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.

13C and 119Sn NMR spectra of diphenyl- and dibenzyltin(IV) compounds and their complexes

1990 ◽  
Vol 55 (5) ◽  
pp. 1193-1207 ◽  
Author(s):  
Jaroslav Holeček ◽  
Antonín Lyčka ◽  
Karel Handlíř ◽  
Milan Nádvorník
Keyword(s):  
Internal Structure ◽  
Coordination Sphere ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spectral Parameters ◽  
The Real ◽  
119Sn Nmr ◽  
C Nmr

13C and 119Sn NMR spectra of diphenyl- and dibenzyltin(IV) compounds have been studied in solutions of coordinating and non-coordinating solvents. Regions of values of the δ(119Sn) chemical shifts have been determined which characterize individual types of coordination of the central tin atom. The values of 13C NMR spectral parameters, the δ(13C) chemical shifts and nJ(119Sn, 13C) coupling constants, have been used to describe the real shapes of coordination sphere of the central tin atom and to discuss the internal structure of the organic substituents and of the nature of their bonding linkage to the tin atom.

29Si, 13C and 31P NMR spectra of silicon-substituted ω-diphenylphosphinoalkyl silanes, (CH3)3-n(OC2H5)nSi(CH2)mP(C6H5)2

1982 ◽  
Vol 47 (3) ◽  
pp. 793-801 ◽  
Author(s):  
Jan Schraml ◽  
Martin Čapka ◽  
Harald Jancke
Keyword(s):  
Nmr Spectra ◽  
31P Nmr ◽  
Chemical Shifts ◽  
Additivity Rule ◽  
Ethoxy Group ◽  
Spectral Parameters ◽  
Nmr Spectrum ◽  
Nmr Parameters ◽  
13C And 31P Nmr ◽  
C Nmr

29Si, 13C, and 31P NMR spectra of a series of compounds of the structure (CH3)3-n(C2H5O)n.Si(CH2)mP(C6H5)2 (m = 1-6, n = )-3) are reported and assigned. Using monodeutero derivative of the compound with m = 3 and n = 0 an earlier assignment of 13C NMR spectrum is confirmed, but the assignment in the compounds with m = 4 is reversed. Introduction of ethoxy groups leads to violation of additivity rule for the 13C chemical shifts in the derivatives with m = 1. In all derivatives presence of one ethoxy group in the molecule has a profound effect on 31P chemical shift which is not changed by any further increase in the number of ethoxy groups in the molecule. The changes in 29Si chemical shifts follow the pattern known from other series of compounds. The observed trends in NMR parameters with changing n and m values can be explained by an interaction between phosphorus and oxygen atoms. Possible connections between the spectral parameters and catalysis employing the studied compounds are discussed.

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.

FT-IR and 13C-NMR Correlations for Some N-Substituted Azoles and Benzazoles

1995 ◽  
Vol 49 (8) ◽  
pp. 1111-1119 ◽  
Author(s):  
José Elguero ◽  
Manuel Gil ◽  
Nerea Iza ◽  
Carmen Pardo ◽  
Mar Ramos
Keyword(s):  
Carbon Tetrachloride ◽  
13C Nmr ◽  
Empirical Equation ◽  
Chemical Shifts ◽  
Statistic Analysis ◽  
Spectral Parameters ◽  
Nmr Parameters ◽  
Hammett Constants ◽  
Ft Ir ◽  
C Nmr

The FT-IR (in carbon tetrachloride) and 13C-NMR (in deuterochloroform) spectra of six p-substituted aniline derivatives, as reference compounds, and nine 1- p-aminophenyl-azoles and benzazoles were recorded. The measured spectral parameters from FT-IR were symmetric, vs(NH2), and antisymmetric, vas(NH2), stretching fundamentals and their band intensity ratio, A( vas)/ A( vs), while the corresponding 13C-NMR parameters were C-1 to C-4 chemical shifts of 1- p-aminophenyl carbons. Different IR and 13C-NMR spectral parameters and Hammett constants σp (or σp-) were correlated, and statistic analysis of the results permitted an estimation of σp values of the nine (azol-1-yl) substituents. An empirical equation to calculate the Hammett constants of new azoles and benzazoles is proposed.

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.

NMR study of the protonation of domoic acid

1992 ◽  
Vol 70 (4) ◽  
pp. 1156-1161 ◽  
Author(s):  
John A. Walter ◽  
Donald M. Leek ◽  
Michael Falk
Keyword(s):  
Nmr Spectra ◽  
Domoic Acid ◽  
Spectral Parameters ◽  
Protonation Site ◽  
Nmr Study ◽  
C Nmr

The 1H and 13C NMR spectra of the amnesic shellfish poison, domoic acid, in H2O and D2O solutions have been studied as a function of pH or pD. The results yielded the NMR spectral parameters for each of the five protonation stages of domoic acid, provided accurate pKa values, and enabled each pKa to be associated with a particular protonation site.

Nonbonded and interactions in 2-(4-chlorophenylthio) benzaldehyde in solution. An average skew conformation

1992 ◽  
Vol 70 (9) ◽  
pp. 2375-2380 ◽  
Author(s):  
Ted Schaefer ◽  
Lina B.-L. Lee ◽  
Rudy Sebastian
Keyword(s):  
Title Compound ◽  
Chemical Shifts ◽  
Minimum Energy ◽  
Lone Pair ◽  
Phenyl Group ◽  
Coupling Constants ◽  
Spectral Parameters ◽  
Text Interaction ◽  
The One

The 1H nuclear magnetic resonance spectral parameters are reported for 4.0 mol% solutions of 2-(4-chlorophenylthio) benzaldehyde in CS2/C6D12 and acetone-d6 at 300 K. In CS2 the O-syn conformer is 36% abundant, rising to 50% in acetone-d6. These abundances are compared to those of the O-syn and O-trans conformers of 2-(alkylthio) benzaldehydes in CCl4, solution. On the basis of coupling constants and chemical shifts it is concluded that the skew conformer of the title compound is very likely the one of minimum energy in both solutions. In the skew conformer the plane of the 4-chlorophenyl group lies perpendicular to the CSC plane and also to that of the other aromatic moiety. It is suggested that the [Formula: see text] interaction is rather weak and that the population of the O-syn conformer is controlled by the orientation of the mainly 3p lone-pair orbital on sulfur. At best, the [Formula: see text] interaction is attractive only when the 3p orbital lies perpendicular to the plane of the formyl group. The skew conformation of the title compound is contrasted to the skew conformation of 2-hydroxyphenyl phenyl sulfide in which, however, the role of the two aromatic planes is reversed; the 3p orbital now lies in or near the plane of the phenyl group COH due to an attractive [Formula: see text] interaction.

Conformational consequences of intramolecular hydrogen bonding by OH to the directional lone-pair of sulfur in derivatives of methyl phenyl sulfide, diphenyl sulfide, and diphenyl disulfide

1982 ◽  
Vol 60 (3) ◽  
pp. 342-348 ◽  
Author(s):  
Ted Schaefer ◽  
Salman R. Salman ◽  
Timothy A. Wildman ◽  
Peter D. Clark
Keyword(s):  
Lone Pair ◽  
Phenyl Group ◽  
Intramolecular Hydrogen Bonding ◽  
Spectral Parameters ◽  
Phenyl Sulfide ◽  
Methyl Phenyl Sulfide ◽  
Twist Conformation ◽  
Diphenyl Disulfide ◽  
Conformational Determinant ◽  
Intramolecular Hydrogen

Complete spectral parameters for the 1H nmr spectra of 2-hydroxyphenyl methyl sulfide, 2, 2-hydroxyphenyl phenyl sulfide, 3, bis(2-hydroxy-3-tert-butyl-5-methylphenyl) sulfide, 4, and bis(2-hydroxyphenyl) disulfide, 5, are reported for CCl4 solutions at 305 K. For 2 the parameters are consistent only with a conformation in which the C—S—C plane is roughly perpendicular to the aromatic plane. The conformational determinant is the [Formula: see text] hydrogen bond which forces the mainly 3p orbital on sulfur into the benzene plane. In 3 a similar arrangement is found about the sulfur atom, with the phenyl group lying in the C—S—C plane and therefore perpendicular to the hydroxyphenyl plane (skew conformation). In 4 two [Formula: see text] hydrogen bonds exist, yielding a gable (twist) conformation. Compound 5 exists in the axial conformation with probable C2 symmetry, the CSSC dihedral angle and the CCSS torsion angles all being near 90°. For none of the compounds is there any evidence for [Formula: see text] interactions.

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.

1H nuclear magnetic resonance and molecular orbital studies of the internal rotational potential and electron delocalization in triphenylphosphine

1993 ◽  
Vol 71 (5) ◽  
pp. 639-643 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Frank E. Hruska
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Molecular Orbital ◽  
Lone Pair ◽  
Electron Delocalization ◽  
Spectral Parameters ◽  
Internal Motions ◽  
Diamagnetic Anisotropy ◽  
1H Nuclear Magnetic Resonance ◽  
Nuclear Magnetic

The 1H nuclear magnetic resonance spectral parameters are reported for triphenylphosphine as solutions in CS2/C6D12 and acetone-d6 at 300 K. The internal rotational potential opposing torsion about the P—C bond is computed by AMI and STO-3G MO methods. The computed potentials are used to calculate the average shielding of the para protons caused by the diamagnetic anisotropies of the neighbouring phenyl groups. The results are used to estimate the degree of electron delocalization from the lone pair on phosphorus. The extent of delocalization depends on the internal motions and comparisons are made with phenylphosphine. The maximum possible screening of the para protons in phenylphosphine is calculated as 0.19 ppm for a conformation in which the lone pair on phosphorus is oriented perpendicular to the aromatic plane. The intramolecular rotational potentials then yield 0.029 ppm as the shielding of the para protons in triphenylphosphine due to electron delocalization, just as found for the CS2/C6D12 solution after correction for diamagnetic anisotropy fields.

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