQ) was not the same as that of MCBQ. The attack of OH− on the para-position of C–Cl bond was the most efficient pathway. The addition of OH− to the chlorinated atom of 3HO-CBQ* was much more efficient than that in the case of 3MCBQ*, which reveals that more UV irradiation may promote the dechlorination. The findings in the present study may be helpful to enrich the understanding of the halobenzoquinones transformation in aqueous solution.

Understanding water mediated proton migration in conversion of π-bond in olefinic carbon atoms into C–N bond to form β-amino adducts

The aza-Michael reactions with a variety of substrates were conducted in water affording the quantitative yields without any external catalyst, which is contrary to that published in literature. A more rational approach to analyze this problem was by conducting this conspicuous reaction with a variety of substrates in water and the results were analyzed using advanced theoretical calculations. Our investigation on the role of water in the reaction proposed a mechanism wherein water plays dual role both as medium as well as catalyst to facilitate the C–N bond formation using powerful tool in its armory, the “H-bonding”. Reactions were conducted in the absence of an external catalyst or co-solvents and, hence, are a greener approach in organic synthesis. The reactions of 15 examples were conducted with a variety of substrates to afford the addition products in the range of 70–95% yield. Theoretical studies on the transition state analysis suggested that it was the assistance of water, through H-bonding, that facilitated the conjugate addition of amine and proton transfer from ammonium ion, which could happen through two equally possible pathways.

Genetic regulation of scytonemin and mycosporine-like amino acids (MAAs) biosynthesis in cyanobacteria

Scytonemin and mycosporine-like amino acids (MAAs) are important novel secondary metabolites synthesized by cyanobacteria to protect themselves from lethal ultraviolet (UV) radiation. Scytonemin, the extracellular polysaccharide sheath pigment is found in several cyanobacterial species and is a lipid-soluble dimeric pigment consisting of phenolic and indolic subunits linked through an olefinic carbon atom. Structure of MAAs consists of aminocyclohexenone or an aminocyclohexinimine chrompohore conjugated with the nitrogen substituent of an amino acid or its amino alcohol. MAAs are small, colorless water soluble compounds. These UV screening compounds are highly photostable photoprotectant and also serve as potent antioxidants. Multiple environmental signals influence scytonemin and MAAs synthesis and regulation of induction of these UV screening compounds is a part of complex stress response pathway. Hence, proper understanding of genetic regulation and biosynthesis of these microbial sunscreens would not only provide scientific insight in a major class of secondary metabolites but will also help in commercial production of these new age ecofriendly sunscreens.

Regioselectivity observed in manganese(III) acetate mediated addition of acetylacetone to various alkenes: mechanistic and theoretical studies

Various alkenes substituted at the 1,2-positions by 2-thiophenyl, 3-thiophenyl, and phenyl substituted by electron-withdrawing and electron-donating groups were treated with acetylacetone in the presence of Mn(OAc)3 in acetic acid. In cases where the thiophene ring was connected at the C-2 carbon atom to the double bond, a single regioisomer was formed whereas in case of substitution at the C-3 positions two regioisomers were formed. Stilbene derivatives also gave two regioisomers under the same reaction conditions. However, 1-methoxy-4-(4-nitrostyryl)benzene provided a single cycloaddition product. The observed regioselectivity was discussed in terms of atomic charge distribution on the olefinic double bond carbon atoms. Furthermore, activation barriers for transition states were calculated.

The chemical behavior of terminally tert-butylated polyolefins.

The chemical behavior of various oligoenes 2 has been studied. The catalytic hydrogenation of diene 3 yielded monoene 4. Triene 7 was hydrogenated to diene 8, monoene 9 and saturated hydrocarbon 10. Bromine addition to 3 and 7 yielded the dibromides 17 and 18, respectively, i.e., the oligoene system has been attacked at its terminal olefinic carbon atoms. Analogously, the higher vinylogs 19 and 20 yielded the 1,8- and 1,10-bromine adduts 23 and 24, respectively, when less than 1 equivalent of bromine was employed. Treatment of tetraene 19 with excess bromine provided tetrabromide 25. In epoxidation reactions, both with meta-chloroperbenzoic acid (MCPBA) and dimethyldioxirane (DMDO) two model oligoenes were studied: triene 7 and tetraene 19. Whereas 7 furnished the rearrangement product 31 with MCPBA, it yielded the symmetrical epoxide 32 with DMDO. Analogously, 19 was converted to mono-epoxide 33 with MCPBA and to 34 with DMDO. Diels–Alder addition of 7 with N-phenyltriazolinedione (PTAD) did not take place. Extension of the conjugated π-system to the next higher vinylog, 19, caused NPTD-addition to the symmetrical adduct 37 in good yield. Comparable results were observed on adding NPTD (equivalent amount) to pentaene 20 and hexaene 21. Using 36 in excess provided the 2:1-adduct 40 from 21 and led to a complex mixture of adducts from heptaene 22. With tetracyanoethylene (TCNE) as the dienophile, tetraolefin 19 yielded the symmetrical adduct 43, although the reaction temperature had to be increased. Pentaene 20 and hexaene 21 led to corresponding results, adducts 44 and 45 being produced in acceptable yields. With nonaene 42 and TCNE the 2:1-adduct 48 was generated according to its spectroscopic data. Exploratory photochemical studies were carried out with tetraene 19 as the model compound. On irradiation this reacted with oxygen to the stable endo-peroxide 52.

DFT study of the mechanism of the phenylselenoetherification reaction of linalool

A systematic study of the mechanism of phenylselenoetherification of a naturally occurring alcohol linalool with PhSe+ was performed at the B3LYP/6-311+G(d,p) level of theory, in conjunction with the CPCM solvation model. The syn and anti reaction pathways were examined in the absence and presence of some Lewis bases (quinoline, piperidine, pyridine, and triethylamine) as catalysts. It was found that the reaction occurs via the phenylseleniranium intermediate, which further suffers a nucleophilic attack of the oxygen to two olefinic carbon atoms. This intramolecular cyclization yields 5-ethenyl-5-methyl-2-[2-(phenylseleno)-prop-2-yl]tetrahydrofuran as the major product and 6-ethenyl-2,2,6-trimethyl-3-phenylselenotetrahydropyran as the minor product. Lewis bases facilitate the reaction by strong hydrogen bonds between the alcoholic hydrogen and nitrogen of an additive moiety, and they stabilize the product complexes. Since the formation of the tetrahydrofuran derivative requires higher activation energy, but is thermodynamically more stable than the tetrahydropyran, it was concluded that the phenylselenoetherification reaction of linalool is thermodynamically controlled.

Rationalisation of the stereochemical outcome of ene-reductase-mediated bioreduction of α,β-difunctionalised alkenes

The OYE1-3-mediated reductions of some α,β-difunctionalised alkenes, showing on the double bond a nitrile and ester group, are submitted to a careful stereochemical analysis, in order to identify which of the two electron-withdrawing groups (EWGs) is responsible for the activation of the CC double bond towards reduction and for establishing hydrogen bond interactions within the binding pocket of the enzymes. The results show that for most of these substrates the activating EWG is the CN moiety linked to the prostereogenic olefinic carbon atom. The final stereochemical outcome can be explained through the empirical model which has been recently developed for difunctionalised alkenes activated by carbonyl/carboxyl containing EWGs. In a single case the activation is due to the COOR group linked to the less substituted olefinic carbon atom: an alternative empirical model is established for this kind of substrates, taking into consideration the OYE-catalysed reductions of β,β′-disubstituted-α-monofunctionalised alkenes.

High-field NMR spectroscopy and FTICR mass spectrometry: powerful discovery tools for the molecular level characterization of marine dissolved organic matter

Abstract. High-performance, non-target, high-resolution organic structural spectroscopy was applied to solid phase extracted marine dissolved organic matter (SPE-DOM) isolated from four different depths in the open South Atlantic Ocean off the Angola coast (3° E, 18° S; Angola Basin) and provided molecular level information with extraordinary coverage and resolution. Sampling was performed at depths of 5 m (Angola Current; near-surface photic zone), 48 m (Angola Current; fluorescence maximum), 200 m (still above Antarctic Intermediate Water, AAIW; upper mesopelagic zone) and 5446 m (North Atlantic Deep Water, NADW; abyssopelagic, ~30 m above seafloor) and produced SPE-DOM with near 40% carbon yield and beneficial nuclear magnetic resonance (NMR) relaxation properties, a crucial prerequisite for the acquisition of NMR spectra with excellent resolution. 1H and 13C NMR spectra of all four marine SPE-DOM showed smooth bulk envelopes, reflecting intrinsic averaging from massive signal overlap, with a few percent of visibly resolved signatures and variable abundances for all major chemical environments. The abundance of singly oxygenated aliphatics and acetate derivatives in 1H NMR spectra declined from surface to deep marine SPE-DOM, whereas C-based aliphatics and carboxyl-rich alicyclic molecules (CRAM) increased in abundance. Surface SPE-DOM contained fewer methyl esters than all other samples, likely a consequence of direct exposure to sunlight. Integration of 13C NMR spectra revealed continual increase of carboxylic acids and ketones from surface to depth, reflecting a progressive oxygenation, with concomitant decline of carbohydrate-related substructures. Aliphatic branching increased with depth, whereas the fraction of oxygenated aliphatics declined for methine, methylene and methyl carbon. Lipids in the oldest SPE-DOM at 5446 m showed a larger share of ethyl groups and methylene carbon than observed in the other samples. Two-dimensional NMR spectra showed exceptional resolution and depicted resolved molecular signatures in excess of a certain minimum abundance. Classical methyl groups terminating aliphatic chains represented ~15% of total methyl in all samples investigated. A noticeable fraction of methyl (~2%) was bound to olefinic carbon. Methyl ethers were abundant in surface marine SPE-DOM, and the chemical diversity of carbohydrates was larger than that of freshwater and soil DOM. In all samples, we identified sp2-hybridized carbon chemical environments with discrimination of isolated and conjugated olefins and α,β-unsaturated double bonds. Olefinic proton and carbon atoms were more abundant than aromatic ones; olefinic unsaturation in marine SPE-DOM will be more directly traceable to ultimate biogenic precursors than aromatic unsaturation. The abundance of furan, pyrrol and thiophene derivatives was marginal, whereas benzene derivatives, phenols and six-membered nitrogen heterocycles were prominent; a yet unassigned set of six-membered N-heterocycles with likely more than one single nitrogen occurred in all samples. Various key polycyclic aromatic hydrocarbon substructures suggested the presence of thermogenic organic matter at all water depths. Progressive NMR cross-peak attenuation from surface to deep marine SPE-DOM was particularly strong in COSY NMR spectra and indicated a continual disappearance of biosignatures as well as entropy gain from an ever increased molecular diversity. Nevertheless, a specific near-seafloor SPE-DOM signature of unsaturated molecules recognized in both NMR and Fourier transform ion cyclotron mass spectrometry (FTICR/MS) possibly originated from sediment leaching. The conformity of key NMR and FTICR/MS signatures suggested the presence of a large set of identical molecules throughout the entire ocean column even though the investigated water masses belonged to different oceanic regimes and currents. FTICR/MS showed abundant CHO, CHNO, CHOS and CHNOS molecular series with slightly increasing numbers of mass peaks and average mass from surface to bottom SPE-DOM. The proportion of CHO and CHNO negative ions increased from surface to depth, whereas CHOS and especially CHNOS molecular series markedly declined. While certain rather aliphatic CHOS and CHNOS ions were observed solely in the surface, deep marine SPE-DOM was enriched in unique unsaturated and rather oxygenated CHO and CHNO molecular series. With the exception of abyssopelagic SPE-DOM at 5446 m, which showed a peculiar CHOS chemistry of unsaturated carbon and reduced sulphur (black sulphur), CHO and CHNO molecular series contributed ~87% to total positive electrospray ionization FTICR mass peak integral, with a near constant ratio of CHNO / CHO molecular compositions near 1.13 ± 0.05. In case of all four marine SPE-DOM, remarkably disparate average elemental compositions as determined from either MS and NMR spectra were observed, caused by a pronounced ionization selectivity in electrospray ionization FTICR/MS. The study demonstrates that the exhaustive characterization of complex unknowns in marine DOM will enable a meaningful classification of individual marine biogeosignatures. Future in-depth functional biodiversity studies with a clear understanding of DOM structure and function might eventually lead to a novel, unified perception of biodiversity and biogeochemistry.

Atmospheric Fate of Methacrolein. 1. Peroxy Radical Isomerization Following Addition of OH and O2

Peroxy radicals formed by addition of OH and O(2) to the olefinic carbon atoms in methacrolein react with NO to form methacrolein hydroxy nitrate and hydroxyacetone. We observe that the ratio of these two compounds, however, unexpectedly decreases as the lifetime of the peroxy radical increases. We propose that this results from an isomerization involving the 1,4-H-shift of the aldehydic hydrogen atom to the peroxy group. The inferred rate (0.5 ± 0.3 s(-1) at T = 296 K) is consistent with estimates obtained from the potential energy surface determined by high level quantum calculations. The product, a hydroxy hydroperoxy carbonyl radical, decomposes rapidly, producing hydroxyacetone and re-forming OH. Simulations using a global chemical transport model suggest that most of the methacrolein hydroxy peroxy radicals formed in the atmosphere undergo isomerization and decomposition.

An ELF analysis of the C–C bond formation step in the N-heterocyclic carbene-catalyzed hydroacylation of unactivated C–C double bonds

The changes in electron-density along the C–C bond-formation step in the N-heterocyclic carbene-catalyzed hydroacylation of unactivated double bonds has been studied by an electron localization function (ELF) analysis at the B3LYP/6-31G** level in order to characterize the reaction mechanism. Analysis of DFT reactivity indices and the natural bond orbital and ELF analysis at the most relevant points of the intrinsic reaction coordinate indicate that the reaction path takes place through a two-stage one-step mechanism with non-polar character. In the first stage a hydrogen atom is transferred from the hydroxyl group of Breslow intermediate 12 to the terminal olefinic carbon atom, to yield a pseudodiradical species. The barrierless C–C bond formation in this species constitutes the second stage of the reaction allowing the formation of the corresponding alcohoxy intermediate 13. The present theoretical study establishes that this mechanism is completely different to that involved in the intramolecular Stetter reaction, which is initialized by a polar Michael-type addition.

Protonation of captodative trifluoromethylated aminoalkenes and isomerization of their salts. An ab initio study

A study of the regioselectivity of protonation of captodative trifluoromethylated enamines was carried out using MP2/6‐311 + G(d,p) calculations and the natural bond orbital analysis. The central issue of this research concerns the influence of the electron‐withdrawing group, which is not capable of the π,π‐conjugation, on the properties of captodative enamines and their salts. The presence of CF3 group in such type of enamines levels the energy of their N‐protonated and C‐protonated forms. The transition states were found for both intramolecular and intermolecular processes of the proton transfer. The more possible mechanism of the isomerization of enammonium and iminium cations includes the proton transfer from N‐protonated form to olefinic carbon atom of the starting enamine. The transition state energies, which correspond to intermolecular process, are relatively low (11–13 kcal mol–1) in contrast to the intramolecular pathway (64–69 kcal mol–1). Copyright © 2011 John Wiley & Sons, Ltd.

Photochemistry of Aqueous C60 Clusters: Wavelength Dependency and Product Characterization

To construct accurate risk assessment models for engineered nanomaterials, there is urgent need for information on the reactivity (or conversely, persistence) and transformation pathways of these materials in the natural environment. As an important step toward addressing this issue, we have characterized the products formed when aqueous C(60) clusters (nC(60)) are exposed to natural sunlight and also have assessed the wavelengths primarily responsible for phototransformation. Long-wavelength light (λ ≥ 400 nm) isolated from sunlight, was shown to be important in both the phototransformation of nC(60) and in the production of (1)O(2). The significance of visible light in mediating the phototransformation of nC(60) was supported by additional experiments with monochromatic light in which the apparent quantum yield at 436 nm (Φ(436 nm) = (2.08 ± 0.08) × 10(-5)) was comparable to that at 366 nm (Φ(366 nm) = (2.02 ± 0.07) × 10(-5)). LDI-TOF mass spectrometry indicated that most of the photoproducts formed after 947 h of irradiation in natural sunlight retain a 60 atom carbon structure. A combination of (13)C NMR analysis of (13)C-enriched nC(60), X-ray photoelectron spectroscopy and FTIR indicated that photoproducts have olefinic carbon atoms as well as a variety of oxygen-containing functional groups, including vinyl ether and carbonyl or carboxyl groups, whose presence destroys the native π-electron system of C(60). Thus, the photoreactivity of nC(60) in sunlight leads to the formation of water-soluble C(60) derivatives.

Formation of Osmium− and Ruthenium−Cyclobutylidene Complexes by Ring Expansion of Alkylidenecyclopropanes

Alkylidenecyclopropanes containing a chelation assistant at the terminal carbon atom of the olefinic moiety undergo an Os- or Ru-promoted ring expansion reaction to afford metal cyclobutylidene derivatives. The process occurs through a novel mechanism that implies a 1,2-migration of a CH(2) group of the three-membered ring from an olefinic carbon atom to the other one. It takes place, without direct participation of the metal, on a metallaheterocyclopentene intermediate which is generated from an eta(2)-methylenecyclopropane species stabilized by coordination of the chelation assistant.

E, E-2-Benzylidene-6-(nitrobenzylidene)cyclohexanones: Syntheses, cytotoxicity and an examination of some of their electronic, steric, and hydrophobic properties

Three series of structurally isomeric 2-benzylidene-6-(nitrobenzylidene) cyclohexanones 1– 3 were prepared and evaluated against human Molt/C8 and CEM T-lymphocytes as well as murine L1210 cells. The IC 50 values of the majority of compounds are less than 10 μM and in some assays, the figures for 1d and 1e are submicromolar. Correlations were discerned between cytotoxic potencies and the atomic charges on one of the olefinic carbon atoms, the torsion angles between an aryl ring, and the adjacent unsaturated group as well as log P values. Three representative compounds were examined for their effect on respiration in rat liver mitochondria.

Aglycone geniposidic acid, a naturally occurring crosslinking agent, and its application for the fixation of collagenous tissues

A natural compound, aglycone geniposidic acid (aGSA), originated from the fruits of Gardenia jasminoides ELLIS was used for the fixation of collagenous tissues. The presumed crosslinking reaction mechanism of collagenous tissues with aGSA was inferred by reacting aGSA with a bifunctional amine, 1,6-hexanediamine, using a series of (1)H NMR, FT-IR, and UV/Vis spectra analyses. aGSA reacted with 1,6-hexanediamine by a nucleophilic attack on the olefinic carbon atom at C-2 of deoxyloganin aglycone, followed by opening the dihydropyran ring to form heterocyclic amine compounds. It is inferred that aGSA may form intramolecular and intermolecular crosslinks with a heterocyclic structure within collagen fibers in tissues. The degrees of tissue fixation by aGSA at different pH values were investigated by examining the fixation indices and denaturation temperatures of test samples. It was found that the fixation indices and denaturation temperatures of test samples fixed at neutral or basic pH (pH 7.4 or pH 8.5) were significantly greater than at acidic pH (pH 4.0). The results obtained in this study may be used to elucidate the crosslinking mechanism and optimize the fixation process for developing bioprostheses fixed by aGSA.

Stereoselective Synthesis of Spiro-Lactones Possessing Cyclopropane Rings through Electroreductive Cross Coupling of Styrene Derivatives with Diphenyl Succinate or Glutarate

Electroreduction of α-alkylated styrenes (1) in the presence of diphenyl succinate (2) or glutarate (3) in N,N-dimethylformamide (DMF) using an undivided cell equipped with Zn plates as the anode and the cathode brought about regio- and stereoselective efficient double carbon-carbon bond formation between the two olefinic carbon atoms of 1 and one carbonyl carbon atom of 2 or 3, followed by lactonization to give the corresponding five- (4) or six-membered spiro-lactones (5) possessing cyclopropane rings in moderate to good yields.

Re-characterization of three conjugated linolenic acid isomers by GC–MS and NMR

Conjugated linolenic acids (CLN) refer to a group of octadecatrienoic acids with three conjugated double bonds. Minor positional and geometrical differences among CLN isomers make their separation and identification difficult. We have used GC–MS and NMR to study three common CLN isomers namely α-eleostearic acid, β-eleostearic acid and punicic acid, finding that some signals of olefinic carbon atoms in NMR spectra were mistakenly assigned in the literature. The present study was therefore undertaken to re-characterize the location of C C double bonds and assign the chemical signals of proton and carbon atoms using 1H NMR, 13C NMR, 1H– 1H two-dimensional correlation spectra ( 1H– 1H COSY) and 13C– 1H two-dimensional correlation spectra ( 13C– 1H COSY). The geometrical structure of double bonds in these three CLN isomers was identified using homonuclear decoupling technique.