Showing papers on "Double bond published in 1985"

Bond order and charge localization in nucleoside phosphorothioates

Abstract: In the recent literature on nucleoside phosphorothioate anions the structural formulas show a double bond between phosphorus and sulfur and a single bond between phosphorus and oxygen with a negative charge localized on oxygen However, a review of physical data on these compounds shows the reverse to be the case; that is, in phosphorothioate anions the P-S bond is a single bond with a negative charge localized on sulfur, while the P-O bond order for exocyclic and nonbridging oxygens is greater than 1, approaching 2 in O-alkyl phosphorothioate monoanions and O,O-dialkyl phosphorothioates The P-O bond orders in phosphorothioate dianions and trianions approach 1 1/2 and 1 1/3, respectively, owing to delocalization of negative charge among two or three oxygens These conclusions are based on bond lengths obtained from x-ray crystallographic data and electron diffraction, the magnitudes of the effects of 18O on the 31P-nuclear magnetic resonance chemical shifts of phosphorus in nucleoside [18O]phosphorothioates, the pH-dependence of 17O-NMR chemical shifts in [17O]phosphate and [17O]thiophosphate, the vibrational spectra of thiophosphate di- and trianions, and the pKa (dissociation constant) values for phosphoric and thiophosphoric acids

A study on the photochemical dimerization of coumarins in the solid state

Abstract: Solid-state photochemical behavior of 28 substituted coumarins has been investigated. Of these twelve underwent photodimerization and this is remarkable in light of the inertness of coumarin itself in the solid state. X-ray crystallographic investigation of eight coumarins was undertaken with the view of understanding the role of packing in the crystal on their solid-state reactivity. Important findings include the identification of acetoxy and chloro substituents as useful “crystal engineering” groups and the results pertaining to subtler aspects of topochemical postulates. X-ray crystal structure analyses of 7-chlorocoumarin and 7-methoxycoumarin reveal packing modes which are not commonly met. The former is arranged in a \beta type packing, the center-center distance between the reactive double bonds being 4.454 \AA, which lies beyond the so far accepted limit of 3.5-4.2 \AA. The reactive double bonds of 7-methoxycoumarin, on the other hand, are rotated by $65^O$ with respect to each other with the center-center distance between the double bonds being 3.83 \AA. Inspite of these unfavorable arrangements photodimerization of the above two coumarins in the solid state occurs through a topochemical process with large dimer yields. A careful analysis of the X-ray crystallographic resulta obtained from our investigations reveals that the two double bonds in the reactive crystals may be displaced with respect to each other both along the molecular plane as well as along the double bond axis. Thus the normally accepted dictums that in the photoreactive crystals the doube bonds should be within a distance of 4.2 \AA, and that they be parallel are no longer operational.

Über die Wechselwirkung zwischen Lithium-enolaten und sekundären Aminen in Lösung und im Kristall

Abstract: On the Interaction between Lithium Enolates and Secondary Amines in Solution and in the Crystal When lithium derivatives generated by lithium diisopropylamide (LDA) are quenched with a D+ source (large excess of ROD), there is frequently only partial deuterium incorporation (non-stoichiometric effect, Scheme 1). Experiments with tert-butyl 2-methylpropionate (1) and its deuterated derivative (2-D)-1 and LDA indicate that the lack of deuteration is not caused by an isotope effect (Scheme 2). A H-bonded complex between the amine (R2NH) and the Li-derivative was envisioned as being responsible for the observed effects. Some crystalline Li-enolate solvates with secondary amines were isolated, and gave rise to only partially deuterated products upon quenching with AcOD/CD3OD (Table 1). Enolates containing the Li-chelating diamine N,N,N′-trimethylethylenediamine (TriMEDA) turned out to be especially suitable for the isolation of single crystals. Thus, two X-ray crystal-structure analyses were undertaken to obtain detailed information about the geometry and bonding in such complexes. The structures of the dimeric N,N-dimethyl-propionamide lithium (Z)-enolate ([2 (Z)-4·2 TriMEDA]; R value 0,049, see Eqn. 2, Figs. 2, 4 and (5) and of the dimeric pinacolone lithium enolate ([2 6·2 TriMEDA]; R value 0,082, see Eqn. 3 and Figs. 3, and 6) were determined. In both centrosymmetric dimeric structures there is a Li-O-Li-O four-membered ring and a H-bridge between TriMEDA and the enolate moiety. In the case of the amide enolate (Z)-4·TriMEDA the bridge points from the amine N-atom to the pyramidalized, enamine-type N-atom of the enolate (N … N distance 3.173(1) A, H … N distance 2.21 (A). In the complex 6·TriMEDA of the ketone enolate there is a H-bridge pointing from the amine N-atom to the enolate double bond (N … Cterminal distance 3.45(1) A, H … Cterminal distance 2.62 A; see Table 3). The geometries of the TriMEDA-Li fragments in the two structures are compared with those of standard TMEDA-Li moieties (Table 2). The two structures are discussed and interpreted using the structure correlation principle; the intermolecular interactions seen in these complexes are considered as points on the reaction coordinates of conversions between the species involved. Thus, they resemble the approach of a secondary amine in the protonation of an enamine N-atom and of an enolate C-atom. At the same time, they represent the final stages of deprotonation of an enammonium ion and of a ketone. The NH … N bridge in 4 is in agreement with experimental observations and with calculations by Muller, indicating that enamines are kinetically protonated on the N-atom. From the pinacolone enolate structures which are now known, (a) possible transition states of deprotonation of carbonyl compounds by Li-amide bases (Figs. 7 and 8), (b) the hypothetical structure of a (i-Pr)2NH/ethyl tert-butyl ketone (E)-enolate (Fig. 8b and Fig. in Footnote 18), c) the approach of the two trigonal centers in an aldol-addition reaction, and the d) trajectory of electrophile attack on a double bond (Fig. 9) are deduced using simple molecular modeling without energy minimization. A comparison with and a discussion of the experimental and theoretical investigations about these same processes by Ireland, Corey, Dauben, Williard, and Houk are given. Finally, we believe that the H-bonding discovered in the crystal structures (Z)-4·TriMEDA and 6·TriMEDA is relevant to what Cram once called the ‘conducted-tour’ mechanism of base-catalyzed racemizations.

Permanganate ion oxidations. 15. Additional evidence for formation of soluble (colloidal) manganese dioxide during the permanganate ion oxidation of carbon-carbon double bonds in phosphate-buffered solutions

Abstract: Etude dans des solutions tampon de phosphate de l'oxydation par l'ion permanganate des anions des acides acrylique, methacrylique, aryl-3 acryliques, crotonique et methyl-3 butene-2oique

Surface-enhanced Raman spectroscopy as a probe of adsorbate-surface bonding: simple alkenes and alkynes adsorbed at gold electrodes

Abstract: : The interaction of various alkenes with gold electrodes has been studied using surface-enhanced Raman spectroscopy (SERS). Large decreases, from 70 to 140/cm, were observed in the C-C double bond and C triple bond C stretching frequencies upon adsorption which are attributed to adsorbate-surface bonding involving these groups. The potential dependence of these SERS frequencies suggests that the Pi yield s (sigma band) overlap is more prevalent than the d yields pi* (pi bond) interaction. Carbon-hydrogen stretching vibrations, nu(C-H), as well as other skeletal modes were also detected for the adsorbates; paraffinic, olefinic, and aromatic nu(C-H) modes could readily be distinguished although acetylenic nu(CH) modes were too weak to be detected. Generally, the most intense SERS bands relative to those in the bulk-phase spectra are associated with vibrations of the carbon-carbon double or triple bonds. Attempts to examine SERS of adsorbated acetylene were thwarted by a spontaneous surface reaction yielding a film of polyacetylene.

Anti-inflammatory/anti-allergic compounds

Abstract: Compounds of the formula: and salts thereof, wherein Ar 1 is a nitrogen, sulfur, oxygen heterocyclic ring or aromatic ring; Ar is a phenyl ring or a nitrogen, oxygen or sulfur heterocyclic ring; Ar and Ar 1 may be fully substituted or less than fully substituted with H, CH 3 , lower alkyl, aryl, aralkyl, halo, hydroxy, lower alkoxy, CF 3 , carboxy, alkylcarboxy, arylcarboxy, alkylcarbalkoxy, alkanoyl, formyl, oxo, nitrilo, amino, aminoalkyl, alkylamine, carboxamide, aryloxy, nitro, sulfonyl, sulfonamide, thio, or alkylthio; X = -O(CHR 1 ) n -, , -NR 2 (CHR 1 ) n -alkylene of up to 2 carbon atoms in the principal chain and up to a total of 4 carbon atoms, Z is an alkylene chain containing up to 10 carbon atoms in the principal chain and a total of up to 12 carbon atoms and from 0 to 2 double bonds and the said alkylene chain may be attached to Ar through an oxygen, sulfur or amino nitrogen atom, and when n'= 2 , one of the R substituents may be halogen on an omega carbon of the alkylene chain Z; when n'=1, R is a substituent attached to one of the carbon atoms of Z selected from the group consisting of =0, OR 3 , SR 3 , N(R 2 ) 2 and R,, -COR 4 and when n'=2 one R is previously defined and the additional R is a substituent attached to one of the carbon atoms of Z selected from the group consisting of =O, OR 3 , SR a , N(R 2 ) 2 , -COR 4 , lactone and halo; R 1 is H or CH 3 ; R 2 is H, lower alkyl, aryl or aralkyl; R 3 is H, lower alkyl, lower alkanoyl, aryl, aralkyl or substituted aryl in which the substituent is halo, lower alkyl or lower alkoxy; R 4 is OR 2 or N(R 2 ) 2 ; n = 0 or 1; n' = 1 to 7; and n" = 0, 1 or 2. 2. A compound of the formula: and salts thereof, wherein Ar 1 is quinolyl; Ar is a phenyl, pyridyl or quinolyl ring; X = -O(CHR 1 ) n -, -, NR 2 (CHR 1 ) n -, alkylene of up to 2 carbon atoms in the principal chain and up to a total of 4 carbon atoms,

Iron(I) chemical ionization and tandem mass spectrometry for locating double bonds

Abstract: Determination d'une methode de localisation des doubles et triples liaisons dans les alcenes, alcynes, dienes, acides gras, esters gras et acetates d'alcenyles

Effects of replacement of a double bond by a cyclopropane ring in phosphatidylethanolamines: a 2H NMR study of phase transitions and molecular organization.

Abstract: The thermotropic behavior and molecular properties of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and 1-palmitoyl-2-dihydrosterculoyl-sn-glycero-3-phosphoethanolamine (PDSPE) have been investigated by 2H NMR spectroscopy using samples selectively labeled at the 5'-, 9'-, 10'-, and 16'-positions of the sn-2 chains. Comparison with the corresponding phosphocholine analogues (POPC and PDSPC), obtained as intermediate synthetic products, was used to monitor the role of the polar head group. Replacement of the choline moiety by ethanolamine increased the gel to liquid-crystal transition temperature by 10-32 degrees C and led to a significantly higher ordering of the fatty acyl chains in the liquid-crystalline bilayer state. The lateral compression effect, due to the smaller area per polar head group in PE, results in a bilayer to hexagonal phase transition at elevated temperatures. The effects on both PC and PE due to replacement of the olefinic group by a cyclopropane unit are similar. A decrease in the temperature of the gel to liquid-crystal phase transition, Tc, is observed upon introduction of a cyclopropane ring; it goes from 26 degrees C in POPE to approximately 10 degrees C in PDSPE. In addition, a very significant broadening of the transition profile is observed. These observations are consistent with the poor packing ability of mixed saturated and cyclopropane-containing chains due to the bulky substituent effect. The temperature of the bilayer-hexagonal phase transition of PE samples was decreased by 15-20 degrees C on replacement of oleoyl chains by dihydrosterculoyl chains at the sn-2 position.(ABSTRACT TRUNCATED AT 250 WORDS)

Electronic structure of the phosphoryl and thiophosphoryl bonds

Abstract: .The pho~phoryl bond is presented as a. resonan~e hybrid between singly and triply bound structures. The types of electromcally excited states and a number of their potential surfaces can be understood within the confines of a singly bound model: However, a detailed analysis of the electronic distribution within the ground state shows significant contribution from the tnpl~ bound structure. In fact, increasing the electronegativity of the ligands at phosphorus increases the contribution of t~e tnp~y bound structure, so that the. PO bond order approaches that of a double bond. The thiophosphoryl bond may be VIewed m much the same manner but IS rather weaker and contains less multiple bond character than does the PO group. As noted in a recent paper,1 the phosphoryl group in phosphine oxide can be written in several ways, \ \=o' \ P-QI P=:QI /j 4 I -I

Infrared spectroscopic evidence for silicon-oxygen double bonds: silanone and the silanoic and silicic acid molecules

Abstract: Silanon, H2SiO, wird als Zwischenverbindung bei Reaktionen mit Organosiliciumverbindungen postuliert.

Epoxidation of natural rubber studied by nmr spectroscopy

Abstract: Epoxidation of natural rubber with peroxyacids in homogeneous solution (CHCl3, benzene) and in latex occurs without main chain fission or isomerization of the cis configuration. There are two possible modes of addition of oxygen to the double bond, which gives rise to diastereoisomers in dyad structures, as shown by the occurrence of splitting of 13C NMR resonances in 100% epoxidized rubber. In partially epoxidized rubber the 13C NMR resonances of the methylene carbon atoms have been fully assigned using pulse sequences and lanthanide shift reagents, in terms of triad sequences. Resonances in the olefinic region of the spectrum require assignment in terms of pentad sequences whereas those from the oxirane region are much more closely spaced and are assigned using triads. Intensity measurements on the methylene carbon NMR resonances show that the epoxidation reaction is a random process in both homogeneous solution and in latex particles.

Recent advances in double bond formation

Abstract: This review is presented in five sections dealing respectively with the Wittig and related reactions, sulfone chemistry, allylic rearrangements, acetylene chemistry and miscellaneous.

Crystal structure of dehydromonopetide, (Z)‐N‐acetyl‐α,β‐dehydrophenylalanine methylamide

Abstract: The crystal structure of (Z)-acetyl-α,β-dehydrophenylalanine methylamide (monoclinic Cc, a = 10.241(1), b = 15.252(1), c = 8.643(1) A, β = 120.98(1)°, Z = 4) has been solved by x-ray diffraction to an R-factor = 0.148, and compared to that of the homologous L-phenylalanine dervative. Molecules are intermolecularly hydrogen-bonded to four neighboring molecules in a three-dimensional network with alternating layers of interacting amide bonds and orthogonally arranged phenyl rings. The existence of the Cα = Cβ double bond results in a phenyl orientation that is forbidden for phenylananine (χ1 = −7,8°), and in shorter Cα − Cβ and Cβ − Cγ distances. The geometrical paramenters of the peptide backbone are not drastically modified by α,β-unsaturation. However, the N-Cα-C′ angle is increased by nearly 5°, and the dimensions, and therefore probably the electronic conjugation, of the N-terminal amide group to be affected by the occurrence of the vicinal Cα = Cβ double bond.

Effect of alkyl side chain variation on the electron-transfer activity of ubiquinone derivatives.

Abstract: The effect of the alkyl side chain of the ubiquinone molecule on the electron-transfer activity of ubiquinone in mitochondrial succinate-cytochrome c reductase is studied by using synthetic ubiquinone derivatives that possess the basic ubiquinone structure of 2,3-dimethoxy-5-methyl-1,4-benzoquinone with different alkyl side chains at the 6-position. The alkyl side chains vary in chain length, degree of saturation, and location of double bonds. When a ubiquinone derivative is used as an electron acceptor for succinate-ubiquinone reductase, an alkyl side chain of six carbons is needed to obtain the maximum activity. However, when it serves as an electron donor for ubiquinol-cytochrome c reductase or as a mediator in succinate-cytochrome c reductase, an alkyl side chain of 10 carbons gives maximal efficiency. Introduction of one or two isolated double bonds into the alkyl side chain of the ubiquinone molecule has little effect on electron-transfer activity. However, a conjugated double bond system in the alkyl side chain drastically reduces electron-transfer efficiency. The effect of the conjugated double bond system on the electron-transferring efficiency of ubiquinone depends on its location in the alkyl side chain. When location is far from the benzoquinone ring, the effect is minimal. These observations together with the results obtained from photoaffinity-labeling studies lead us to conclude that flexibility in the portion of the alkyl side chain immediately adjacent to the benzoquinone ring is required for the electron-transfer activity of ubiquinone.