2523-37-7Relevant articles and documents
Synthesis, Crystal Structure, and Absorption Spectroscopy of a Carbazole-Dinitrofluorene Bichromophore. Identity of Ground-State Molecular Interactions in the Single Crystal and Aggregates in Solution
Brisse, Francois,Durocher, Gilles,Gauthier, Sylvain,Gravel, Denis,Marques, Rolande,et al.
, p. 6579 - 6586 (1986)
The synthesis, crystal structure, conformational analysis, and absorption spectroscopy of the bichromophore 9-(γ-(N-carbazolyl)propyl)-9-methyl-2,7-dinitrofluorene (1) are reported.The torsion angles within the propyl part of the molecule correspond to a gauche-trans-gauche-gauche conformation while the dinitrofluorene and the carbazole groups of atoms are nearly planar and are at 25.6 deg from each other.The observed conformational behavior has been analyzed with the aid of a conformational analysis program based on empirical methods, and a good agreement between calculated and crystallographic minima has been found.It is shown by the comparison of spectra in polar and nonpolar solvents that no ground-state intramolecular interaction takes place in the bichromophore.All observed spectroscopic changes are due to solute-solute intermolecular interactions or to solute-solvent intermolecular interactions.It is clearly shown that the 2,7-dinitrofluorene chromophore is responsible for all of these interactions.A new band appearing at 370 nm in a solution of the bichromophore 1 in 3-methylpentane at high concentrations or at low temperatures is assigned to aggregates by comparison with the spectrum of a single crystal.Furthermore, single-crystal data allow evaluation of the energetics of the ground and first excited electronic states of the crystal.The exciton splitting is calculated as being 887 cm-1, but this is the sum of the dipole-dipole interactions along with the charge-resonance interactions in the first excited singlet state which is mainly responsible for the 2380-cm-1 bathochromic shift observed in comparing the spectrum of the free molecule with that of the crystal.
Use of 9-methylfluorene as an indicator in the titration of common group IA and group IIA organometallic reagents
Bowen, Martina E.,Reddy Aavula, Bhasker,Mash, Eugene A.
, p. 9087 - 9088 (2002)
9-Methylfluorene was tested as an indicator in the titration of commonly used organometallic reagents. This indicator is readily prepared in three steps from fluorenone. In THF solution the deprotonated indicator is red and exhibits a sharp endpoint. The highly basic reagents secbutyllithium and tert-butyllithium can be titrated in ether solution, where the color of the deprotonated indicator is yellow.
Ylide-Substituted Phosphines with a Cyclic Ylide-Backbone: Angle Dependence of the Donor Strength
Feichtner, Kai-Stephan,Gauld, Richard M.,Gessner, Viktoria H.,Handelmann, Jens,L?ffler, Julian,Rodstein, Ilja,Schwarz, Christopher,Zur, Jana-Alina
, p. 2888 - 2900 (2021)
Ylide-substituted phosphines (YPhos) have been shown to be highly electron-rich and efficient ligands in a variety of palladium catalyzed transformations. Here, the synthesis and characterization of novel YPhos ligands containing a cyclic backbone architecture are reported. The ligands are easily synthesized from a cyclic phosphonium salt and the chlorophosphines Cy2PCl (L1) and Cy(FluMe)PCl (L2, with FluMe = 9-methylfluorenyl) and were characterized in both solution and solid states. The smaller PCy2-substituted ligand, L1, readily formed the biscoordinate L12Pd species when treated with Pd2(dba)3 and showed no activity in palladium-catalyzed amination reactions even when applied as defined palladium(II) ?3-allyl, t-Bu-indenyl, or cinnamyl precursors. Bulkier fluorenyl-substituted ligand L2 similarly was inactive, despite its ability to form the stable monophosphine complex L2·Pd(dba). Assessment of the electronic properties by experimental and computational methods revealed that L1 and L2 are considerably less electron-rich than previously synthesized YPhos ligands. This was shown to be the result of the small P-C-S bond angle, which is sterically enforced due to the cyclic nature of the backbone. Density functional theory calculations revealed that the small angle results in an increased s-character of the lone pair at the ylidic carbon atom and leads to a polarization of the C-P bond toward the carbon atom, thus decreasing the electron density at the phosphorus atom. The results demonstrate the tunability of the donor strength of YPhos ligands by modification of the ligand backbone beyond simple changes of the substitution pattern and are thus important for future ligand design, with a careful balance of many factors to be considered to achieve catalytic activity.
Atherton et al.
, p. 3041 (1979)
Dependence of stereoelectronic and charge effects on pKa values of 1,3-dithiane-derived sulfides, sulfoxides, and sulfones: An experimental and computational investigation
Süveges, Bastian D.,Podlech, Joachim
, p. 987 - 994 (2015)
The pKa values of conformationally fixed 1,3-dithianes were investigated with experimental and theoretical methods to gain an insight into the influence of the relative orientation of the acidic proton and the stabilising S=O or S-C bonds. Experimental values were determined with a modification of the spectrophotometric method using overlapping indicators developed by Bordwell; theoretical values were obtained with the proton exchange methods using DFT calculations. It turned out that stereoelectronic stabilisation is important for sulfides and sulfoxides, whereas charge effects become dominant in sulfones. Deprotonation of the equatorial proton is favoured for most of the compounds except for the equatorial/ axial bis-sulfoxide.
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Pinck,Hilbert
, p. 723 (1947)
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Synthesis of novel polyfluorene-derived task-specific ionic liquid
Zhang, Dingjun,Chen, Lei,Chen, Jianmin,Liang, Yongming,Zhou, Huidi
, p. 2609 - 2613 (2005)
The synthesis and characterization of a novel polymerizable ionic liquid derived from polyfluorene, poly[3-methyl-1-(4-(9-methyl-fluorene)-butyl)- imidazolium hexafluorophosphate] (PFIL), are described. Copyright Taylor & Francis, Inc.
Surprising sp rotameric structure of 9-methyl-9-pivaloylfluorene
Meyers, Cal Y.,Lutfi, Hisham G.,Varol, Pninit,Hou, Yuqing,Robinson, Paul D.
, p. 1468 - 1470 (2000)
Methylation of 9-lithiated ap-9-pivaloylfluorene, (I), as well as pivaloylation of 9-lithiated 9-methylfluorene provided rotationally stable sp-9-methyl-9-pivaloylfluorene, (III), C19H20O, which lies about a crystallographic mirror plane. Fluorene (I) exists exclusively in the ap configuration in solution (NMR) as well as in the crystalline state, reflecting the unfavorable interaction between the tert-butyl and fluorene-ring π electrons in the sp configuration. The existence of (III) exclusively in the sp configuration indicates that, in this case, the interaction between the tert-butyl group and the fluorene-ring π electrons provides relatively more thermodynamic stability than the steric interaction between the tert-butyl and 9-methyl groups (ap configuration).
The p: K a values of N-aryl imidazolinium salts, their higher homologues, and formamidinium salts in dimethyl sulfoxide
Cole, Marcus L.,Dunn, Michelle H.,Harper, Jason B.,Konstandaras, Nicholas,Luis, Ena T.
supporting information, p. 1910 - 1917 (2020/03/23)
A series of imidazolinium salts, their six-, seven- A nd eight-membered homologues, and the related formamidinium salts were prepared, and their pKa values were determined in DMSO at 25 °C using the bracketing indicator method. The effect of each type of structural variation on the acidity of each salt was considered, particularly noting the importance of ring size and the effect of the steric and electronic nature of the N-aryl substituents. The effect of a cyclic structure was also probed through comparing the cyclic systems with the corresponding formamidinium salts, noting the importance of conformational flexibility in the latter cases. Along with allowing choice of appropriate bases for deprotonation of these species, it is anticipated that the data presented will aid in the understanding of the nucleophilicity, and potentially catalytic efficacy, of the corresponding carbenes.
The impact of cation structure upon the acidity of triazolium salts in dimethyl sulfoxide
Konstandaras, Nicholas,Dunn, Michelle H.,Guerry, Max S.,Barnett, Christopher D.,Cole, Marcus L.,Harper, Jason B.
supporting information, p. 66 - 75 (2019/12/26)
A series of triazolium salts, selected for their varying electronic and steric properties, were prepared and their pKa values were determined in DMSO at 25 °C using the bracketing indicator method. The effect of each systematic structural variation upon the acidity of the triazolium cation has been considered, in particular examining the effects of systematically altering electronic properties, quantified through the use of Hammett σ parameters. The first pKa value for an azolium salt that generates a mesionic carbene is also reported. These new data allow for the selection of appropriate bases for the deprotonation of such triazolium salts and the potential to correlate the pKa values determined herein with the nucleophilicity of the corresponding carbenes.
