Search results for " NMR spectroscopy"

Mirror energy differences in theA=31mirror nuclei,S31andP31, and their significance in electromagnetic spin-orbit splitting

2005

Excited states in $^{31}\mathrm{S}$ and $^{31}\mathrm{P}$ were populated in the $^{12}\mathrm{C}$($^{20}\mathrm{Ne}$,n) and $^{12}\mathrm{C}$($^{20}\mathrm{Ne}$,p) reactions, respectively, at a beam energy of 32 MeV. High spin states of positive and negative parity have been observed in $^{31}\mathrm{S}$ for the first time, and the yrast scheme of $^{31}\mathrm{P}$ has been extended. Large mirror energy differences between the first $9/{2}^{\ensuremath{-}}$ and $13/{2}^{\ensuremath{-}}$ states were observed, but only small differences for the first $7/{2}^{\ensuremath{-}}$ and $11/{2}^{\ensuremath{-}}$ levels. The significance of these observations is discussed in relation to the electromag…

NMR Study of Kraft Pulp Mill Waste and Natural Humic Substances

1988

High field proton NMR spectroscopy in DMSO-d6 solution is applied for structural analysis of main high molecular fractions of natural humus and waste lignin from kraft pulp mill. The spectra are similar in great part. Main differences appear in p-disubstituted benzene proton and -CH2 -CO-proton signals which are absent in spectrum of waste lignin obviously due to chlorination. A new observation of 51 Hz 1:1:1 triplet in both spectra is discussed.

Stabilization of the rhombohedral phase in LiZr2(PO4)3 by thermal quenching

1993

Abstract Two LiZr2(PO4)3 samples, which show rhombohedral and monoclinic symmetries, have been studied by powder XRD and MAS-NMR (31P and 7Li) techniques. In the monoclinic sample phosphorus occupies three crystallographic sites and lithium is preferentially placed in M2 environment. When the samples are subjected to successive heating-quenching treatments, the rhombohedral phase is not appreciably modified while the monoclinic phase is transformed into the rhombohedral one. In the quenched samples only one site for phosphorus has been detected and occupancy of lithium in the more symmetric M1 site is favoured. After the thermal treatments, when the samples are stored at room temperature fo…

Reversible complexation of ethylene by a silylene under ambient conditions.

2014

Treatment of toluene solutions of the silylenes Si(SArMe6)2 (ArMe6 = C6H3-2,6(C6H2-2,4,6-Me3)2, 1) or Si(SArPri4)2 (ArPri4 = C6H3-2,6(C6H3-2,6-Pri2)2, 2) with excess ethylene gas affords the siliranes (ArMe6S)2tiebar above startSiCH2tiebar above endCH2 (3) or (ArPri4S)2tiebar above startSiCH2tiebar above endCH2 (4). Silirane 4 evolves ethylene spontaneously at room temperature in toluene solution. A Van’t Hoff analysis by variable-temperature 1H NMR spectroscopy showed that ΔGassn = −24.9(2.5) kJ mol–1 for 4. A computational study of the reaction mechanism using a model silylene Si(SPh)2 (Ph = C6H5) was in harmony with the Van’t Hoff analysis, yielding ΔGassn = −24 kJ mol–1 and an activatio…

13C NMR of carbonyl compounds. 3. Structure and dynamics of protonated enones and dienones

1984

Abstract The unsaturated ketones 1 1 – 10 10 were protonated at low temperatures and studied by dynamic 13C NMR spectroscopy. Four interconverting stereoisomers were detected which differ in their conformation with respect to the CO and CC (enone) single bond.

A New Methodological Approach to Correlate Protective and Microscopic Properties by Soft X-ray Microscopy and Solid State NMR Spectroscopy: The Case …

2021

Hydrophobic treatment is one of the most important interventions usually carried out for the conservation of stone artefacts and monuments. The study here reported aims to answer a general question about how two polymers confer different protective performance. Two fluorinated-based polymer formulates applied on samples of Cusa’s stone confer a different level of water repellence and water vapour permeability. The observed protection action is here explained on the basis of chemico-physical interactions. The distribution of the polymer in the pore network was investigated using scanning electron microscopy and X-ray microscopy. The interactions between the stone substrate and the protective…

TEMPLATE-FREE AND ALKALI-FREE SYNTHESIZED SILICATES WITH MFI-STRUCTURE -A COMPARATIVE STUDY

1993

ABSTRACT Zeolites and gallosilicates with an MFI-structure which were crystallized from inorganic reaction systems and from alkali-free, tetrapropylammonlumbromide (TPABr) containing systems are compared. The strength, nature and distribution of the acidic sites were determined by FTIR-spectroscopy, TPD, electron microprobing, 29 si, 27 Al and 1 H MAS NMR spectroscopy. The influences of the different trivalent elements as well as the strength, type and distribution of the acidic sites on the catalytic performance of the different MFI-silicates are discussed.

Aromatic Bridged Bis-phenol A Derived Cyclophanes. Synthesis, Molecular Structure and Binding Properties Toward Quats

2003

Three novel polyoxyethylene bridged bis phenol A derived cyclophanes, {\rm 2 -- 4,} with additional aromatic units in the bridge to increase the number of cation–π interactions with guest cations, were synthesized and characterized by means of X-ray crystal structure determinations. The binding properties of these receptors toward tetramethylammonium (TMA), N-methylpyridinium (NMP), acetylcholine (ACh) and N-methylquinolinium (NMQ) salts were evaluated by means of 1H NMR spectroscopy and compared with those of the previously reported receptor 1.

Novel Tetramethoxy Resorcinarene Bis-Crown Ethers

2006

The synthesis and characterization of new tetramethoxy resorcinarene bis-crown ethers BC4 and BC5 are described. The complexation properties of the compounds toward alkali metal cations were studied by 1H NMR spectroscopy and X-ray crystallography, which revealed that BC5 can accommodate two cations simultaneously inside the crown pockets formed by the crown ether bridges and the resorcinarene skeleton. [reaction: see text].

1981

Polyamides 3 containing constant and definite numbers of oxyethylene units were prepared by condensation polymerization of suitable diamines and diesters, both of which containing oxyethylene units. The polymer structure was determined by IR and 1H NMR spectroscopy. Almost all polymers are crystals melting at ≈ 40°C and show a complexation ability towards alkalimetal cations. It was also found that diesters containing oxyethylene units show a higher condensation rate than alkylene diesters, which is explained by an inductive effect of the ether oxygene. However, no remarkable difference in the condensation rate was found between diamines containing oxyethylene units and the corresponding al…