Search results for "Moiety"
showing 10 items of 621 documents
Borane reaction chemistry. Alkyne insertion reactions into boron-containing clusters. Products from the thermolysis of [6,9-(2-HC[triple bond]C-C5H4N…
2008
The stirring of [ortho-(HC[triple bond]C)-C(5)H(4)N] with [nido-B(10)H(14)] in benzene affords [6,9-{ortho-(HC[triple bond]C)-C(5)H(4)N}(2)-arachno-B(10)H(12)] 1 in 93% yield. In the solid state, 1 has an extended complex three-dimensional structure involving intramolecular dihydrogen bonding, which accounts for its low solubility. Thermolysis of 1 gives the known [1-(ortho-C(5)H(4)N)-1,2-closo-C(2)B(10)H(11)] 2 (13%), together with new [micro-5(N),6(C)-(NC(5)H(4)-ortho-CH(2))-nido-6-CB(9)H(10)] 3 (0.4%), [micro-7(C),8(N)-(NC(5)H(4)-ortho-CH(2))-nido-7-CB(10)H(11)] (0.4%) , 4 binuclear [endo-6'-(closo-1,2-C(2)B(10)H(10))-micro-(1(C),exo-6'(N))-(ortho-C(5)H(4)N)-micro-(exo-8'(C),exo-9'(N))-(…
The influence of CH bond polarization on the self-association of 2-acylaminopyrimidines by NH/CH···O/N interactions: XRD, NMR, DFT, and AIM study
2013
The single crystal structures of two 2-acylaminopyrimidines, where alkyl groups in acyl moiety are iso-propyl (1) and dichloromethyl (2), were solved by X-ray diffraction method. The strength of intermolecular hydrogen bonding interactions depends on the C–H bond polarization increased by exchanging two methyl groups by chlorine atoms in the adjacent substituent. The computational methods provide an additional insight into the intermolecular interactions and are utilized in explaining the differences in the observed crystal structures. The experimental and computational data together explain the differences in the formed aggregates and revealed that these simple substitutions cause crucial …
Identification and structural characterization of O-beta-ribosyl-(1"----2')-adenosine-5"-phosphate in yeast methionine initiator tRNA.
1990
We report in this paper on the complete structure determination of the modified nucleotide A*, now called Ar(p), that was previously identified in yeast methionine initiator tRNA as an isomeric form of O-ribosyl-adenosine bearing an additional phosphoryl-monoester group on its ribose2 moiety. By using the chemical procedure of periodate oxidation and subsequent beta-elimination with cyclohexylamine on mono- and dinucleotides containing Ar(p), we characterized the location of the phosphate group on the C-5" of the ribose2 moiety, and the linkage between the two riboses as a (1"----2')-glycosidic bond. Since the structural difference between phosphatase treated Ar(p) and authentic O-alpha-rib…
ChemInform Abstract: Calixcrowns : Synthesis and Properties
2009
The synthesis and properties of calix[n]crowns (n = 4–8), calix[n]biscrowns and their related compounds, resorcinarene crowns, have been discussed and reviewed. These macrocycles exhibit remarkable ionophoric properties toward alkali and alkaline earth metal cations, as well as, to tertiary amines. The selectivity and efficiency of calixcrowns in binding cations have been attributed to their structural features, which include substituent effects and size of the crown ether moiety and, conformation of the parent calixarene.
Glass-forming non-symmetric bis-styryl-DWK-type dyes for infra-red radiation amplification systems
2019
Abstract A series of D-π-A type organic dyes with bulky triphenylmethyl moiety containing 2,6-bis-(4-substituted)styryl-4H-pyran-4-ylidene donor (D) fragments and different electron acceptors (A) were synthesized and investigated, mostly for potential applications in organic solid-state lasers as infra-red (IR) radiation amplification medium. Dye glass transition temperature is above 99 °C with thermal stability in the region from 173 °C to 326 °C which was slightly influenced by the electron acceptor fragment attached to the 4H-pyrane ring in 4-position. Introducing substituents in 4-position within one of the styryl-fragments with stronger electron withdrawing properties decreased ASE exc…
A DFT study of the mechanism of NHC catalysed annulation reactions involving α,β-unsaturated acyl azoliums and β-naphthol.
2016
The mechanism of NHC catalysed annulation reactions involving an α,β-unsaturated acyl azolium and β-naphthol has been studied using DFT methods at the MPWB1K/6-311G(d,p) level in toluene. For the C-C bond formation step, which corresponds to the rate- and stereo-determining step of this NHC catalysed reaction, the two competitive addition modes, i.e. the 1,2- and the 1,4-additions, have been studied. In toluene, acyl azolium forms an ion pair (IP) with the counterion chloride anion. Interestingly, β-naphthol forms a hydrogen bond with the chloride anion of IP, increasing the nucleophilic character of β-naphthol and the electrophilic character of the acyl azolium moiety. For the first time, …
Asymmetric Synthesis of Spirobenzazepinones with Atroposelectivity and Spiro-1,2-Diazepinones by NHC-Catalyzed [3+4] Annulation Reactions
2016
A strategy for the NHC-catalyzed asymmetric synthesis of spirobenzazepinones, spiro-1,2-diazepinones, and spiro-1,2-oxazepinones has been developed via [3+4]-cycloaddition reactions of isatin-derived enals (3C component) with in-situ-generated aza-o-quinone methides, azoalkenes, and nitrosoalkenes (4atom components). The [3+4] annulation strategy leads to the seven-membered target spiro heterocycles bearing an oxindole moiety in high yields and excellent enantioselectivities with a wide variety of substrates. Notably, the benzazepinone synthesis is atroposelective and an all-carbon spiro stereocenter is generated.
A novel synthesis of polymers with anthracene and dihydroanthracene subunits in the main chain
1993
A new polycondensation method to connect redox-active and chromophoric subunits by forming a C-C bond and leading to a polyhydrocarbon is described. 1,ω-bis(9,10-Dihydro-9-anthry)alkanes with various alkylene spacers can be deprotonated by butyllithium to afford a monoanion in each dihydroanthracene moiety. Alkylation with dielectrophiles such as dibromoalkanes yields soluble polymers with dihydroanthracene units in the main chain. The reaction proceeds regioselectively in the 9,10-position. Aromatization generates a polymer with anthracene units. The molecular weights are determined by GPC up to Mn = 10 000. To prove the structure and to calibrate the GPC, suitable model compounds were syn…
Selective access to either a doubly boron-doped tetrabenzopentacene or an oxadiborepin from the same precursor
2019
Depending on the solvent, a brominated arylborane gave the multiple helicene B2-TBPA (pyridine) or the oxadiborepin ODBE (THF) after intramolecular Yamamoto coupling.
The Catalytic Effect of Fluoroalcohol Mixtures Depends on Domain Formation
2017
In the present contribution, we investigated catalytically active mixtures of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and aqueous H2O2 by molecular dynamics simulations. It is clearly observable that the HFIP molecule strongly binds to the H2O2, which is necessary for the desired catalytic reaction to occur. Upon the addition of the substrate cyclooctene to the solution, this interaction is enhanced, which suggests that the catalytic activity is increased by the presence of the hydrocarbon. We could clearly observe the microheterogeneous structure of the mixture, which is the result of the separation of the hydroxyl groups, water, and H2O2 from the fluorinated alkyl moiety in the form of l…