Photochromic systems. Part 1. Structural and spectroscopic study of photochromically active products of Stobbe condensation. 2,3-Dibenzylidenesuccinic acid and its anhydride

1990 ◽  
Vol 68 (5) ◽  
pp. 741-746 ◽  
Author(s):  
P. Adriaan Davidse ◽  
Jan L. M. Dillen ◽  
Anton M. Heyns ◽  
Tomasz A. Modro ◽  
Petrus H. van Rooyen
Keyword(s):  
Cinnamic Acid ◽  
Structural Changes ◽  
Chemical Shifts ◽  
Spectroscopic Properties ◽  
Shielding Effect ◽  
Electron Charge ◽  
Hydrogen Atoms ◽  
Steric Strain ◽  
Space Group ◽  
Charge Densities

E,E-2,3-Dibenzylidenesuccinic acid (2) and its anhydride (1) were synthesized, their crystal structures and 1H and 13C nuclear magnetic resonance spectra were determined, and electron charge densities of carbon atoms were calculated. These results were related to the corresponding data available for E-cinnamic acid (3) in order to evaluate the effect of structural changes in a series 3 → 2 → 1 on the molecular parameters and spectroscopic properties of the cinnamic system. In the molecule of 2 most of the steric strain is released by the rotation about the C(α)—C(α′) bond giving rise to a structure consisting of two, approximately independent, cinnamic acid moieties. In 1, severe steric strain is introduced, as demonstrated by the unusually large values of the CCC bond angles exocyclic with respect to the anhydride ring, as well as by significant deviations from the plane of the cinnamic skeleton. The geometry of 1 results in an intramolecular shielding of the aromatic hydrogen atoms due to the proximity of the two benzene rings; this shielding effect for the ortho, meta, and para hydrogen atoms correlates well with the intramolecular distances between the corresponding positions of both rings. The common linear relationship between 13C chemical shifts and the electron charge densities on the given carbon atom has been obtained for compounds 1, 2, and 3.Crystal data. Anhydride (1): space group P21/c with a = 13.536(3), b = 14.391(3), c = 7.159(1) Å; β = 98.69(1)°; Rw = 0.029 and R = 0.055. Succinic acid (2): space group [Formula: see text] with a = 8.881(3), b = 9.786(1), c = 11.355(3) Å; α = 85.56(1), β = 88.76(2), γ = 69.46(2)°; Rw = 0.048 and R = 0.081. This compound cocrystallizes with one molecule of the solvent (acetic acid). Keywords: photochromic, cinnamic, succinic.

Synthesis, Structures and Spectroscopic Properties of 1 : 1 Complexes of Gold(I) Halides with Tricyclohexylphosphine, [Au(PCy3)X], X = Cl, Br and I

1999 ◽  
Vol 52 (4) ◽  
pp. 271 ◽  
Author(s):  
Raymond C. Bott ◽  
Graham A. Bowmaker ◽  
Robbie W. Buckley ◽  
Peter C. Healy ◽  
M. C. Senake Perera
Keyword(s):  
Solid State ◽  
Chemical Shifts ◽  
Far Infrared ◽  
Spectroscopic Properties ◽  
Chain Structure ◽  
Phosphine Ligands ◽  
Zigzag Chain ◽  
Conformational Structure ◽  
Space Group ◽  
Structure Determinations

Two-coordinate gold(I) complexes, [Au(PCy3)X] (PCy3 = tricyclohexylphosphine, X = Cl, Br and I), have been prepared by reaction of stoichiometric quantities of [NBu4] [AuX2] and PCy3 in dimethylformamide and, for X = Cl and Br, by anodic dissolution of metallic gold in a solution of aqueous HX and PCy3 in acetonitrile. The complexes were characterized by solution and solid-state 31 P n.m.r. spectroscopy, far-infrared spectroscopy and single-crystal X-ray structure determinations. The chloride, bromide and iodide complexes form an isomorphous series, crystallizing in the triclinic space group P 1- (a ≈ 9·3, b ≈ 10·3, c ≈ 10·9 Å, α ≈ 88, β ≈ 80, γ ≈ 77°) as discrete molecules which stack in parallel head-to-tail mode to form a zigzag chain of gold atoms along the crystallographic c axis. Au ··· Au separations are 5·71, 6·20 Å for X = Cl, 5·72, 6·17 Å for X = Br and 5·74, 6·20 Å for X = I. The iodide also crystallizes as an orthorhombic form in space group Pnma (a 16·809(4), b 14·373(5), c 8·623(3) Å) with a different conformational structure for the PCy3 ligand and loss of the zigzag chain structure. Far-infrared spectra of the complexes show ν(AuX) at 332, 324 cm-1 for X = Cl and 232 cm-1 for X = Br with multiple bands in the region 150−200 cm-1 for both iodide complexes, precluding definitive assignment of ν(AuI). Solution 31 P n.m.r. spectra in chloroform give sharp single peaks with chemical shifts of 54·5, 56·6 and 59·9 ppm for X = Cl, Br and I respectively. The solid-state CPMAS 31 P n.m.r. spectra also yield single peaks with chemical shifts of 55 (Cl), 58 (Br) and 63 ppm (I) for the triclinic complexes and 57 ppm for the orthorhombic iodide. The chemical shift differences between the two forms of the iodide and between the complexes in the solution and solid states are ascribed to variations in the conformational structure of the phosphine ligands.

CNDO/2-Elektronenladungsdichten und 13C-chemische Verschiebungen von Phenylacetylenen / CNDO/2-Electron Charge Densities and 13C-Chemical Shifts of Phenylacetylenes

1972 ◽  
Vol 27 (12) ◽  
pp. 1772-1776 ◽  
Author(s):  
L Klasinc ◽  
J.V. Knop ◽  
H.-J Meiners ◽  
W Zeil
Keyword(s):  
Charge Transfer ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Electron System ◽  
Total Charge ◽  
Electron Charge ◽  
Substituted Benzenes ◽  
Charge Densities ◽  
Inductive Effects ◽  
Monosubstituted Benzenes

AbstractThe 13C FT NMR spectra of phenylacetylene (1), p-methoxyphenylacetylene (2), p-fluorophenyl-acetylene (3), p-chlorophenylacetylene (4), p-bromophenylacetylene (5), p-ethylphenylacetylene (6) and p-isopropylphenylacetylene (7) as well as of a number of monosubstituted benzenes have been measured. The 13 C-chemical shifts in these compounds are correlated with the total charge densities at the corresponding carbon atoms, calculated by the CNDO/2 method. The present results show that a simple additivity exists between 13C-chemical shifts in substituted benzenes, phenylacetylene and substituted phenylacetylenes and that practically no charge transfer between the linked sub-stituted phenyl and the ethinyl groups takes place. The interaction of the ethinyl substituent and the π-electron system can mainly be attributed to inductive effects.

scholarly journals Thermochemical and Structural Analysis of Tautomers of Sulfur and Selenium Modified RNA Nucleobases

2019 ◽  
Vol 2 (2) ◽  
pp. 47-48
Author(s):  
Megan Joy ◽  
Alex Brown ◽  
Arturo Mora Gomez ◽  
Maria Rossano-Tapia ◽  
Shyam Parshotam
Keyword(s):  
Ir Spectra ◽  
Structural Changes ◽  
Chemical Properties ◽  
Hydrogen Atoms ◽  
Relative Population ◽  
Geometry Analysis ◽  
Physical And Chemical ◽  
Modified Nucleobases ◽  
Relative Gibbs Free Energy ◽  
And Chemical Properties

Nucleobases (adenine, cytosine, guanine, and uracil), the four molecules that forms RNA, have been found to be useful in probing in the human body when modified because they can emit light. Non-modified nucleobases do not exhibit emissive properties and cannot be used as probes. Some of the modifications include the substitution of nitrogen atoms with sulfur and selenium, and the resulting modified nucleobases give place to the so-called tz- and ts- RNA alphabets, respectively. Therefore, the aim of this project was to provide insights about the viability, from a computational perspective, of using the modified nucleobases as probes, evaluating the differences in thermochemical, structural and emissive properties of the modified nucleobases with respect to the non-modified ones. Nucleobases can coexist with other modified nucleobases or tautomers, molecules that differ due to the change in position of hydrogen atoms in a molecule’s structure and as a result have different physical and chemical properties. The thermochemical properties evaluation mainly consisted in the computation of the relative Gibbs Free Energy (G), which is related to the fraction F, an index of the relative population among tautomers. This was done using Gaussian 09 software by performing geometry analysis and frequency computations on each one of the tautomers. By comparing the equilibrium fractions, it was determined that in both cases, tz- and ts- guanine and cytosine exist principally in the form of one of their tautomers (Cytosine 2 and Guanine 2) as in the case of the non-modified cases. After confirming which tz- and ts- tautomers were the ones with the largest probable population, infrared (IR) and ultraviolet-visible (UV-vis) spectra were obtained. The IR spectra of selenium and sulfur tautomers of guanine and cytosine indicated that the tautomers had peaks at similar frequencies with respect to each other, however, the intensities varied, implying slight structural changes between the tautomers. On the other hand, the UV-vis spectra showed a change in peak positions between the tautomers with sulfur and selenium, suggesting that the change between sulfur and selenium has an effect on the spectra by shifting the peaks from the original molecules’ λmax values. Their relative population fractions show that only the canonical forms of the modified nucleobases exist in a larger extent than the rest of their tautomer forms. In addition, the features in their UV-vis and IR spectra allow these tautomers to be differentiated from each other.

Nuclear Magnetic Resonance Chemical Shifts of some Monosubstituted Isothiazoles

1975 ◽  
Vol 53 (4) ◽  
pp. 596-603 ◽  
Author(s):  
Roderick E. Wasylishen ◽  
Thomas R. Clem ◽  
Edwin D. Becker
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Charge Densities ◽  
Monosubstituted Benzenes ◽  
Proton Chemical Shifts ◽  
Nuclear Magnetic

Carbon-13 and proton chemical shifts have been measured for several monosubstituted isothiazoles. Substituent effects upon these chemical shifts are compared with those observed for monosubstituted benzenes, pyridines, and thiophenes. In general the observed substituent effects in the isothiazoles and thiophenes closely parallel one another. Correlations between the observed carbon-13 Chemical shifts and CNDO/2 calculated charge densities are examined.

Erratum: Electron charge densities at conduction-band edges of semiconductors

1987 ◽  
Vol 35 (17) ◽  
pp. 9308-9309
Author(s):  
Steven L. Richardson ◽  
Marvin L. Cohen ◽  
Steven G. Louie ◽  
James R. Chelikowsky
Keyword(s):  
Conduction Band ◽  
Electron Charge ◽  
Charge Densities

CMR CHEMICAL SHIFTS AND TOTAL CHARGE DENSITIES OF [2.2]CYCLOPHANES. THE EFFECT OF TRANSANNULAR Π- Π INTERACTION

1977 ◽  
Vol 6 (8) ◽  
pp. 865-868 ◽  
Author(s):  
Tetsuo Takemura ◽  
Kazushi Tokita ◽  
Shoichi Kondo ◽  
Nobuo Mori
Keyword(s):  
Chemical Shifts ◽  
Total Charge ◽  
Charge Densities

scholarly journals Исследование строения, ионной, молекулярной подвижности и термических свойств гидратов пентафторидоцирконата аммония

2019 ◽  
Vol 126 (2) ◽  
pp. 147
Author(s):  
Е.И. Войт ◽  
А.Б. Слободюк ◽  
Н.А. Диденко
Keyword(s):  
Structural Changes ◽  
Chemical Shifts ◽  
Molecular State ◽  
Structural Motif ◽  
Nmr Data ◽  
State Of Water ◽  
Hydrate Number ◽  
Bond Strengths ◽  
Isotropic Chemical Shifts ◽  
Ir And Raman

AbstractThe effect of hydrate number on the structural changes, thermal properties, and ionic (molecular) mobility character in NH_4ZrF_5 ⋅ H_2O, NH_4ZrF_5 ⋅ 0.75H_2O crystal hydrates have been investigated by the methods of IR, Raman, nuclear magnetic resonance (NMR) (^1H, ^19F, including ^19F MAS), and TG-DTA spectroscopy. Differences in crystal hydrate structures—anion structure, molecular state of water, and O–H⋅⋅⋅F, N–H⋅⋅⋅F hydrogen bond strengths—have been corroborated by IR and Raman spectroscopy data. Isotropic chemical shifts of magnetic inequivalent positions have been determined and attributed to crystal structures of the studied compounds by the method of ^19F MAS NMR. It has been established that the removal of water molecules from NH_4ZrF_5 ⋅ H_2O and NH_4ZrF_5 ⋅ 0.75H_2O results in the transformation of chain or layered structures accompanied by the increase of the number of bridge bonds while retaining or increasing the dimensionality of the anion structural motif. According to the ^1H NMR data, the NH $$_{4}^{ + }$$ cation diffusion in NH_4ZrF_5 occurs only in the temperature range of 370–520 K.

scholarly journals Studying the structural and electronic effects of substituted (Bi0.5Na0.5)TiO3

2014 ◽  
Vol 70 (a1) ◽  
pp. C1522-C1522
Author(s):  
Peter Blanchard ◽  
Brendan Kennedy ◽  
Chris Ling
Keyword(s):  
Solid Solutions ◽  
Structural Changes ◽  
Structural Evolution ◽  
Rhombohedral Phase ◽  
Rhombohedral Structure ◽  
Electronic Effects ◽  
Spectra Analysis ◽  
Space Group ◽  
Industry Standard ◽  
Made In

Significant efforts have been made in the development of (Bi0.5Na0.5)TiO3 ferroelectrics as an alternative to the lead-based industry standard PbTi1-xZrxO3.[1] It has also been shown that doping the A- and B-site of (Bi0.5Na0.5)TiO3 can greatly improve the ferroelectric behavior of these materials,[2] possibly due to the formation of two or more ferroelectric phases at a morphotropic phase boundary (MPB). As such, there is a significant interest in understanding the structural changes in (Bi0.5Na0.5)TiO3-based solid solutions. (Bi0.5Na0.5)TiO3 was originally described as adopting a rhombohedral structure in space group R3c, However, the accuracy of this description has been greatly debated. It was recently suggested that (Bi0.5Na0.5)TiO3 actually adopts a monoclinic structure in space group Cc.[3] Given this recent controversy, we investigated the structural evolution of (Bi0.5Na0.5)TiO3-based solid solutions, particularly the (Bi0.5Na0.5)Ti1-xZrxO3 and (1-x)(Bi0.5Na0.5)TiO3–xBiFeO3 solid solutions., using both diffraction and spectroscopy techniques. Diffraction measurements on (Bi0.5Na0.5)TiO3 confirm that both monoclinic Cc and rhombohedral R3c phases are present at room temperature. Diffraction analysis showed that doping (Bi0.5Na0.5)TiO3 with a small amount of (Bi0.5Na0.5)ZrO3 and BiFeO3 can stabilizes the rhombohedral phase. The Ti/Fe K-edge and Zr L3-edge XANES spectra analysis was performed to determine the effects doping has on the local displacement of the B-site cations.

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