Location Of Double Bonds Research Articles

Double Bonds in Fused Hexacyclic Systems

If a hexacyclic graph, G, represents a benzenoid, a perfect matching corresponds to the location of double bonds (pi-bonds). We present an algorithm for counting the number of configurations of double bonds for various benzenoids.

Novel diterpenoids and hydrocarbons in the Dufour gland of the ectoparasitoid Habrobracon hebetor (Say) (Hymenoptera: Braconidae).

Chemical constituents contained in the Dufour gland of the ectoparasitoid Habrobracon hebetor (Say) (Hymenoptera: Braconidae) were characterized. Three terpenes, beta-springene, a homo-beta-springene, and a homo-geranyllinalool constitute approximately 37% of the gland components, with the remaining 63% all being hydrocarbons. The hydrocarbons consist of a homologous series of n-alkanes (n-C21 to n-C31), a trace amount of 3-methyl C23, a homologous series of internally methyl-branched alkanes (11-methyl C23 to 13-methyl C35), one dimethylalkane (13,17-dimethyl C33), a homologous series of monoenes (C(25:1) to C(37:1)) with the double bonds located at Delta9, Delta13 and Delta15 for alkenes of carbon number 25 to 31 and at Delta13 and Delta15 for carbon numbers 33 to 37 and three homologous dienes in very low amounts with carbon numbers of 31, 32, and 33. The terpenoid and hydrocarbon composition of the Dufour gland was similar in virgin and mated females. However, in contrast to the hydrocarbons, the amount of beta-springene and homo-geranyllinalool increased significantly with time after adult emergence from the cocoon. Although many hydrocarbons in the Dufour gland are the same as those on the cuticle of this species [Howard and Baker, Arch. Insect Biochem. Physiol. 53:1-18 (2003)], substantial differences also occur. Of particular note is the chain length of alkenes and location of the double bonds: cuticular alkenes have a chain length of C23 to C29 and double bond locations at Delta5, Delta7, and Delta9, whereas the Dufour gland alkenes contains a greater range of carbon numbers and have no Delta5 or Delta7 alkenes. The Dufour gland contains only one of the long-chain dimethylalkanes found on the cuticle. Also, no terpenoids are found on the cuticle, and the Dufour gland contains none of the secondary wax esters that are major components on the cuticle. GC-MS analysis of lipids carried in the hemolymph of H. hebetor indicated that all hydrocarbons found on both the cuticle and in the Dufour gland are present, as are some of the wax esters. However, none of the terpenoids were detected in the hemolymph. This suggests that the hydrocarbons are synthesized in other tissues or cells, probably by oenocytes, and differentially partitioned between the cuticle and the Dufour gland. The terpenoids are most likely synthesized within the Dufour gland. Analysis of surface lipids from eggs laid within 18 h indicated that no diterpenoids were present. Rather, the lipids present on the eggs were n-alkanes, monomethylalkanes, alkenes, and secondary alcohol wax esters. This composition did not reflect that of the Dufour gland, hence eggs are not being coated with Dufour gland components during oviposition.

DFT Investigation of Alkoxide Formation from Olefins in H-ZSM-5

We present a density functional theory (DFT) study of propene, 1-hexene, and 3-hexene protonation over representative H-ZSM-5 clusters to give covalent alkoxide intermediates. The influence of cluster size, olefin carbon number, olefin conformation, proton siting, aluminum siting, and bonding configuration (primary vs secondary) of the alkoxide intermediate was analyzed. We found the formation of a physisorbed π-complex involving the olefin double bond and the acidic proton to be relatively independent of olefin structure and site geometry. However, we show that the proton-transfer process for formation of the covalent alkoxide intermediate involves a carbenium-ion-like transition state, with an activation energy that is (1) dependent on the protonation site of the olefin and (2) relatively independent of the carbon number and double bond location of the olefin. Accessibility of the alkoxide oxygen site in the cavity was observed to play a significant role in the stability of the alkoxy species. We find t...

Syntheses and Structures of Tris-(1,2-Benzosemiquinone DIimine) Complexes of Rhenium(IV)

Reactions of trans-[ReO2(py)4Cl] and cis-[ReO2I(PPh3)2] with 2,3-diaminophenol (H2dab-OH) and 1,2-diaminobenzene (H2dab), respectively, in ethanol under aerobic conditions led to the corresponding isolation of [Re(sbqdi-OH)3]Cl (1) and [Re(sbqdi)3]I (2). Crystallographic data show that the ligand sbqdi represents the monoanionic N,N-coordinated π-radical form of the 1,2-benzosemiquinone diimine of H2dab. The ligands in Complex 1 clearly show semiquinoid character; e.g., the two C-N and two Re-N bondlengths differ considerably. In 2, the phenyl rings display typical quinoid distortions with two localized double bonds, and the C-N bondlengths are short, approaching double bonds. Rhenium is formally in the +IV oxidation state.

A procedure for preparing oxazolines of highly unsaturated fatty acids to determine double bond positions by mass spectrometry

A convenient, mild, reliable method has been developed for preparing oxazolines of fatty acids and for using these derivatives to determine double bond locations in long-chain polyunsaturated and polyconjugated fatty acids. Fatty acyl mixed anhydrides are prepared using isobutylchloroformate and then converted to their ethanolamides by treatment with ethanolamine. Ethanolamides are subsequently cyclized to the corresponding oxazolines in >or=85% yields by treatment with trifluoroacetic anhydride under mild conditions (>50 degrees for 30-60 min). This general protocol can also be used to synthesize 4,4-dimethyloxazoline and benzoxazole derivatives of fatty acids. Gas chromatography-mass spectrometry of oxazoline derivatives of fatty acids yields prominent ions diagnostic of the structures of the parent fatty acids and, in the case of unsaturated fatty acids, indicating the positions of the double bonds. The utility of the method is illustrated with several fatty acids, including the conjugated 4E,6E,8E,10E,13Z,16Z,19Z-docosaheptaenoic acid.

Theory of the effect of unsaturation on the main-chain transition.

We calculate the temperature of the main transition of lipids as a function of chain length for saturated lipids, and as a function of location of a cis double bond for lipids with one or two monounsaturated chains. We employ an extension of Marcelja's self-consistent field method which contains only two interaction parameters, and include many more chain orientations. Agreement with experiment on both the variation with chain length and with location of the double bond is satisfactory.

New particle formation during <font face="Symbol" >a</font>- and <font face="Symbol" >b</font>-pinene oxidation by O<sub>3</sub>, OH and NO<sub>3</sub>, and the influence of water vapour: particle size distribution studies

Abstract. New particle formation during the oxidation of a- and b-pinene (C10H16) by ozone, OH and NO3 was studied by measuring the particle size distributions with a scanning mobility particle sizer (TSI 3936). The results indicate a drastically higher nucleation potential of the ozonolysis than in the reaction with either OH or NO3. On the contrary, the contribution of the individual oxidation reactions to form new aerosol volume was found to depend on the location of the carbon double bond to be oxidised: for the endocyclic a-pinene reactions the ozonolysis contributed mostly to the aerosol volume yield, whereas for the exocyclic b-pinene reactions the oxidation by O3, OH and NO3 yielded a similar aerosol volume. In a second part of this study the influence of water vapour on the nucleation in all three possible oxidation routes was examined. The observations revealed only an effect of water vapour during the ozonolysis reactions.

Oxophlorin and metallooxophlorin radicals--DFT studies.

A flexible oxophlorin macrocycle, which allows the location of labile hydrogen atoms alternatively at the pyrrole nitrogen, oxygen, or meso-carbon atoms, has been studied by density functional theory (DFT). DFT calculations were carried out on oxophlorin 1, 5-hydroxyporphyrin 2, and two isomers of oxophlorin 3 and 4 (the proton added at the tetrahedral C(15) or the C(10) meso-carbon, respectively). The oxophlorin-hydroxyporphyrin structural changes are appropriately reflected by the significant changes of the meso carbon-oxygen bond lengths, which are in the limits of typical C=O and C-O distances. The rearrangement that creates the iso-oxophlorin macrocycle 3 (4) results in near tetrahedral geometry around the C(15) (C(10)) carbon atom, with the C(14)-C(15) and C(15)-C(16) (C(9)-C(10) and C(10)-C(11)) bond lengths corresponding to a single C-C bond. 5-Hydroxyporphyrin 2 is aromatic and has a bond pattern resembling that of regular porphyrin. In 1, 3, and 4, a localization of single and double bonds was seen, which agrees with the nonaromatic nature of oxophlorin, or isooxophlorin. The relative stability decreases in the order: 2 (0) > 3 (4.85) > 1 (5.11) > 4 (10.04) > 3-cis (12.89) (the number in parentheses is the relative energy, in kcal mol-1). The energy difference between the NH-cis and NH-trans tautomers, which is 8.04 kcal mol-1 for 3, results from a destabilizing NH-NH cis-interaction. DFT calculations were performed on the oxophlorin dianion radical (OP.)2- and a series of metallooxophlorin radicals ([(OP.)LiI]-, [(OP.)ZnII], [(OP.)GaIII]+, and (OP.)GaIIIF, in order to assess their electronic structures. Typically, the largest atomic spin density was found at the C(10) (C(20)) and C(15) meso positions, with the spin density at C(15) being twice as large as that at C(10). The spin density at the C(5) atom is negligible. A large spin density was found at the O(5) oxygen atom. The amount of spin density at the meso positions decreased as the cationic charge increased. When considering the absolute values of the spin densities, the opposite trend was observed at the pyrrolic carbon atoms. The spin density at the nucleus (Fermi contact terms) has also been analyzed. The spin distributions of iron oxophlorins determined by NMR were attributed to an oxophlorin radical electronic structure. The calculated spin density maps accounted for the essential NMR spectroscopic features of important intermediates in the heme degradation process--iron oxophlorin complexes. The DFT calculations reproduced the following spectroscopic patterns: a) |delta H(15)|>|delta H(10)|>>|delta (beta-H)|, b) a sign alteration of the contact shifts for identical substituents located on the same pyrrole ring.

Location of functional groups in mycobacterial meromycolate chains; the recognition of new structural principles in mycolic acids.

Mycobacterial alpha-, methoxy- and keto-mycolic acid methyl esters were separated by argentation chromatography into mycolates with no double bond, with one trans double bond or with one cis double bond. Meromycolic acids were prepared from each methyl mycolate fraction by pyrolysis, followed by silver oxide oxidation, and analysed by high-energy collision-induced dissociation/fast atom bombardment MS to reveal the exact locations of the functional groups within the meromycolate chain. The locations of cis and trans double bonds, cis and trans cyclopropane rings, methoxy and keto groups, and methyl branches within the meromycolate chain were determined from their characteristic fragment ion profiles, and the structures of the meromycolic acids, including those with three functional groups extracted from Mycobacterium tuberculosis H37Ra, Mycobacterium bovis BCG and Mycobacterium microti, were established. Meromycolic acids with one cis double bond were structurally closely related to those with one cis cyclopropane ring, whereas the meromycolic acids with one trans cyclopropane ring were closely related to the corresponding meromycolic acids with one cis cyclopropane ring. A close relationship between methoxy- and keto-meromycolic acids was also implied. The relationship between the meromycolic acids with a trans double bond and the other meromycolic acids was not clearly revealed, and they did not appear to be immediate substrates for trans cyclopropanation.

Novel marine flagellate fatty acid: structural elucidation by GC-MS analysis of DMOX derivatives and DMDS adducts.

In situ biodegradation experiments of marine particles were performed in deep Atlantic waters. Lipid changes were associated with the colonization of the decaying detritus by marine flagellates smaller than 10 microm in size. Fatty acid methyl esters (FAMEs) of these flagellates showed high proportion of a FAME with a molecular weight (MW) of 320. Its structure could not be unambiguously resolved by retention times on gas chromatography runs using polar and nonpolar columns, nor by routine gas chromatography coupled to mass spectrometry (GC-MS). Complementary GC-MS analysis of two types of derivatives was performed to fully elucidate the structure of this novel acid. GC-MS analysis of 4,4-dimethyloxazoline (DMOX) derivative of the compound enabled localization of a double bond in position Delta17, whereas other double bond locations could not be unambiguously located by spectrum interpretation. DMDS addition on the flagellate biomarker produced monocyclic triadducts. Fragment suites corresponding to gradual losses of thiomethyl substituents indicated the presence of a five-membered thioether cycle, located on the methyl side of the derivative. Fragment suites produced by cleavage of C linked to sulfured substituents revealed various possible structures. However, interpretation of the spectra in relation with the fragmentation of the DMOX derivative yielded a convergent identification of the flagellate biomarker, as a non-methylene-interrupted C20:3Delta7,13,17 FAME.

The ozonolysis of ortho-xylene and its relevance to the history of the benzene problem

Using B3LYP density functional theory in conjunction with the 6-311++G** basis set, the relative rates of the initial rate-determining attack of ozone upon the carbon—carbon bonds of o-xylene are found to be 4,5- [Formula: see text] 3,4- > 2,3- > 1,2-. With the assumption that the final products glyoxal (G), methylglyoxal (M), and dimethylglyoxal (D) are determined by the site of the initial attack, and taking statistical factors into account, the ratio G:M:D is calculated to be 3:2:1. This is close to the value found experimentally, and identical to the result predicted by the contention that two nearly equivalent Kekulé–Pauling valence bond (resonance) structures of o-xylene exist and each localized carbon—carbon double bond of these structures is oxidized at the same rate. Although Frontier Molecular Orbital theory also predicts a 3:2:1 ratio of G:M:D, this theory incorrectly predicts that the initial attack of ozone will take place at the 1,2- and 4,5- bonds, with 1,2-attack slightly preferred. These results are discussed in relation to a recent historical analysis of the benzene problem, and it is concluded that since the products of ozonolysis of o-xylene are determined by the relative energies of the transition states leading to the four possible primary ozonides, these transition states should be the focus of theory.Key words: Kekulé structure, resonance, frontier orbital theory, density functional theory, kinetics.

Endoplasmic oleoyl-PC desaturase references the second double bond

The regiospecificity for the gene product of fad2, 1 1 We will employ the convention of using fad2 for the gene and oleoyl-PC desaturase or FAD2 for the gene product. This permits us to avoid describing the enzyme as a Δ 12 desaturase, or an ω-6 desaturase. The latter designations involve an assertion about the substrate specificity no longer tenable based on this work. PC is the abbreviation for phosphatidylcholine, the most important phospholipid substrate for this activity. GLC is gas-liquid chromatography. GC/MS spectroscopy is separation by capillary gas chromatography with mass spectral, electron-impact detection. the microsomal oleoyl-PC desaturase from higher plants, differs from some previous suggestions. Rather than only referencing the carboxyl group (a Δ 12 desaturase) or the methyl terminus (an ω-6 desaturase), this desaturase locates the second double bond in its substrates by first referencing the existing double bond. This specificity was demonstrated for the oleoyl-PC desaturase cDNA from the developing seeds of peanut ( Arachis hypogaea L) expressed in yeast ( Saccharomyces cerevisae). The expressed enzyme was capable of desaturating monounsaturated fatty acyl groups in membrane lipids. Endogenous palmitoleate was desaturated to cis, cis 9,12 hexadecadienoate (9( Z)12( Z)C16:2), endogenous oleate to linoleate (9( Z)12( Z) octadecadienoate), and cis 10-nonadecenoate (provided as a supplement in the growth medium) to 10( Z)13( Z)C19:2. The rule, Δ x+3 where x=9 is the double bond location in the substrate, best describes the consistent placement of the second double bond in the above monounsaturated substrates for the oleoyl-PC desaturase of higher plants.

NMR and Molecular Mechanics Studies on Configurational Isomerism and Conformational Equilibrium of Chiral Cyclohexenones

Chiral diastereomers of 2-isopropyl-5-methyl-6-(4-phenyl)benzylcyclohex-2-enone and their isomer 2-(4-phenylbenzyl)-3-methyl-6-isopropylcyclohex-2-enone, which are products of an acid-catalyzed intramolecular rearrangement of 3R,6R-2-(4-phenylbenzylidene)-3-methyl-6-isopropylcyclohexanone, were investigated to show that conformational analysis by molecular mechanics and 1H NMR spectroscopy permits an integrated solution of three structural problems: double bond location in an aliphatic ring for isomeric products; determination of the stereochemical configuration for the two diastereomers; evaluation of the conformational equilibrium between the diastereomers. Based on the results of calculations, this is achieved by estimating the configuration- and conformation-sensitive proton spin–spin coupling constants of the cyclohexenone ring for alternative structures and correlating them with 1H NMR data.

Rearrangement products of some 1R,4R-2-arylidene-p-menthan-3-ones in acidic media, their structures, and conformational analysis

1R,4R-2-(4-Phenylbenzylidene)-p-menthan-3-one in acidic media undergoes rearrangement with migration of the exocyclic double bond to the cyclohexane ring to form three 2-(4-phenylbenzyl) derivatives ofp-menthen-3-ones. The reaction products differ in the location of the endocyclic double bond (Δ1 or Δ4) and in the configuration of the new chiral C(2) center in the resultingp-menth-4-en-3-ones. The configurations of the 1R,2R- and 1R,2S-2-(4-phenylbenzyl)-p-menth-4-en-3-ones were established based on analysis of their1H NMR spectra in combination with calculations by molecular mechanics. The molecular conformations of these compounds as well as of some racemic 2-benzyl-p-menth-1-en-3-one derivatives were studied.

Two-Photon Fluorescence Excitation Spectrum of 1,6-Methano-[10]annulene

The two-photon fluorescence excitation spectrum of 1,6-methano-[10]annulene has been measured in fluid solution at room temperature between 25 000 and 40 000 cm-1 and in rigid solution at 77 and 15 K between 25 000 and 28 000 cm-1. The two-photon polarization ratios of both spectra have been determined. Spectral assignments have been made on the basis of two-photon polarization data, ab initio calculations, and comparison with one-photon data. The four excited states below 5 eV have been identified. Calculated one- and two-photon allowed intensities are in good agreement with results derived from the alternant hydrocarbon theory. The S0 → S1 two-photon intensity is mainly vibronically induced by b1 modes. The most active b1 vibration, the “Kekule”-type mode responsible for double bond localization in 1,6-methano-[10]annulene, shifts to ≈1540 cm-1 in S1 from the ground state 1355 cm-1 value. Applying two-photon polarization results to 1,6-methano-[10]annulene (C2v symmetry), the tensor elements of the strongest totally symmetric S0 → S1 (B1 × b1 × a1) transition have been estimated.

Di(2-pyridyl)-Amides and -Phosphides: Syntheses, Reactivity, Structures, Raman-Experiments and Calculations

The 2-pyridyl containing compounds (2-Py)2NH 1, (2-Py)2PH 2, Me2Al(2-Py)2N 3, Me2Al(2-Py)2P 4, Et2Al(2-Py)2N 5, Et2Al(2-Py)2P 6 and Et2Al(2-Py)2NAlEt37 have been synthesized and analyzed by solid state structure determination, FT-Raman spectroscopy and theoretical calculations in order to elucidate the charge density distribution. All di(2-pyridyl) amides and -phosphides coordinate the R2Al+ fragment via both ring nitrogen atoms, but the Lewis basicity of the central two-coordinated nitrogen atom in 5 is high enough to coordinate a second equivalent AlEt3 to form the Lewis acid base adduct Et2Al(2-Py)2NAlEt37. Several density functionals (BLYP, B3LYP, BPW91) have been examined in relation to various basis sets (6-31G, 6-31+G, 6-31G(d), 6-31+G(d)). This computational tool facilitates the unambiguous assignment of the Raman ring vibration frequencies. The shift to higher wavenumbers proceeding from the parent di(2-pyridyl)amine 1 and di(2-pyridyl)-phosphane 2 to the metal complexes 3 and 4 indicates partial double bond localization in the ring positions 3 and 5. This effect is more pronounced in the di(2-pyridyl)amide complexes than in the phosphide. Due to the higher electronegativity of the central nitrogen atom in 3, 5 and 7 compared to the bridging two-coordinated phosphorus atom in 4 and 6 the di(2-pyridyl)amide is the harder Lewis base. In the phosphides nearly all charge density couples into the rings leaving the central phosphorus atom only attractive for soft metals.

Structures and stabilities of C60(OH)4 and C60(OH)6 fullerenols

The quantum chemical investigation of C60(OH)4 and C60(OH)6 isomers have been carried out at the MNDO, AM1 and PM3 semiempirical molecular orbital levels. The relative energies of these fullerenol isomers have been calculated. For C60(OH)4 fullerenol, cis-1 isomer obtained exclusively from 1,2-additions to the adjacent 6,6 ring fusions is the lowest energy structure. For C60(OH)6, the most energetically preferred structure results from 1,2- and 1,4-addition to a cyclohexatriene in the carbon cage, which places two double bonds into 6,5 ring fusions. This result suggests that the localization of double bonds into 6,5 ring fusion is not necessarily unfavorable. The most likely structures of C60(SO4)n (n=1–6) were found out, and the most probable structures of fullerenols C60(OH)2n (n=1–6) synthesized by hydrolysis of these precursors were generated, via reaction mechanism considerations. Since there are many different methods to synthesize fullerenols, the experimentally obtained fullerenols are not expected to be necessarily the most energetically preferred structures, the considerations of the reaction mechanism or kinetic factors should be more important.

Growth of Escherichia coli on Medium Containing Glycine Increases Transformation Efficiency

a flophemesyl derivative. In the latter spectrum, an allylic cleavage between the first two double bonds is reflected by the ion at m/z 392, and allylic and vinylic leavages between the second and third double bonds re reflected by ions at m/z 432 and 420. These data ield useful information about double-bond location n USFAs (8), and structurally informative fragment ons in these spectra are produced by cleavage of onds remote from the charge site on the flophemesyl ster moiety. In conclusion, the present method is described in hich the compounds of saturated and monoor polynsaturated FAs are derivatized to their respective ophemesyl esters. The flophemesyl derivatives are eadily prepared, have excellent chromatographic roperties, and in complex mixtures, can distinguish etween the saturation and the degree of unsaturation. lso, concerning the identification of SFAs in several atrices, it is an especially advantageous method for etection and characterization. Because the M-15 ion s the most intense, the use of these derivatives faciliates the measurement of the molecular weight of trace mounts of unknown acids with much greater confience than is possible when using other derivatives.

Mass spectrometry of the 4,4-dimethyloxazoline derivatives of isomeric octadecenoates (monoenes)

Although 4,4-dimethyloxazoline (DMOX) derivatives of fatty acids have been widely used for structural analysis of fatty acids by mass spectrometry, spectra of relatively few authentic standards have been published. Confusion can result when double bonds are located near either end of the molecule, and errors have been promulgated in the literature. Mass spectra of DMOX derivatives of the complete series of isomeric octadecenoates are described. Even when spectra are not easily interpreted mechanistically in terms of the double bond location, they usually give distinctive fingerprints.

Mass spectrometry of the 4,4-dimethyloxazoline derivatives of isomeric octadecenoates (monoenes)

Although 4,4-dimethyloxazoline (DMOX) derivatives of fatty acids have been widely used for structural analysis of fatty acids by mass spectrometry, spectra of relatively few authentic standards have been published. Confusion can result when double bonds are located near either end of the molecule, and errors have been promulgated in the literature. Mass spectra of DMOX derivatives of the complete series of isomeric octadecenoates are described. Even when spectra are not easily interpreted mechanistically in terms of the double bond location, they usually give distinctive fingerprints.