Search results for "Carbon-13 NMR"
showing 10 items of 262 documents
Ferrocene-Containing Multifunctional Polyethers: Monomer Sequence Monitoring via Quantitative 13C NMR Spectroscopy in Bulk
2014
Ferrocenyl glycidyl ether (fcGE) and allyl glycidyl ether (AGE) are copolymerized via living anionic ring-opening polymerization to generate polyfunctional copolymers with molecular weights up to 40 300 g/mol and low molecular weight dispersities (Mw/Mn < 1.18). Copolymerizations were carried out in bulk at 100 °C and unexpectedly found to proceed without any isomerization of the allyl double bonds. The copolymerization behavior of fcGE and AGE was monitored by in situ quantitative 13C NMR kinetic measurements in bulk, evidencing the formation of random copolymers under these conditions, showing no gradient of comonomer incorporation. The redox-active behavior of the copolymers and homopoly…
Poly(carbonate) copolymers with a tailored number of hydroxyl groups from glycidyl ethers and CO2
2014
Functional poly(carbonate)s with multiple hydroxyl functionalities have been prepared by copolymerization of carbon dioxide (CO2) with glycidyl methyl ether (GME) and benzyl glycidyl ether (BGE) in various ratios, using a diethylzinc–pyrogallol catalyst system. Subsequent catalytic hydrogenation was employed for removal of the benzyl protecting groups at the polymer backbone. A series of copolymers with varying comonomer fractions from 0 to 100% was obtained. The copolymers possessed a broad range of molecular weights from 9000 to 30 000 g mol−1 and showed polydispersities Mw/Mn between 2.4 and 3.6. The materials were characterized via1H and 13C NMR, SEC and differential scanning calorimetr…
The anionic copolymerization of 5-(N,N-diisopropylamino)isoprene with styrene
1995
The anionic copolymerization of 5-(N,N-diisopropylamino)isoprene (N,N-diisopropyl-2-vinylallylamine) and styrene initiated with alkyllithium compounds is studied. Copolymers obtained from different compositions are characterized by size-exclusion chromatography (SEC), differential scanning calorimetry and by 1 H NMR and 13 C NMR spectroscopy. Under these conditions the dialkylaminoisoprene, similar to butadiene and isoprene, is more reactive than styrene and is incorporated faster into the polymer backbone. The incomplete conversion of the monomers has been attributed to the formation of intra-or intermolecular complexes between the Li + counterion at the chain end and amino groups. Because…
NMR and Quantum-Chemical Study on the Structure of Ester Enolate−Aluminum Alkyl Complexes as Models of the Active Center in the Anionic Polymerizatio…
1999
6Li and 13C NMR on ethyl α-lithioisobutyrate (EiBLi) and quantum-chemical (DFT) calculations on methyl α-lithioisobutyrate (MiBLi) were used to elucidate the structure of the active center in the anionic polymerization of methacrylates in the presence of triethylaluminum (AlEt3) in toluene. This study reveals ester enolate/aluminum alkyl complexes with different degrees of association, (MiBLi·AlEt3)n (n = 1, 2, 4), and different stoichiometries, MiBLi·xAlEt3 (x = 1, 2). In the presence of methyl pivalate (MPiv), which is taken as a model compound for the monomer and polymer, complexes such as (MiBLi·MPiv·AlEt3)n (n = 1, 2) are formed. These complexes can dissociate into MiBLi·2AlEt3 and MPi…
Effect of ramp size and sample spinning speed on CPMAS 13C NMR spectra of soil organic matter
2011
Abstract Cross polarization (CP) magic angle spinning (MAS) 13C NMR spectroscopy is a solid state NMR technique widely applied to study the chemical composition of natural organic matter. In high magnetic fields (>7 T), fast sample spinning is required in order to reduce the influence of spinning sidebands underlying other chemical shift regions. As the spinning speed increases, the Hartmann–Hahn matching profiles break down into a series of narrow matching bands. In order to account for this instability variable amplitude cross polarization techniques (e.g. VACP, ramp-CP) have been developed. In the present study, we experimentally verified the stability of the Hartmann–Hahn condition unde…
O-Alkylation of a lignite humic acid by phase-transfer catalysis
2006
A mild phase-transfer catalytic reaction has been conducted to O-alkylate the acidic functions of a lignite humic acid (HA), using tetrabutylammonium hydroxide as the phase-transfer catalyst. The HA acidic functional groups were made to react, in tetrahydrofuran, by nucleophilic substitution with several alkyl halides-methyl iodide, and ethyl, propyl, and butyl, and benzyl bromide. The occurrence of the O-alkylation reaction was assessed by elemental analysis and 1H NMR, CPMAS 13C NMR, and FTIR spectroscopy. Bonding of alkyl groups increased the carbon and hydrogen content and the H/C ratios of all the humic reaction products. Increased nitrogen in the reaction products suggested incomplete…
13C NMR study of aromatic ring-substituted (E)-3-phenylpropenals and (2E,4E)-5-phenylpenta-2,4-dienals
1990
13C and 1H chemical shifts together with C,H and H,H coupling constants are presented for (E)-3-phenylpropenal, (2E,4E)-5-phenylpenta-2,4-dienal and their o-OCH3- and o-, m- and p-NO2-substituted derivatives. The SCSs calculated for the aldehyde chains show similar effects on the ring carbons, except in the para position where the shorter chain causes a 3.3 ppm deshielding and the longer chain a 1.0 ppm shielding effect. This shift difference is reflected in all the ring-substituted derivatives of the two series of aldehydes, but not in the one-bond C,H coupling constants. The effect of aromatic ring substitution on 2J(C,CHO) seems to be mainly inductive in origin. The importance of the str…
1H,13C,17O and19F NMR spectroscopic study of isomeric ring-substituted monofluoro-(E)-3-phenylpropenals
1993
Isomeric ring substituted monofluoro-(E)-3-phenylpropenals (cinnamaldehydes) were synthesized in order to provide, with the NMR-active 19F nucleus, an insight into the influence of substituents and the transmission of electronic effects between the aromatic ring and the side-chain. Their 1H, 13C and 17O NMR chemical shifts and their nJ(H,H), nJ(H,F), nJ(C,H) and nJ(C,F) values were determined. Generally, the nJ(C,F) coupling constants correlate with the length of the coupling route and thus simplify the assignments of the 13C NMR spectra. Only the side-chain carbons C-2 and C-3 in the ortho-substituted compounds showed an exception to this rule. Many long-range nJ(H,F) (n = 4–7) values were…
Effective complexation of psychotropic phenethylammonium salts from a disodium dipyrazolate salt of macrocyclic structure
2002
The equilibrium stability constants (Ks) of ammonium pyrazolate complexes [L2−]2RN(R′)H2+ (3, R′ = H and 4, R′ = Me) formed from a macrocyclic disodium dipyrazolate salt 2[L2−] 2Na+ and ammonium salts (RNH3+X− or RN(Me)H2+X−) of psychotropic drugs and neurotransmitter catecholamines have been evaluated by electrochemical methods in DMSO solution. The resulting Ks values demonstrate that, except for (±)-amphetamine, the complexes formed by lipophilic primary [mescaline, (+)-amphetamine, (±)-p-methoxyamphetamine (PMA), (±)-3,4-methylenedioxyamphetamine (MDA)] and secondary [(±)-methamphetamine, (+)-methamphetamine and (±)-3,4-methylenedioxymethamphetamine (MDMA ‘ecstasy’)] phenethylamines are…
Synthesis of ruthenium(II) compounds with ortho-oxypyridinate ligands (hp). Crystal structure characterization of [Ru(η6-p-CH3C6H4CH(CH3)2)Cl(hp)]
1988
Abstract The reaction of [Ru(η6-p-cymene)Cl2]2 (p-cymene = p-CH3C6H4CH(CH3)2) with Nahp in THF yields [Ru(η6]-p-cymene)Cl(hp)] (1). The crystal structure of (1) has been determined by X-ray methods. (1) crystallizes in the space group Pbca, with a = 16.629(2), b = 10.201(3), c = 17.752(2) A. The compound contains one coordinated arene group, one chlorine and one hp group in a chelating coordination mode. The reaction of (1) with Aghp yields [Ru(η6-p-cymene)(hp)2] (2). The 13C NMR spectrum at - 70°C is consistent with a structure Ru(η6-p-cymene)(η2-hp)(η1-hp). At room temperature a rapid interconvertion between the two hp ligands occurs according to the observed 1H and 13C NMR spectra.