Merostabilization in radical ions, triplets, and biradicals. 5. The thermal cis–trans isomerization of para-substituted tetraphenylethylenes

1981 ◽  
Vol 59 (3) ◽  
pp. 609-620 ◽  
Author(s):  
William J. Leigh ◽  
Donald R. Arnold
Keyword(s):  
Transition State ◽  
Benzene Solution ◽  
Substituent Effects ◽  
Thermal Isomerization ◽  
Radical Ions ◽  
Trans Isomers ◽  
X Ray ◽  
System A ◽  
Cis And Trans Isomers ◽  
Cis And Trans

The cis- and trans-isomers of four para-substituted (three disubstituted and one tetrasubstituted) tetraphenylethylenes have been synthesized, separated, and characterized by either dipole moment or X-ray analysis. The rates of thermal isomerization of the disubstituted derivatives in benzene solution correlate with a substituent parameter reflecting substituent effects on benzylic radical stabilities (σ•), which reflects the biradical nature of the transition state for thermal isomerization in this system. A significant rate enhancement is observed for the tetrasubstituted derivative, in which merostabilization of the transition state is possible.The Arrhenius parameters for thermal isomerization in benzene were determined. From the variation observed for the disubstituted derivatives, an estimate of 35.5 kcal mol−1 for the rotational barrier in tetraphenylethylene is obtained. The activation energy for thermal isomerization of the tetrasubstituted derivative is 2 kcal mol−1 lower than those of the other three; this provides an assessment of the importance of merostabilization in this system.The thermal isomerization of some related olefins (e.g. bianthrylidenes and indigo derivatives) is discussed in light of these results.

Gold complexes of ditelluridoimidodiphosphinate ligands — Reversible oxidation of Au(I) to Au(III) via insertion of gold into a phosphorus–tellurium bond

2009 ◽  
Vol 87 (1) ◽  
pp. 39-46 ◽  
Author(s):  
Dana J Eisler ◽  
Stuart D Robertson ◽  
Tristram Chivers
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Trans Isomers ◽  
Nmr Studies ◽  
Gold Complexes ◽  
X Ray ◽  
Cis And Trans Isomers ◽  
Cis And Trans ◽  
Insertion Process

The reaction of (THT)AuCl with (TMEDA)Na[N(TePR2)2] (R = Ph, i-Pr, t-Bu) produces a series of gold (III) complexes of the type [{R2PNP(Te)R2}Au(µ-Te)]2 (4a, R = i-Pr; 4b, R = Ph; 4c, R = t-Bu) rather than the expected homoleptic Au(I) complexes of the ditelluridoimidodiphosphinate ligands. A combination of solution- and solid-state NMR studies shows that both cis and trans isomers of 4a–4c are formed in these reactions. X-ray structural determinations of the trans isomers of 4a–4c reveal a centrosymmetric arrangement with a central four-membered Au2Te2 ring formed by the formal insertion of gold into a P–Te bond; this insertion process was shown to be reversible upon addition of PPh3 to 4a to give the monomeric gold(I) complex Ph3PAu[N{TeP(i-Pr)2}2]. The X-ray structure of cis-4b is also described.Key words: gold, tellurium, redox, X-ray structures, imidodiphosphinate.

Synthesis and characterization of cis and trans isomers of [NiL2(NCS)2] [L=1-(2-aminoethyl)pyrrolidine]: X-ray single-crystal structures

Polyhedron ◽  
2000 ◽  
Vol 19 (15) ◽  
pp. 1803-1807 ◽  
Author(s):  
Inamur Rahaman Laskar ◽  
Tapas Kumar Maji ◽  
Siddhartha Chaudhuri ◽  
Ashutosh Ghosh ◽  
Nirmalendu Ray Chaudhuri
Keyword(s):  
Single Crystal ◽  
Crystal Structures ◽  
Synthesis And Characterization ◽  
Trans Isomers ◽  
X Ray ◽  
Single Crystal Structures ◽  
Cis And Trans Isomers ◽  
Cis And Trans

Syntheses, electrochemistry and photophysical properties of a series ofmeso-pyridylpentafluorophenylporphyrins

2010 ◽  
Vol 14 (11) ◽  
pp. 975-984 ◽  
Author(s):  
Emmanuel Z. Moreira ◽  
Alba D.Q. Ferreira ◽  
Cláudio Roberto Neri ◽  
Sumitra Mukhopadhyay ◽  
Sérgio Dovidauskas ◽  
...  
Keyword(s):  
Electrochemical Properties ◽  
Photophysical Properties ◽  
Synthesis And Characterization ◽  
Redox Potentials ◽  
Trans Isomers ◽  
X Ray ◽  
X Ray Crystallography ◽  
Cis And Trans Isomers ◽  
Cis And Trans

This work presents the synthesis and characterization of a series of substituted pyridylpentafluroporphyrins, including the separation of the cis- and trans-isomers, the latter being characterized by X-ray crystallography. The spectroscopic and electrochemical properties of the series are dependent on the number of electron withdrawing pentafluorophenyl substituent, but they do not depend on the symmetry of the molecule. Ongoing from the monosubstituted to the more substituted pentafluorophenyl porphyrin H2(MPyTFPP) derivative, the Soret bands are slightly red-shifted and their quantum fluorescence yields range from 0.035 to 0.046, consistent with the value of 0.045 for the fully substituted 5,10,15,20-tetrapentafluorophenylporphyrin (dichloromethane solutions). The redox potentials of the reductive processes of monoanion and dianion formation are also sensitive to the number of pentafluoro substituents, shifting 180 mV to more positive values for the P0/P-1process ongoing from the monopentafluoro to the tris-pentafluorophenyl substituted derivative.

Substituted homoallenyl aldehydes and their derivatives. Part 1: Homoallenyl aldehydes and protected hydrazones

2013 ◽  
Vol 67 (1) ◽  
Author(s):  
Juraj Galeta ◽  
Stanislav Man ◽  
Milan Potáček
Keyword(s):  
Triple Bond ◽  
Claisen Rearrangement ◽  
Initial Step ◽  
Sonogashira Coupling ◽  
Trans Isomers ◽  
Vinyl Ethers ◽  
X Ray ◽  
Cis And Trans Isomers ◽  
Cis And Trans ◽  
Sodium Amide

AbstractThe paper presents a simple synthesis of substituted propargyl vinyl ethers and their subsequent thermally-initiated Claisen rearrangement leading to various 3-substituted homoallenyl aldehydes. Several methods, including Sonogashira coupling, base-promoted substitution on the triple bond by sodium amide or butyllithium, and the preparation of substituted propargyl alcohols, were used in the initial step. Phosphate-protected homoallenyl aldehyde hydrazone derivatives were synthesised and fully characterised. The stereochemistry of 9-anthracene carbaldehyde hydrazone, which, surprisingly, afforded both cis and trans isomers, was established using X-ray analysis.

Preparation of cis- and trans-[OsCl2(Me2SO)4], and X-Ray Crystal Structures of the All-S-Bound Isomers

1998 ◽  
Vol 51 (9) ◽  
pp. 807 ◽  
Author(s):  
Andrew M. McDonagh ◽  
Mark G. Humphrey ◽  
David C. R. Hockless
Keyword(s):  
Structural Study ◽  
Trans Isomers ◽  
Triclinic Space Group ◽  
Space Group ◽  
X Ray ◽  
Group I ◽  
Cis And Trans Isomers ◽  
Cis And Trans ◽  
Cis Isomer

Efficient syntheses of the cis and trans isomers of [OsCl2(Me2SO)4] are reported. While a structural study of thetrans isomer confirms the spectroscopically assigned all-S-bound Me2SO configuration, a crystallographic determination of the cis isomer reveals a previously unheralded all-S-bound Me2SO geometry, in contrast to the spectroscopically inferred configuration predominant in solution which has one O-bound ligand. Fortrans-[OsCl2(Me2SO)4], crystals are tetragonal, space group I 4/m, with a 9·092(2), c 11·212(3) Å, Z 2, 566 unique reflections (34 parameters), converging at R 0·026 and Rw 0·032. For cis-[OsCl2(Me2SO)4], crystals are triclinic, space group P-1, with a 8·193(2), b 8·941(3), c 13·837(3) Å, α 79·77(2), β 79·91(2), γ 65·03(2)°, Z 2, 4152 unique reflections (173 parameters), converging at R 0·021 and Rw 0·018.

Synthesis and NMR characterization of the cis and trans isomers of [Ptii(N9-adeH)2(pz)2] and X-ray crystallography of the trans isomer

2007 ◽  
pp. 3966 ◽  
Author(s):  
Karel D. Klika ◽  
Henri Kivelä ◽  
Vladimir V. Ovcharenko ◽  
Ville Nieminen ◽  
Reijo Sillanpää ◽  
...  
Keyword(s):  
Trans Isomer ◽  
Trans Isomers ◽  
X Ray ◽  
X Ray Crystallography ◽  
Cis And Trans Isomers ◽  
Nmr Characterization ◽  
Cis And Trans

Concerning stereochemical assignments from 13C spectra of systems experiencing γ substituent effects. Deshielding antiperiplanar interactions can mislead the unwary

1976 ◽  
Vol 54 (20) ◽  
pp. 3272-3275 ◽  
Author(s):  
W. A. Ayer ◽  
L. M. Browne ◽  
S. Fung ◽  
J. B. Stothers
Keyword(s):  
Substituent Effects ◽  
Methyl Groups ◽  
Hydroxyl Groups ◽  
Trans Isomers ◽  
Cis And Trans Isomers ◽  
Cis And Trans ◽  
Quaternary Carbons

A variety of substituents bonded to quaternary carbons exert marked deshielding effects at antiperiplanar γ carbons. The shifts produced by methyl groups are ca. 2 ppm, while hydroxyl groups cause shifts as large as 6 ppm. These shifts are particularly clearly demonstrated by the C-19 shieldings in 5α-substituted steroids. For 9,10-disubstituted decalins, the effect is such that cis and trans isomers are not easily distinguished from their 13C spectra. These shifts contrast sharply with the corresponding effects found for substituents bonded to less highly substituted carbon skeletons.

Synthesis and X-ray study of cis and trans isomers of 6-cyano-2-oxa-10-thia-1-phosphabicyclo[4.4.0]decane-1-oxide

2000 ◽  
Vol 11 (2) ◽  
pp. 163-170 ◽  
Author(s):  
Irene L. Odinets ◽  
Natalya M. Vinogradova ◽  
Konstantin A. Lyssenko ◽  
Pavel V. Petrovskii ◽  
Tatyana A. Mastryukova
Keyword(s):  
Trans Isomers ◽  
X Ray ◽  
Cis And Trans Isomers ◽  
Cis And Trans
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