Electronic Nature of α-Methoxy, Amino, Cyano, and Mercapto Nitrones

1993 ◽  
Vol 58 (1) ◽  
pp. 125-141 ◽  
Author(s):  
David E. Gallis ◽  
James A. Warshaw ◽  
Bruce J. Acken ◽  
DeLanson R. Crist
Keyword(s):  
Bond Order ◽  
Cyano Group ◽  
Energy Levels ◽  
Lone Pair ◽  
Model Systems ◽  
Electronic Nature ◽  
Versus Model ◽  
Mndo Calculations ◽  
Reverse Substituent Effect ◽  
C Nmr

The electronic nature of various C-substituted nitrones was investigated by IR spectroscopy and 13C NMR as well as MNDO calculations. These include α-methoxy nitrones (imidate N-oxides) RC(OMe)=N(O)t-Bu with R = p-MeOC6H4 (Ia), C6H5 (Ib), p-NO2C6H4 (Ic), and H (Id) and nitrones YCH=N(O)t-Bu with Y = CN (IIIa), n-BuS (IIIb), C6H5CH2NH (IIIc). Upfield 13C shifts of C(α), the iminyl (C=N) carbon, of imidate N-oxides I versus the corresponding imidates are less than the usual upfield shifts of imine N-oxides versus imines, suggesting less buildup of electron density on C(α) in the case of alcoxy nitrones. Charge density and π bond order values from MNDO calculations for C-methoxy-C-phenyl nitrones versus model systems confirm this result and indicate a more localized C=N π bond in nitrones bearing an α-methoxy group. For N-tert-butyl nitrones with an α heteroatom (nitrogen or sulfur), phenyl, or cyano group, C(α) shifts move downfield for π-donating groups and upfield for π-accepting groups. This "reverse substituent effect" as well as C=N stretching frequencies can also be readily explained by C=N π bond containment by lone pair groups. The reported enhanced cycloaddition reactivity of α-alkoxy nitrones and their electrochemical behavior are discussed in terms of HOMO energy levels.

The basicity of phosphines

1982 ◽  
Vol 60 (6) ◽  
pp. 716-722 ◽  
Author(s):  
Tim Allman ◽  
Ram G. Goel
Keyword(s):  
Lone Pair ◽  
Titration Method ◽  
Spectral Parameters ◽  
C Nmr

The basicities of the triarylphosphines P(4-XC6H4)3 (X = Cl, F, H, CH3, CH3O, (CH3)2N), P(3-CH3C6H4)3, and P(2-CH3C6H7)3 as well as the trialkylphosphines P(t-Bu)3 and PCy3 have been measured by the nitromethane titration method. The range of basicity available by aryl substitution is very large, being pKa = 8.65 for X = (CH3)2N to 1.03 for X = Cl. The most basic phosphine is P(t-Bu)3 whose pKa = 11.40. The measured basicities correlate well with σp, [Formula: see text], and ν as well as with the lone pair ionisation potentials of the triarylphosphines. Generally the 1H, 31P, and 13C nmr spectral parameters of the free and protonated phosphines do not correlate well with pKa.

NMR Spectroscopic Studies of Thialene (Cyclopenta[b]thiapyran) and Isothialene (Cyclopenta[c]thiapyran)

1993 ◽  
Vol 58 (1) ◽  
pp. 113-120 ◽  
Author(s):  
Robert F. X. Klein ◽  
Václav Horák ◽  
Arthur G. Anderson
Keyword(s):  
Chemical Shift ◽  
Bond Order ◽  
Spectroscopic Studies ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Vicinal Coupling Constant ◽  
Spectral Parameters ◽  
First Order ◽  
Nmr Techniques ◽  
C Nmr

1H and 13C NMR spectral parameters are reported for the S-pseudoazulenes thialene (cyclopenta[b]thiapyran) (I) and isothialene (cyclopenta[c]thiapyran) (II). Both compounds display complex first order spectra, with thialene having 10 and isothialene 14 of 15 possible coupling constants. Complete unambiguous assignments of all protons and non-quaternary carbons were made via 2-dimensional NMR techniques and PPP-SCF π-electron density/chemical shift and π-bond order/vicinal coupling constant correlations.

Polar effects on 13C NMR chemical shifts and rotational barriers of amides. A dual substituent parameters analysis of N,N-dimethyl-3-(5-substituted-2-furyl)-acrylamides

1987 ◽  
Vol 52 (2) ◽  
pp. 409-424 ◽  
Author(s):  
Zdeněk Friedl ◽  
Stanislav Böhm ◽  
Igor Goljer ◽  
Anna Piklerová ◽  
Daniela Poórová ◽  
...  
Keyword(s):  
Substituent Effect ◽  
Chemical Shifts ◽  
Polar Effect ◽  
Dominant Factor ◽  
Side Chain ◽  
Nmr Chemical Shifts ◽  
Resonance Effects ◽  
H Nmr ◽  
Reverse Substituent Effect ◽  
C Nmr

13C NMR chemical shifts were measured for sixteen N,N-dimethyl-3-(5-substituted-2-furyl)-acrylamides in CDCl3 at 21 °C; the barriers of rotation about the C-N bond ΔGc° were determined by using the 1H NMR coalescence method, and the positions of the IR bands of the ν(C=O) stretching vibrations were measured. The dual substituent parameters (DSP) analysis of the 13C NMR chemical shifts for atoms of the vinylcarboxamide side chain -C(3)H=C(2)H-C(1)=O(-N) gives evidence that the chemical shifts for the C-1 and C-3 atoms are controlled primarily by polar effects (δ(C-3) = -3.12σI - 1.03σR0; λ = ρI/ρR = 3.0), which exert a reverse substituent effect on these atoms. Similarly, the DSP analysis of the ΔGc° and ν(C=O) data shows that the dominant factor of the total substituent effect is the polar effect (λ = 1.95 and 1.70, respectively). A confrontation of the results of the DSP analysis with the CNDO/2 calculated electron densities at the corresponding atoms demonstrates that the reactivity of the entire vinylcarboxamide side chain can be well explained in terms of a combination of the polar effect (π-electron polarization) with resonance effects.

Hypercoordinate β-carbon in Grubbs and Schrock olefin metathesis metallacycles

2015 ◽  
Vol 44 (40) ◽  
pp. 17660-17672 ◽  
Author(s):  
Premaja R. Remya ◽  
Cherumuttathu H. Suresh
Keyword(s):  
Electron Density ◽  
Olefin Metathesis ◽  
Bond Order ◽  
Structural Bond ◽  
Nmr Data ◽  
C Nmr

From the analysis of structural, bond order, electron density and 13C NMR data of a large variety of ruthenacyclobutanes and tungstenacyclobutanes, we show that the Cβ of the metallacycle is pentacoordinate.

Multivariate Regression with Substituent Shift Increments. III. 2,5-Disubstituted Furans

1999 ◽  
Vol 64 (10) ◽  
pp. 1696-1708
Author(s):  
Miroslav Holík ◽  
Zdeněk Friedl ◽  
Štefan Marchalín
Keyword(s):  
Chemical Shift ◽  
Multivariate Regression ◽  
Bond Order ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Numerical Estimation ◽  
Correct Assignment ◽  
Diamagnetic Contribution ◽  
Substituted Furans ◽  
C Nmr

Six series of 2-X-5-Y-substituted furans were used for multivariate regression of 13C NMR chemical shifts with four substituent shift increments (SSI). Some of these series were measured in CDCl3 and DMSO-d6 on different spectrometers to exclude possible sources of deviation from the general trends. Program ASSIGN was written for visual and numerical estimation of correct assignment of 13C NMR spectra in the series of derivatives. Multivariate regression proved that the corresponding position in benzenes and furans are not affected by the substituents in the same way: in 2-X-5-Y-substituted furans, the "ortho" position requires correction for the different bond order, the "meta" 13C chemical shift is probably affected by change in diamagnetic contribution of the Y group, and "para" position behaves like another "ortho" position in the molecule.

scholarly journals Words for maximal Subgroups of Fi24‘

2019 ◽  
Vol 17 (1) ◽  
pp. 1491-1500
Author(s):  
Faisal Yasin ◽  
Adeel Farooq ◽  
Chahn Yong Jung
Keyword(s):  
Finite Group ◽  
Group Theory ◽  
Finite Number ◽  
Physical Properties ◽  
Open Problem ◽  
Bond Order ◽  
Energy Levels ◽  
Maximal Subgroups ◽  
Mathematical Application ◽  
A Finite Group

AbstractGroup Theory is the mathematical application of symmetry to an object to obtain knowledge of its physical properties. The symmetry of a molecule provides us with the various information, such as - orbitals energy levels, orbitals symmetries, type of transitions than can occur between energy levels, even bond order, all that without rigorous calculations. The fact that so many important physical aspects can be derived from symmetry is a very profound statement and this is what makes group theory so powerful. In group theory, a finite group is a mathematical group with a finite number of elements. A group is a set of elements together with an operation which associates, to each ordered pair of elements, an element of the set. In the case of a finite group, the set is finite. The Fischer groups Fi22, Fi23 and Fi24‘ are introduced by Bernd Fischer and there are 25 maximal subgroups of Fi24‘. It is an open problem to find the generators of maximal subgroups of Fi24‘. In this paper we provide the generators of 10 maximal subgroups of Fi24‘.

scholarly journals A study of 13C–15N couplings and revised 13C shieldings in 15N-enriched E-acetophenone oximes

1976 ◽  
Vol 54 (5) ◽  
pp. 790-794 ◽  
Author(s):  
Gerald W. Buchanan ◽  
Brian A. Dawson
Keyword(s):  
Chemical Shifts ◽  
Lone Pair ◽  
Methoxyl Group ◽  
Coupling Constant ◽  
Absolute Value ◽  
Lanthanide Induced Shifts ◽  
Nitrogen Lone Pair ◽  
Acetophenone Oxime ◽  
Cndo Calculations ◽  
C Nmr

13C nmr chemical shifts and 13C–15N couplings through one, two, and three bonds are reported for E-acetophenone oxime and five para-substituted derivatives. It is shown that earlier assignments for three of these compounds, based on lanthanide induced shifts and CNDO calculations, are erroneous. With the exception of the methoxyl group, couplings are relatively insensitive to the nature of the para-function. For geminal 13C–15N interactions, the proximity of the nitrogen lone pair to the carbon terminus greatly enhances the absolute value of the coupling constant.

DFT investigation on organic dyes with cross-conjugated cyano groups

2014 ◽  
Vol 13 (01) ◽  
pp. 1450008
Author(s):  
Chunhe Yang ◽  
Aiwei Tang ◽  
Fujun Zhang ◽  
Feng Teng
Keyword(s):  
Density Functional ◽  
Molecular Conformation ◽  
Organic Dyes ◽  
Cyano Group ◽  
Energy Levels ◽  
Orbital Energy ◽  
Dye Molecules ◽  
Conjugated Molecules ◽  
Functional Theory ◽  
Cyano Groups

Organic dye molecules with the acceptor moieties, cyano groups, cross-conjugated to the donor moieties, have been investigated theoretically. Density functional theory (DFT) calculations on such cross-conjugated molecules reveal the effects of cross-conjugation on the geometric and electronic structures of the molecules. The cross-conjugated cyano groups in the dye molecules are found effective to alter the charge population and the frontier orbital energy levels of the dyes. The effects of cross-conjugation of cyano group on the molecular conformation, the charge transfer, and polarity of the dyes are discussed.

Concerning the conformational preferences of the 2-cyano derivatives of oxane, thiane, and selenane

2010 ◽  
Vol 88 (8) ◽  
pp. 831-838 ◽  
Author(s):  
Michael H. Benn ◽  
Yan Yan Huang ◽  
Frank Johannsen ◽  
Michael O’Reilly ◽  
Masood Parvez ◽  
...  
Keyword(s):  
Bond Length ◽  
Cyano Group ◽  
Lone Pair ◽  
Nbo Analysis ◽  
Orbital Interaction ◽  
Anomeric Effect ◽  
Model Compounds ◽  
Conformational Preferences ◽  
Lone Pair Electrons ◽  
Derivatives Of

This paper investigates the origin of the anomalous anomeric effect in merosinigrin, a 2-cyanothiane in which the cyano group is axial as expected for the anomeric effect, but in which bond distances are opposite to that expected from the nS→[Formula: see text] orbital interaction, which underlies the classical anomeric effect. The model compounds, 2-cyanooxane, 2-cyanothiane, and 2-cyanoselenane, were synthesized and studied both experimentally and computationally. Both the thia and selena systems displayed an even higher preference for the axial conformation than the oxa system but also exhibited the bond length anomalies found previously in merosinigren. Natural bond order (NBO) analysis of the B3LYP/6–311+G(3df,2p) wave functions of the axial and equatorial forms of the three systems confirmed a weakening of the n→σ* orbital interaction in the O, S, and Se series, and a strengthening of a σ–π*(CN) interaction that explains the bond length reversals observed in the S and Se systems. It also revealed a new mechanism, n→π*, namely, a through-space interaction between the nonbonded lone pair electrons of the heteroatom and the π* orbital of the cyano group, which selects for the axial conformation.

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