Search results for " molecule"
showing 10 items of 1523 documents
Electronic structure and energy decomposition analyses as a tool to interpret the redox potential ranking of naphtho-, biphenyl- and biphenylenequino…
2016
By calling on modelling approaches we have performed a comparative study on the redox properties of various naphtho-, biphenyl- and biphenylene-quinone isomers. These different compounds exhibit as a whole a redox potential range between 2.09 and 2.90 V vs. Li+/Li. A specific methodology was used to decrypt the interplay among isomerism, aromaticity and antiaromaticity modifications and the stabilization/destabilization effects due to other molecular components on this key electrochemical feature for electrode materials of batteries. In particular, energy decomposition analysis, within the Quantum Theory of Atoms in Molecules, along with the electron and electron spin population changes upo…
Glandulosides A-D, triterpene saponins from Acanthophyllum glandulosum.
2004
Four novel triterpenoid saponins, glandulosides A (1), B (2), C (3), and D (4), together with two known saponins (5 and 6) have been isolated from the roots of Acanthophyllum glandulosum. Their structures were elucidated using a combination of homo- and heteronuclear 2D NMR techniques (COSY, TOCSY, NOESY, HSQC, and HMBC) and by FABMS. The new compounds were characterized as 23-O-beta-D-galactopyranosylgypsogenic acid-28-O-beta-D-glucopyranosyl-(1-->3)-[beta-d-galactopyranosyl-(1-->6)]-beta-D-galactopyranoside (1), 3-O-beta-D-galactopyranosyl-(1-->2)-[beta-D-xylopyranosyl-(1-->3)]-beta-D-glucuronopyranosylgypsogenin-28-O-beta-D-xylopyranosyl-(1-->3)-beta-D-xylopyranosyl-(1-->4)-alpha-l-rhamn…
endo-Functionalized molecular tubes : selective encapsulation of neutral molecules in non-polar media
2016
Four endo-functionalized molecular tubes with urea/thiourea groups in the deep cavities have been synthesized, and their binding ability to neutral molecules studied. Very high binding affinity and selectivity have been achieved, which are rationalized by invoking the shape and electrostatic complementarity and dipole alignment.
Activation of the Cyano Group at Imidazole via Copper Stimulated Alcoholysis
2019
Reactions of 4,5-dicyano-1-methylimidazole with CuX2 (X = Cl, Br) in alcohol solvents (ethanol and methanol) resulted in the formation of Cu(II) carboximidate complexes [CuCl2(5- cyano-4-C(OEt)N-1-methylimidazole)(EtOH)] (1), [Cu2(µ
A study of the diels-alder reaction of 3-oxabicyclo[3.3.0]oct-1(5)-ene-2,4-dione with cyclopentadiene and some related dienes
1984
Abstract The reaction of 3-oxabicyclo[3.3.0]oct-l(5)ene-2,4-dione, 2, with cyclopentadiene, 3, 5,5-diethoxycyclopentadiene, 4, and 6,6-dimethylfulvene, 5, is studied. Reaction of 2 and 3 yields the expected endo-adduct, while reaction of 2 and 5 gives a mixture of the endo- and exo-adducts whose ratio is slightly dependent on the reaction conditions. Attractive electrostatic interactions in the transition state leading to the exo-adduct can explain the absence of endo stereoselectivity in the last reaction. Steric factors seem to be responsible for the absence of reaction between 2 and 4. The analysis of the 13C NMR spectra of these adducts and some derived compounds confirms the tentative …
Substrate-dependent fluorinations of highly functionalized cycloalkanes
2016
Abstract Substrate-dependent fluorinations of several highly functionalized cycloalkanes with multiple stereocentres were investigated. The synthetic transformations were based on selective functionalization of the ring C C bonds of the readily available bicyclic β-lactams by epoxidation and regioselective nucleophilic oxirane opening with azide or cyanide, followed by hydroxy–fluorine exchange with Deoxofluor. Depending on the substituents and their relative steric arrangement, the attempted fluorinations produced different types of substituted cycloalkanes. These selective, substrate-directed synthetic procedures and their presumed pathways towards interesting highly functionalized fluori…
Asymmetric synthesis of bicyclic amino acid derivatives by Aza-Diels-Alder reactions in aqueous solution
1991
Derivatives 7–10 and 13–16 of methyl and ethyl 2-azabicyclo[2.2.1]heptane-3-carboxylates are synthesized by Aza-Diels-Alder reactions of chiral iminium ions, formed in situ from glyoxylic acid and chiral amines, with cyclopentadiene. Whereas the heterodienophiles derived from phenylglycinol and esters of sterically more demanding amino acids fail to undergo asymmetric cycloadditions, with alanine methyl ester and (R)-1-phenylethylamine hydrochoride the cycloadducts are formed in yields of 15 and 52%, respectively, reaching de values of up to 90:10 for the exo isomers.
Intramolecular Nitrone Cycloaddition of α-(Trifluoromethyl)styrenes. Role of the CF3 Group in the Regioselectivity
2017
The intramolecular 1,3-dipolar cycloaddition of ortho-substituted 1,1,1-trifluoromethylstyrene-derived nitrones is described. Tricyclic fused isoxazolidines were obtained as major or exclusive products, in contrast to the case for nonfluorinated substrates, which rendered the bridged derivatives. This change in the regioselectivity was attributed to the electronic and, particularly, steric requirements of the trifluoromethyl group in comparison to the methyl group. It is worth mentioning that trifluoromethylstyrenes have been employed for the first time as dipolarophiles in a 1,3-dipolar intramolecular cycloaddition reaction, leading to the corresponding isoxazolidines bearing a quaternary …
Complexation of Small Molecules by Open-Ended Resorcarene Hosts
2002
[structure: see text] Sterically hindered tetraaminomethylated resorcarenes form inclusion complexes in CDCl(3) with acetonitrile and acetaldehyde, which are kinetically stable on the NMR time scale at 233 K.
Reactions of 1-isopropyl-3-methyl- and 2,3-dimethylindoles with triethyl orthoformate: New trisindolylmethanes
1987
Indoles 1 and 2 react with triethyl orthoformate under proton–catalyzed conditions to form trisindolylmethanes. The regioisomer distribution of the products is controlled by steric and electronic factors.