scholarly journals Cluster-Cluster Potentials for the Carbon Nucleus

2020 ◽  
Vol 10 (04) ◽  
pp. 35-45
Author(s):  
K. A. Kharroube
Keyword(s):  
Carbon Nucleus

New Strategy of Synthesis of Peramivir Analogues as Potential Neuraminidase Inhibitors

Synthesis ◽  
2019 ◽  
Vol 52 (06) ◽  
pp. 933-941
Author(s):  
Roberta Bartolotta ◽  
Concetta La Rosa ◽  
Donatella Nava
Keyword(s):  
Cycloaddition Reaction ◽  
Nitrile Oxide ◽  
Hydroxyl Group ◽  
Dipolar Cycloaddition ◽  
Carbon Nucleus ◽  
Neuraminidase Inhibitors ◽  
Subsequent Reaction ◽  
New Strategy

Highly functionalised potential neuraminidase (NA) inhibitors, analogues of peramivir, were synthesised via a new and versatile method starting from a stereoselective 1,3-dipolar cycloaddition reaction between the nitrile oxide derived from 2-ethylbutanal and the commercially available and inexpensive cyclopentadiene and 1,3-cyclohexadiene, which afforded the isoxazolino-cyclopentene or cyclohexene intermediates, respectively. The subsequent reaction of the C=C bond in different conditions allowed the functionalisation of the five (or six) membered carbon nucleus. Further functionalised derivatives displaying an amino and a hydroxyl group were achieved via the final opening of the isoxazoline ring.

Non-Liouvillian carbon nucleus accumulation at the ITEP storage accelerator facility

JETP Letters ◽  
2003 ◽  
Vol 77 (3) ◽  
pp. 123-125 ◽  
Author(s):  
N. N. Alekseev ◽  
D. G. Koshkarev ◽  
B. Yu. Sharkov
Keyword(s):  
Carbon Nucleus ◽  
Accelerator Facility

A solid-state 13C NMR and theoretical investigation of carbonyl and thiocarbonyl carbon chemical shift tensors

1995 ◽  
Vol 73 (4) ◽  
pp. 604-613 ◽  
Author(s):  
Christopher W. Kirby ◽  
Michael D. Lumsden ◽  
Roderick E. Wasylishen
Keyword(s):  
Solid State ◽  
Chemical Shift ◽  
Ab Initio ◽  
Principal Axis ◽  
Comparative Investigation ◽  
Conclusive Evidence ◽  
Carbon Nucleus ◽  
Chemical Shift Tensors ◽  
Carbon Chemical Shift ◽  
C Nmr

The carbon chemical shift tensors of the carbonyl and thiocarbonyl groups of acetamide, thioacetamide, thioacetanilide, 4′-methoxyacetanilide, and 4′-methoxythioacetanilide have been experimentally determined using dipolar – chemical shift solid-state 13C NMR spectroscopy. The magnitudes of the three principal components of the carbon chemical shift tensors are found to exhibit marked variations between the carbonyl and thiocarbonyl functionalities. However, in contrast to the conclusions of an earlier comparative investigation involving benzophenone and thiobenzophenone, the orientations of the principal axis systems of these chemical shift tensors are found to be similar. These experimental results represent the first complete characterizations of the carbon chemical shift tensor in organic thiocarbonyls. The results of our ab initio GIAO and LORG calculations of carbon chemical shielding tensors in formaldehyde, thioformaldehyde, formamide, and thioformamide as well as in acetamide and thioacetamide are in qualitative agreement with experiment. The findings of the present investigation provide conclusive evidence that the well-known isotropic deshielding of the carbon nucleus in the C=S group relative to C=O is primarily attributable to the decreased energy associated with the σ ↔ π* excitation within the thiocarbonyl fragment. This result is in contrast with the conventional interpretation that the deshielding originates from a red shift in the C=S HOMO–UMO n → π* transition. Keywords: chemical shift tensors, solid-state 13C NMR, carbonyls, thiocarbonyls, ab initio calculations.

scholarly journals The theory of the stability of the benzene ring and related compounds

1934 ◽  
Vol 146 (856) ◽  
pp. 223-238 ◽  
Keyword(s):  
Benzene Ring ◽  
Accurate Solution ◽  
Great Length ◽  
Carbon Nucleus ◽  
Electron Pairs ◽  
Best Value ◽  
Single Ring ◽  
Ring Structures ◽  
The Stability ◽  
Related Compounds

There are two fairly distinct problems involved in a treatment of the stability of the benzene ring. The first is to explain why of all the single-ring structures C n H n , that of benzene ( n = 6) is by far the most stable. The second is to examine the different models proposed by the chemists for the benzene ring in the light of quantum mechanics and to show in fact that they are all represented with varying probabilities in the complete model. Attempts have been made at both problems, but only the second has been worked out satisfactorily. In the present paper we attempt a more accurate solution than has hitherto been given of the first problem. Before commencing this it is necessary to give a description of previous work, since otherwise it is very difficult to see what is already certain and what remains to be done. In a series of papers Hückel has discussed at great length both of the problems mentioned above, not only for the simple benzene ring, but also for many of its substitution products. He evaluates the energy of the plane ring compound in two ways, one of which virtually amounts to the method of generalized electron pairs and the other to that of molecular orbitals. The chief weakness in his theory is that he considers only what he calls the p r electrons, viz., the n 2 p -electrons whose wave functions are odd for reflection in the plane of the ring. As we shall show, the three remaining bonding electrons on each carbon nucleus have a most important influence on the best value of n . Nevertheless, Hückel's work is quite satisfactory as regards the resonance between the p r electrons.

THE NUCLEAR MAGNETIC RESONANCE SPECTRUM OF VINYLENE CARBONATE

1966 ◽  
Vol 44 (3) ◽  
pp. 321-326 ◽  
Author(s):  
K. A. McLauchlan ◽  
T. Schaefer
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nuclear Magnetic Resonance Spectrum ◽  
Resonance Spectrum ◽  
Double Resonance ◽  
Carbon Nucleus ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Carbonate Group ◽  
Vinylene Carbonate

The H and 13C spectra of vinylene carbonate have been studied by double-resonance techniques. It was found that J(13C—H) = ±220.15 ± 0.15 c/s, J(13C—C—H) = ±17.47 ± 0.12 c/s, and J(H—C—C′—H′) = ±1.47 ± 0.03 c/s. A long-range coupling of 9.26 ± 0.10 c/s was observed between the carbon nucleus of the carbonate group and the vinyl protons. The magnitudes and signs of the geminal 13C—C—H couplings are discussed in terms of the molecular orbital theory of Pople and Bothner-By.

C13 CHEMICAL SHIFTS IN ORGANIC CARBONYL GROUPS

1964 ◽  
Vol 42 (7) ◽  
pp. 1563-1576 ◽  
Author(s):  
J. B. Stothers ◽  
P. C. Lauterbur
Keyword(s):  
Chemical Shifts ◽  
Carbon Nucleus ◽  
Carbonyl Groups ◽  
Carbonyl Carbon ◽  
Resonance Position ◽  
Factors Affecting ◽  
Carbonyl Derivatives ◽  
Potential Applications ◽  
Major Factors

The results of a study of the resonance position of the carbonyl carbon nucleus in an extensive series of carbonyl derivatives are reported. A discussion of the major factors affecting the position of these carbon resonances is presented and some of the potential applications of these data to chemical problems are indicated.

Properties of atoms in molecules: nuclear magnetic shielding

1996 ◽  
Vol 74 (2) ◽  
pp. 185-200 ◽  
Author(s):  
T.A. Keith ◽  
R.F.W. Bader
Keyword(s):  
Magnetic Field ◽  
Current Density ◽  
Atoms In Molecules ◽  
Magnetic Shielding ◽  
Carbon Nucleus ◽  
Property A ◽  
Methyl Carbon ◽  
Atomic Property ◽  
Magnetization Density ◽  
Nuclear Magnetic

This paper analyzes the nuclear magnetic shielding tensors underlying the chemical shift in NMR spectroscopy in terms of the field generated at the nucleus by the current J(1)(r) induced by an external magnetic field. The magnetic field at nucleus [Formula: see text] resulting from an element of the induced current density at a distance [Formula: see text] is proportional to [Formula: see text] which defines the shielding density [Formula: see text] The magnetic shielding of a nucleus is fundamentally an atomic property, a feature brought to the fore by using the theory of atoms in molecules and the integration of [Formula: see text] over the individual atomic basins relates the shielding tensor [Formula: see text] to a sum of atomic contributions. The shielding of nucleus ** is primarily determined by the flow of current within the basin of atom [Formula: see text], a contribution that varies from the approximate diamagnetic limit, given by the atomic Lamb value for the atom in the molecule, to values that are greatly reduced by the presence of paramagnetic current flows associated with particular bonding effects. Whether the contribution of a neighbouring atom is shielding or deshielding is readily understood by relating the form of the current flow within its basin to the magnetization density. [Formula: see text]. A study of the currents induced in benzene shows that the extent to which a proton, bonded to a ring of atoms, is deshielded by the field exerted by its bonded neighbour provides a direct diagnostic test for a ring current and an accurate relative measure of its strength. The theory of atoms in molecules isolates transferable atomic properties and because of this ability one finds, in addition to the anticipated result that a given functional group contributes identical amounts to the isotropic shielding [Formula: see text] of a nucleus external to it through a series of molecules, the more remarkable result that the whole of the variation in [Formula: see text] can have its origin in the basin of atom [Formula: see text], the contribution from external groups remaining constant. For example, the external contribution to [Formula: see text] for a carbon nucleus in a normal hydrocarbon is independent of chain length and position of [Formula: see text] within the chain, the methyl group in ethane contributing the same shielding to a methyl carbon as does the butyl group in pentane. This constancy in external contributions to the shielding is also found for N, O and F nuclei in substituted, saturated hydrocarbons. Key words: NMR, magnetic shielding, current density, magnetic shielding density.

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