Search results for " Spectroscopy"
showing 10 items of 6851 documents
Karplus-Type Dependence of Vicinal119Sn-13C and119Sn-1H Spin-Spin Couplings in Organotin(IV) Derivatives: A DFT Study
2009
The empirical Karplus-type dependence of (3)J((119)Sn,(13)C) and (3)J((119)Sn,(1)H) couplings in organotin(IV) derivatives has been computationally validated by DFT methods both at the nonrelativistic and scalar ZORA relativistic level. A preliminary calibration of the computational protocols, by comparing experimental and calculated couplings for a Set Of Suitable rigid molecules, revealed their high predictive power: in particular, relativistic results for (3)J((119)Sn,(13)C) have a mean absolute error of just above 2 Hz, over a range of values up to about 70 Hz. The latter protocol has then been used to study in detail the influence of substituents and multiple paths connecting the coupl…
COMMUNICATION. OBSERVATIONS ON THE 121-Sb MÖSSBAUER PARAMETERS OF ANTIMONY (III) COMPOUNDS FEATURING A PYRAMIDAL SbS3SKELETAL UNIT
1991
Abstract A linear correlation between the chemical isomer shift and the quadrupole coupling constant for a number of antimony tris-thiolates has been evidenced. This behaviour can be rationalized on considering a modulation of the s/p character of the lone pair of electrons from the influence of secondary bonds.
Mössbauer spectroscopic studies of clusters Mn2(CO)8[μ-Sn(hal)Mn(CO)5]2 (hal = Cl, Br) and related Mn and Re compounds
1977
Abstract In order to be acquainted with the nature of bonds at Sn involved in the title compounds, as well as to get information on the configuration of the strictly related derivatives I2Sn2Mn4(CO)18 and Cl2Sn2Re4(CO)18, the Mossbauer spectroscopic investigation reported in this paper has been carried out. The experimental parameters (isomer shifts, δ; nuclear quadrupole splittings, ΔE; for the bromide derivative only, the asymmetry parameter η and the sign of the nuclear quadrupole coupling constant e2qQ) have been discussed in connection with data concerning compounds with tin-transition metal bonds, mainly hal2Sn[Mn(CO)5]2 (hal = Cl, Br) and ClSn[Mn(CO)5]3. Rationalizations of ΔE and η …
"Through-space" nuclear spin-spin J(PP) coupling in tetraphosphine ferrocenyl derivatives: a (31)P NMR and X-ray structure correlation study for coor…
2004
Herein, we report on (31)P(31)P solution-phase "through-space" nuclear spin-spin coupling constants (J(PP)) from a novel family of organometallic tetraphosphine nickel and palladium complexes. These J(PP) constants were accurately determined through NMR iterative simulation based on the second-order spectra obtained for the compounds. The corresponding solid-state X-ray structures of the complexes were determined, and the "through-space" P.P distances are reported. Due to the blocked conformation of the species in solution, a qualitative and semiquantitative experimental correlation is obtained, which links the geometric parameters and the intensity of the corresponding P.P coupling constan…
Nuclear Spin Relaxation in Viscous Liquids: Relaxation Stretching of Single-Particle Probes
2021
Spin-lattice relaxation rates R1(ω,T), probed via high-field and field-cycling nuclear magnetic resonance (NMR), are used to test the validity of frequency-temperature superposition (FTS) for the reorientation dynamics in viscous liquids. For several liquids, FTS is found to apply so that master curves can be generated. The susceptibility spectra are highly similar to those obtained from depolarized light scattering (DLS) and reveal an excess wing. Where FTS works, two approaches are suggested to access the susceptibility: (i) a plot of deuteron R1(T) vs the spin-spin relaxation rate R2(T) and (ii) a plot of R1(T) vs an independently measured reference time τref(T). Using single-frequency s…
“Through-space” nuclear spin–spin couplings in ferrocenyl polyphosphanes and diphosphino cavitands: A new way of gathering structural information in …
2009
Abstract Nuclear magnetic resonance is an invaluable technique for investigating a variety of important issues ranging from the determination of molecular structure to therapeutic medical imaging. In this respect, the indirect nuclear spin–spin coupling involving common nuclei such as 1 H, 13 C or 31 P provides, via the J constant, conclusive data for compound characterization in solution. This electron-mediated nuclear spin coupling is usually regarded as being transmitted by covalently bonded magnetic atoms. However, several experimental and theoretical studies, first focused on constrained organofluorides, and more recently devoted to phosphane ligands highlighted the existence of very i…
1H NMR and IR spectra of methyl dichloropropanoates and butanoates
1981
Abstract Methyl dichloropropanoates and butanoates were synthesized and their 1H NMR and IR spectra were studied. Comparisons were made with the spectral characteristics of corresponding monochlorocompounds. Special attention was given to the elucidation of the characteristic spectral features associated with particular chlorine substitution patterns. The 1H NMR of erythro and threo methyl 2,3-dichlorobutanoates were analyzed using a computer program MAOCON, a modified LAOCOON 3 program. In the spectrum of the threo form the order of the chemical shifts of protons on asymmetric carbons seems to be opposite to that reported in earlier literature. Also vicinal coupling constants J23 were foun…
O Triclusters Revisited: Classical MD and Quantum Cluster Results for Glasses of Composition (Al2O3)2(SiO2).
2005
The (17)O NMR spectrum of CaAl(2)Si(2)O(8) glass shows two types of O sites that are not present in the crystalline material. One of these, with (17)O NMR parameters C(Q) = 2.3 MHz and delta = +20 ppm, has been assigned to a "tricluster" O, a local geometry in which the O is coordinated to three tetrahedrally coordinated atoms, either Al or Si. For crystalline CaAl(4)O(7), a tricluster site (with three Al linkages to O, i.e., OAl(3)) has been characterized experimentally, with a C(Q) of 2.5 MHz and a delta of about +40 ppm. Thus, a C(Q) value of 2.5 MHz or less seems to be a characteristic of such sites, although they may show a range of delta values. However, several different quantum chem…
O Triclusters Revisited: Classical MD and Quantum Cluster Results for Glasses of Composition (Al2O3)2(SiO2)
2006
The (17)O NMR spectrum of CaAl(2)Si(2)O(8) glass shows two types of O sites that are not present in the crystalline material. One of these, with (17)O NMR parameters C(Q) = 2.3 MHz and delta = +20 ppm, has been assigned to a "tricluster" O, a local geometry in which the O is coordinated to three tetrahedrally coordinated atoms, either Al or Si. For crystalline CaAl(4)O(7), a tricluster site (with three Al linkages to O, i.e., OAl(3)) has been characterized experimentally, with a C(Q) of 2.5 MHz and a delta of about +40 ppm. Thus, a C(Q) value of 2.5 MHz or less seems to be a characteristic of such sites, although they may show a range of delta values. However, several different quantum chem…
Conformation of the galactose ring adopted in solution and in crystalline form as determined by experimental and DFT 1H NMR and single-crystal X-ray …
2003
The solution-state conformations of various galactose derivatives were determined by comparison of the experimental (1)H-(1)H vicinal coupling constants to those calculated using density functional theory (DFT) at the B3LYP/cc-pVTZ//B3LYP/6-31G(d,p) level of theory. The agreement between the experimental and calculated vicinal coupling constants for 1,2:3,4-di-O-isopropylidene-alpha-d-galactopyranose was good, thereby confirming an (O)S(2) skew conformation for it and its derivatives on the basis of their similar observed couplings. Single-crystal X-ray analysis of 1,2:3,4-di-O-isopropylidene-6-O-(3,4,6-tri-O-acetyl-2-deoxy-2-N-phthalimido-beta-d-glucopyranosyl)-alpha-d-galactopyranose and …