Search results for "single bond"
showing 10 items of 66 documents
The electronic substituent influence on the thermally allowed electrocyclic interconversion cyclobutene/butadiene. A MNDO study
1984
The effects of donor/acceptor substitution on the conrotatory cyclobutene/butadiene interconversion have not yet been experimentally studied. MNDO Synchronous Transit/MINIMAX calculations for all possible combinations of NH2/NH3 + 3 groups at the fissile single bond reveal very large substituent effects on the opening reactions and reverse cyclisations. Diamino(1b/2b), diammonio-(1c/2c) and amino-ammonio-substitutions (1d/2d) change the activation energy of the reference ring opening reaction (1a →2a) from 49.9 kcal/mol to 34.7, 29.8 and 26.0 kcal/mol, respectively. This rate enhancement parallels the monotone shift of the transition state pathcoordinate towards the cyclobutenes. Relative t…
1-[(1-ethoxypropylidene)amino]-2-ethyl-4-(4-hydroxybenzyl)imidazol-5(4H)-one.
2012
The racemic title compound, C17H23N3O3, isolated from the reaction of L-(−)-tyrosine hydrazide with triethyl orthopropionate in the presence of a catalytic quantity ofp-toluenesulfonic acid (p-TsOH), crystallizes withZ′ = 1 in a centrosymmetric monoclinic unit cell. The molecule contains two planar fragments,viz.the benzene and imidazole rings, linked by two C—C single bonds. The dihedral angle between the two planes is 59.54 (5)° and the molecule adopts a synclinal conformation. The HOMA (harmonic oscillator model of aromaticity) index, calculated for the benzene ring, demonstrates no substantial interaction between the two π-electron delocalization regions in the molecule. In the crystal …
Conformational equilibrium in supramolecular chemistry: Dibutyltriuret case
2015
The association of substituted benzoates and naphthyridine dianions was used to study the complexation of dibutyltriuret. The title molecule is the simplest molecule able to form two intramolecular hydrogen bonds. The naphthyridine salt was used to break two intramolecular hydrogen bonds at a time while with the use of substituted benzoates the systematic approach to study association was achieved. Both, titrations and variable temperature measurements shed the light on the importance of conformational equilibrium and its influence on association in solution. Moreover, the associates were observed by mass spectrometry. The DFT-based computations for complexes and single bond rotational barr…
Über zinn-haltige heterocyclen
1983
Abstract The crystal structure of 2,2,6-trimethyl-1,3-dithia-6-aza-2-stannocane has been determined and refined to R = 0.043. The transannular 1,5-distance Sn ⋯ N = 256.6(6) pm exceeds the respective single bond by 49 pm. A comparison with analogous eight-membered rings exhibits a clear-cut correlation of such differences with angle deformations in the transition tetrahedron to trigonal-bipyramid. The axial distance SnC is 2 pm longer than the equatorial one.
Preparation and structural characterization of (Me(3)SiNSN)(2)Se, a new synthon for sulfur-selenium nitrides.
2002
The reaction of (Me(3)SiN)(2)S with SeCl(2) (2:1 ratio) in CH(2)Cl(2) at -70 degrees C provides a route to the novel mixed selenium-sulfur-nitrogen compound (Me(3)SiNSN)(2)Se (1). Crystals of 1 are monoclinic and belong the space group P2(1)/c, with a = 7.236(1) A, b = 19.260(4) A, c = 11.436(2) A, beta = 92.05(3) degrees, V = 1592.7(5) A(3), Z = 4, and T = -155(2) degrees C. The NSNSeNSN chain in 1 consists of Se-N single bonds (1.844(3) A) and S=N double bonds (1.521(3)-1.548(3) A) with syn and anti geometry at the N=S=N units. The N-Se-N bond angle is 91.8(1) degrees. The EI mass spectrum shows a molecular ion with good agreement between the observed and calculated isotopic distributions…
Bonding Trends in Lewis Acid Adducts of S 4 N 4 – X‐ray Structure of TeCl 4 ·S 4 N 4
2006
Tetrasulfur tetranitride and tellurium tetrachloride react in dichloromethane to form a 1:1 adduct TeCl4·S4N4 (1). The crystal structure of 1 shows that TeCl4 is bonded to the S4N4 ring through a Te–N linkage. As a consequence, the transannular S···S bonds in S4N4 are broken and the molecule assumes an open, monocyclic conformation. The Te–N bond of 2.16(1) A is slightly longer than the single bond. The S–N bonds span a range of 1.55(1)–1.67(1) A. The adduct 1 was also characterized by mass spectrometry and Raman spectroscopy. The bonding and spectroscopic properties of 1 are compared by DFT calculations at the B3PW91/(RLC ECP) level of theory with those of BF3·S4N4 (2), SO3·S4N4 (3), AsF5·…
Cs3UP2S8, a Coordination Polymer Containing the Unprecedented [U=S]2+Sulfidouranium(2+) Moiety
2013
Although terminal chalcogeno ligands are well known for the group 5 and 6 transition metals, they are highly unusual for the oxophilic group 4 metals and unknown so far for the lanthanides or actinides. Cs3UP2S8, is the first actinide compound containing a terminal M=S group. It was synthesized by reacting uranium metal, Cs2S, S, and P2S5 in a 4:1:8:3 ratio at 700 °C in an eutectic LiCl/CsCl mixture. The crystal structure was determined by single-crystal X-ray diffraction techniques. Cs3UP2S8 crystallizes in the rhombohedral space group R [a = 15.5217(8) A; c = 35.132(2) A, V = 8305.0(8) A3, Z = 18]. The crystal structure is based on a tetrahedral network type, wherein the uranium atoms are…
Muscarinic Properties of Compounds Related to Arecaidine Propargyl Ester
2011
A series of new analogues of the arecaidine propargyl ester (CAS 35516-99-5, APE, 1a) with alcohols consisting of 4 or 5 carbon atoms were investigated at muscarinic receptor subtypes. The muscarinic activity of the quaternary and tertiary salts of the APE-related compounds were assayed on the isolated guinea-pig ileum (M 3 receptor subtype) and guinea-pig left atria (M 2 receptor subtype) as well as on rabbit isolated vas deferens (M 1 receptor subtype). The structural variations made in the APE molecule, replacing the triple bond in the ester side chain with structures such as double bond, an allene moiety, a single bond, a cyclopropyl group or two triple bonds should alter the selectivit…
Effect of different adhesive strategies on the microtensile bond strength of dentin to indirect resin-based composite.
2020
Background To evaluate the microtensile bond strength of indirect resin composite bonded to dentin using five different adhesives strategies. Material and Methods Forty specimens (Solidex) were produced and randomly into five groups with different adhesives strategies: (G1)- Single Bond Universal + etch + silane + RelyX Ultimate, (G2)- Single Bond Universal + silane + RelyX Ultimate, (G3)- Single Bond Universal + etch + RelyX Ultimate, (G4)- Single Bond Universal + RelyX Ultimate, and (G5)-Scotchbond Multi-purpose + RelyX ARC. After cementation the specimens were stored in 100% humidity for 24hours at 37°C. The specimens were sectioned perpendicular to the adhesive interface to obtain beams…
Dentin bonding agent with improved bond strength to dentin through incorporation of sepiolite nanoparticles.
2017
Background The study aims to investigate the effect of incorporation of sepiolite nanoparticles on the microtensile bond strength of an experimental dentin bonding to the human dentin. Material and methods The sepiolite nanoparticles were incorporated into an experimental methacrylate-based dentin bonding system in concentrations of 0.0, 0.2, 1.0, 2.0, and 5.0 weight percents. The specimens were then ultrasonicated to finely disperse the nanoparticles in the adhesive matrix. The coronal enamel of 30 intact human premolars was cut to expose dentin. Having etched, rinsed, and blot dried the experimental bonding agents were applied to dentin surface. Adper Single Bond was used as control group…