RESUMO
[structure: see text] An X-ray crystallographic study of unique hydrogen-bonded supramolecular solid-state networks comprised of a tetraarylboronic acid resorcinarene is described. When 1 is recrystallized from 9:1 MeOH:EtOH, partial esterification takes place to give compound 2, the corresponding half methyl ester, which forms an infinite two-dimensional array. Each molecule participates in 12 hydrogen bonds with other macrocycles. These hydrogen bonds are both B-OH- - - OH (phenolic) and OH (phenolic)- - -OH (phenolic).
Assuntos
Ácidos Borônicos/química , Resorcinóis/química , Cristalografia por Raios X , Ligação de Hidrogênio , Indicadores e Reagentes , Modelos Moleculares , Conformação MolecularRESUMO
The furocoumarin 1,2-dihydro-2-(1,2-dihydroxyprop-2-yl)-8H-furo[2,3-h]benzopyran-8-one crystallizes from methanol-water as the monohydrate C(14)H(14)O(5).H(2)O. Both chiral centers have the S configuration. Both OH groups and both H atoms of the water molecule form intermolecular hydrogen bonds with O.O distances in the range 2.7686 (18)-2.8717 (18) A.
RESUMO
The reaction of 5,5-bis(trimethylstannyl)cyclopentadiene with CpZrCl3 (Cp = eta 5-C5H5) affords the monostannylated metallocene complex (eta 5-Me3SnC5H4)CpZrCl2 (1), accompanied by variable amounts of (eta 5-ClMe2SnC5H4)CpZrCl2 (2). The complex (1) reacts with BCl3 or with ICl to afford 2 (Sn-CH3 cleavage), but with HCl, Cp2ZrCl2 is obtained instead (Sn-Cp cleavage). Depending on the reaction conditions, treatment of either 1 or 2 with BBr3 affords (eta 5-BrMe2SnC5H4)CpZrBr2 (3) or (eta 5-Br2MeSnC5H4)CpZrBr2 (4). The reaction of 1 with excess I2 affords the iodostannylated complex (eta 5-IMe2SnC5H4)CpZrCl2 (5). Two of the complexes (2.2C6H5CH3 and 4.THF) are crystallographically characterized. The adduct 4.THF has a distorted trigonal bipyramidal geometry about tin with a long O-Sn distance of 2.655 A. We find overall that Me3Sn substituents undergo electrophilic halodemethylation much more readily than corresponding Me3Si substituents, whereas the reactivities of the halostannylated complexes toward nucleophiles such as airborne moisture are much lower than those of their halosilylated counterparts.
RESUMO
The first Rh complex with an eta(4)-coordinated rac-et,ph-P4 ligand [et,ph-P4 = (Et2PCH2CH2)(Ph)PCH2P(Ph)(CH2CH2PEt2)] has been synthesized by reacting [Rh(nbd)2]BF4 with meso- or rac-et,ph-P4 in dichloromethane. The reaction occurs fairly rapidly at room temperature to form [rac-RhCl2(eta(4)-et,ph-P4)](+) in high yields, regardless of whether one starts with mixed or even pure meso-et,ph-P4 ligand. This unusual and highly selective metal assisted isomerization of the meso-et,ph-P4 ligand to its rac-et,ph-P4 disastereomer will be discussed.
RESUMO
Two polymorphs of the title compound, (4R,5R,6R,7R)-4,7-bis(hydroxymethyl)-1,3-dioxepane-5,6-diol, C(7)H(14)O(6), both have Z' = 2 at 100 K, and differ in their hydrogen-bonding patterns. The sodium iodide complex, NaI.C(7)H(14)O(6), is isomorphous with the NaCl complex, and has the mannitol, cation and anion all lying on twofold axes. The dioxepane rings of all three molecules are in the twist-chair conformation.
RESUMO
The title triterpene, D-friedoolean-14-en-3 beta-yl acetate, C32H52O2, was isolated from dichloromethane extracts of the roots of common ragweed Ambrosia artemisiifolia. The skeleton contains five fused six-membered rings with an average Csp3-Csp3 bond distance of 1.549 (6) A and one double bond of length 1.348 (6) A. The D and E rings are cis-fused. The compound also contains a beta-oriented acetate group with a C-O distance 1.461 (5) A.
Assuntos
Ácido Oleanólico/análogos & derivados , Raízes de Plantas/química , Triterpenos/química , Cristalografia por Raios X , Modelos Moleculares , Conformação Molecular , Ácido Oleanólico/química , Extratos Vegetais/químicaRESUMO
The carboxy group of 2-methyl-N-[(2-nitrophenyl)sulfonyl]alanine, C(10)H(12)N(2)O(6)S, forms centrosymmetric hydrogen-bonded dimers with an O.O distance of 2.629 (2) A and an intramolecular N-H. O(nitro) hydrogen bond N.O distance of 2.823 (2) A. 1-[(2-Nitrophenyl)sulfonylamino]cyclohexanecarboxylic acid, C(13)H(16)N(2)O(6)S, has Z' = 2 and forms similar interactions.
Assuntos
Alanina/análogos & derivados , Benzamidas/química , Ácidos Cicloexanocarboxílicos/química , Peptídeos/química , Alanina/química , Cristalografia por Raios X , Estrutura MolecularRESUMO
Chiral discrimination of enantiomers of 2-methyl-4-(2-oxo-2,3,3a,8b-tetrahydro-4H-indeno[1,2b]furan-3-yl-iden emethoxy)but-2-en-4-olide (commonly referred to as GR 24) by three polymeric chiral surfactants (PCS) is studied by use of chiral polymeric surfactant capillary electrophoresis (CPSCE). The CPSCE results indicate that the optical configurations of valine residues on the PCS backbone affect chiral resolution and elution order of GR24 stereoisomers. The L- and D-forms of poly(sodium N-undecanoyl valinate) provide baseline separation of all four enantiomers while the DL-form separates diastereomers of GR 24 (1). A model is presented rationalizing the migration behavior and chiral resolution of 1 in CPSCE. The actual configuration of the stereogenic centers of GR 24 and 3-[(2,5-dihydro-3-methyl-2-oxo-5-furanyl)oxo]-methylene-3,3a,6,6a-tetrah ydro-2H-cyclopenta[b]furan-2-one (GR 7) is established by a concerted application of high-resolution nuclear magnetic resonance spectroscopy and X-ray crystallography.