scholarly journals A permutation approach to the assignment of the configuration to diastereomeric tetrads by comparison of experimental and ab initio calculated differences in NMR data

2017 ◽  
Vol 13 ◽  
pp. 2478-2485 ◽  
Author(s):  
Przemysław J Boratyński
Keyword(s):  
Chemical Shift ◽  
Ab Initio ◽  
Nmr Data ◽  
Experimental Chemical Shift ◽  
C Nmr ◽  
Chemical Shift Deviations

Scoring permutations of experimental chemical shift deviations and DFT/GIAO calculated deviations of isotropic shieldings for sets of four diastereomers can help to assign their relative configurations. This method was exercised on a set of diastereomeric Cinchona alkaloid derivatives, where 13C NMR data always identified the proper configuration. The presented approach is also an attempt to quantify the assignment by exclusion.

15N and 13C nuclear magnetic resonance of deoxydinucleotide monophosphates. II. Protonation of the homo dimers deoxycytidylyl-(3′,5′)-deoxycytidine, thymidylyl-(3′,5′)-thymidine, and deoxyadenylyl-(3′,5′)-deoxyadenosine in dimethyl sulfoxide

1990 ◽  
Vol 68 (11) ◽  
pp. 2033-2038 ◽  
Author(s):  
Giovanna Barbarella ◽  
Massimo Luigi Capobianco ◽  
Luisa Tondelli ◽  
Vitaliano Tugnoli
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Dimethyl Sulfoxide ◽  
Phosphate Group ◽  
Nmr Data ◽  
13C Nuclear Magnetic Resonance ◽  
C Nmr ◽  
Nuclear Magnetic

The preferential protonation sites of the homo dimers deoxycytidylyl-(3′,5′)-deoxycytidine, thymidylyl-(3′,5′)-thymidine, and deoxyadenylyl-(3′,5′)-deoxyadenosine were established by nitrogen-15 and carbon-13 NMR in dimethyl sulfoxide, in the presence of varying amounts of CF3COOH. The nitrogen-15 NMR data show that in d(CpC) the capability of the two N3 nitrogens to accept the proton is slightly different. In d(TpT) and d(ApA) the protonation of the phosphate group leads to significant variations of the chemical shift of the carbons adjacent to phosphorus. Keywords: deoxydinucleotides, protonation, 15N and 13C NMR.

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.

13C-NMR chemische Verschiebung phenylsubstituierter polycyclischer Kohlenwasserstoffe / 13C-NMR Chemical Shift of Phenylsubstituted Polycyclic Hydrocarbons

1979 ◽  
Vol 34 (11) ◽  
pp. 1334-1343 ◽  
Author(s):  
W. Storek ◽  
J. Sauer ◽  
R. Stößer
Keyword(s):  
Chemical Shift ◽  
13C Nmr ◽  
Nmr Spectra ◽  
Ring Current ◽  
Current Effect ◽  
Nmr Data ◽  
Ring Current Effect ◽  
Anisotropic Contribution ◽  
Chemische Verschiebung ◽  
C Nmr

13C-NMR spectra of tetracene, rubrene, 1,3,5-tri-, penta-, and hexaphenylbenzene are reported. The discussion also includes the already known 13C-NMR data for diphenyl, 9,10-diphenyl-, 9,10-dibenzyl-, and 9,10-dimethyl-anthracene [1] as well as toluene. On the basis of CNDO/2 calculations different influences (diamagnetic and paramagnetic term, anisotropic contribution, ring current effect, geometry) on the chemical shift are analyzed for diphenyl and within the row benzene through tetracene

Modeling Substituent-Dependence of the Twist and Shielding in a Series of 4-Substituted N-(4-Nitrobenzylidene)anilines

2004 ◽  
Vol 69 (8) ◽  
pp. 1566-1576 ◽  
Author(s):  
Vladimír Proks ◽  
Miroslav Holík
Keyword(s):  
Chemical Shift ◽  
Ab Initio ◽  
Density Functional ◽  
Ring Current ◽  
Functional Theory ◽  
H Nmr ◽  
Current Contribution ◽  
Monosubstituted Benzenes ◽  
Experimental Chemical Shift

A series of 15 4-substituted N-(4-nitrobenzylidene)anilines was synthesized and studied by 1H NMR spectroscopy. Their ab initio calculated geometries and the shielding as expressed by aromatic ring currents were used in correlation analysis. The geometries were fully optimized using density functional theory B3LYP/6-311G** approaches. For the determination of the ring current contribution to the shielding of azomethine hydrogens Hα was used direct ab initio calculation of the chemical shielding in a model system. Experimental chemical shift values free of these contributions were successfully correlated with increments ap of chemical shift for monosubstituted benzenes. In the same manner, the contribution of the anisotropy of C=N double bond to Hm hydrogen were calculated and values of the Hm chemical shift free of this contribution were successfully correlated with increments of chemical shift am.

Carbon-13 nuclear magnetic resonance spectra of organic sulfur compounds. Substituent chemical shift (s.c.s.) effects in the 4-thiazoline-2-thione series

1976 ◽  
Vol 54 (10) ◽  
pp. 1660-1664 ◽  
Author(s):  
I. W. J. Still ◽  
N. Plavac ◽  
D. M. McKinnon ◽  
M. S. Chauhan
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Sulfur Compounds ◽  
Organic Sulfur ◽  
Organic Sulfur Compounds ◽  
Nmr Data ◽  
Nuclear Magnetic Resonance Spectra ◽  
C Nmr ◽  
Magnetic Resonance Spectra

13C nmr data have been obtained for a series of 4-thiazoline-2-thiones. Substituent chemical shift (s.c.s.) effects for methyl and phenyl substitution have been collated and are discussed in comparison with s.c.s. effects in other heterocyclic systems. Some attempt has also been made to compare our data with those reported previously for the thiazoles and for some thiones in the isothiazole series.

scholarly journals Configurational Study of Diastereoisomeric Royleanone Diterpenoids From Salvia concolor

2019 ◽  
Vol 14 (7) ◽  
pp. 1934578X1986265
Author(s):  
Mónica Díaz-Fernández ◽  
María I. Salazar ◽  
Pedro Joseph-Nathan ◽  
Eleuterio Burgueño-Tapia
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Absolute Configuration ◽  
Vibrational Circular Dichroism ◽  
Chemical Shift Assignments ◽  
Aerial Parts ◽  
Nmr Data ◽  
Nmr Chemical Shift Assignments ◽  
C Nmr

The known diterpenoids horminone (1) and taxoquinone (2) as a mixture, and pure 6,7-dehydroroyleanone (7) were isolated from the aerial parts of not yet studied Salvia concolor Lamb. Although 1 and 2 are known, the 1H Nuclear Magnetic Resonance (NMR) data of their acetyl derivatives 4 to 6 are only partially described. Moreover, the 13C NMR data assignments for 4 and 6 show some inconsistencies and reveal better agreement with those we obtained for diastereoisomeric 3 and 5. Since stereochemical aspects were in doubt, it was considered as mandatory to unambiguously determine the absolute configuration of 3 to 6 using vibrational circular dichroism spectroscopy, which then allowed the complete 1H and 13C NMR chemical shift assignments of 4 to 6.

scholarly journals Use of13C-NMR as complementar identification tool in essential oil analysis

1997 ◽  
Vol 13 (4) ◽  
pp. 265-273 ◽  
Author(s):  
José Wilson Alencar ◽  
Maria Goretti de Vasconcelos Silva ◽  
Maria Iracema Lacerda Machado ◽  
Afrânio Aragão Craveiro ◽  
Francisco José de Abreu Matos ◽  
...  
Keyword(s):  
Chemical Shift ◽  
Carbon Atom ◽  
Essential Oil ◽  
Chemical Shifts ◽  
Chemical Constituents ◽  
Structural Features ◽  
Oil Analysis ◽  
Nmr Data ◽  
C Nmr ◽  
Identification Tool

A program using13C-NMR data was developed to improve GC/MS identifications of chemical constituents in essential oils. Compiled data uses 2290 and 2370 chemical shifts of 229 monoterpenes and 158 sesquiterpenes, respectively, stored into two reference libraries. Each carbon atom was codified using rules that correlates its chemical shift with structural features of the carbon hybridization and vicinity.

Synthesis, characterization and structural computational investigation of novel Zn(II) phthalocyanines containing peripheral anthracene moieties

2019 ◽  
Vol 23 (07n08) ◽  
pp. 943-959
Author(s):  
Nilgün Kabay ◽  
Burak Doğan Bozer ◽  
Aslı Öztürk Kiraz ◽  
Yasemin Baygu ◽  
İzzet Kara ◽  
...  
Keyword(s):  
Chemical Shift ◽  
Ground State ◽  
Atomic Orbital ◽  
Molecular Geometry ◽  
Basis Set ◽  
Spectroscopic Techniques ◽  
Computational Investigation ◽  
Ft Ir ◽  
Experimental Chemical Shift ◽  
C Nmr

New zinc(II) phthalocyanines (ZnPc-I and ZnPc-II) containing four peripheral anthracene pendant groups were synthesized by cyclotetramerization of (E)-4-(3-(4-((anthracen-9-yl-methylene)amino)phenoxy)propoxy)phthalonitrile and 4-(3-(4-((anthracen-9-ylmethyl)amino)phenoxy)propoxy)phthalonitrile. All compounds were characterized using a combination of analytical and spectroscopic techniques such 1H, [Formula: see text]C NMR, FT-IR, UV-vis and MS spectral data. The molecular geometry and gauge including atomic orbital (GIAO) 1H and [Formula: see text]C chemical shift values of the compounds in the ground state have also been calculated using B3LYP with the 6–31G([Formula: see text] basis set. The chemical shift of the optimized molecular structure is compared with the experimental chemical shift values.

scholarly journals REGRAS: an auxiliary program for pattern recognition and substructure elucidation of monoterpenes

2001 ◽  
Vol 15 (2) ◽  
pp. 65-98 ◽  
Author(s):  
Marcelo J. P. Ferreira ◽  
Gilberto V. Rodrigues ◽  
AntÔnio J. C. Brant ◽  
Vicente P. Emerenciano
Keyword(s):  
Pattern Recognition ◽  
Chemical Shift ◽  
Nmr Data ◽  
Auxiliary Program ◽  
C Nmr

The main purpose of this paper is to present a procedure that utilizes13C NMR for pattern recognition and substructure elucidation of monoterpenes. By this reason, a novel version of the REGRAS program was developed for the specialist SISTEMAT system. This program carries out an analysis of the13C NMR data from a given compound and, from characteristic chemical shift ranges, recognizes the substructures and the skeleton present in a compound. At the end of this procedure, the program displays as analysis results the likely skeletons and substructures of the substance in question. The REGRAS program was tested on skeleton elucidation of 30 monoterpenes from the most varied skeleton types, exhibiting excellent results in skeleton and substructure prediction processes.

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