Molecular Complexes, 14. Isomeric Arene Complexes of Caffeine and 1,3,7,9-Tetramethyluric Acid Detected with Toluene. Polar Interactions Inverted with Hexafluorobenzene
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Helmut Stamm
,
Hannelore Jäkel
Stacking of an arene D on caffeine (1) near 7-Me and 8-H is known (1H NMR shifts, CCl4, AUS concept) to yield the same association constant K for each signal of 1. Toluene (T) and 1 now yielded the same K from 7-Me and 8-H while K from 1-Me (and 3-Me) is smaller indicating a minor stacking centre near N-1 that forms both 1T and 1T2; this 1T2 disturbs computations of K. The main stacking centre forms no 1T2 since its 1T is stabilized by dipole-dipole interaction. Diphenylmethane Dp, a substituted T that cannot form a dimer of type T2, does not form 1Dp2. Ethyl of 1-ethyltheobromine (2) is proven to stand perpendicular so that the above minor complex can only arise on one face of 2 halving Kminor and making the disturbance of computations by 2T2 insignificant; apart from this minor 2T there are cis-trans isomers of the main complex. Stacking of 1 and 2 with larger arenes is discussed in terms of relative molecular sizes under consideration of the perpendicularly placed ethyl group of 2. Stacking of D near N-3 and N-9 of 1,3,7,9-tetramethyluric acid (4) is known. 4 and T now provided K = 0.218 l mol−1 from 3-Me and 9-Me but K = 0.157 l mol−1 from 1-Me and 7-Me. This and the complex induced shifts IK indicate formation of stacking 4T + 4T2 and of two edge-on 4T standing on 3-Me and 9-Me under dipole-dipole interaction with a neighbouring oxygen. The oxygens of 4 (and probably of 1, too) form edge-on complexes with hexafluorobenzene; this underlines the importance of polar effects.
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- Synthesis of Spacered Nucleoside Analogues Comprising a Difluorocyclopropane Moiety
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Articles in the same Issue
- ERRATUM
- Asymmetric Catalysis, 154 [1]. New 1,1’-Binaphthyl Ligands for Enantioselective Catalysis
- Ternary Gallides REMgGa (RE = Y, La, Pr, Nd, Sm–Tm, Lu) – Synthesis and Crystal Chemistry
- Organometallic Compounds of the Lanthanides 169. Lanthanidocene Complexes Containing Chiral Nitrogen-Functionalized Cyclopentadienyl Ligands
- Structural Features of a Sulfur-Containing Group 4 Metalla[11]-crown-4 Derivative
- Synthesis of Cyclopropanoid Nucleoside Analogues Possessing a Flexible Side Chain
- Synthesis of Spacered Nucleoside Analogues Comprising a Difluorocyclopropane Moiety
- Synthesis of Some New Chiral Tricyclic and Macrocyclic Pyridine Derivatives as Antimicrobial Agents
- Molecular Complexes, 14. Isomeric Arene Complexes of Caffeine and 1,3,7,9-Tetramethyluric Acid Detected with Toluene. Polar Interactions Inverted with Hexafluorobenzene
- Synthesis and One-Electron Oxidation Chemistry of Stable β,β-Dimesityl Enols with Heteroaryl Substituents
- α-Dicarbonylmonohydrazone und ihre Acylderivate als Nucleophile und Nachbargruppen/α-Dicarbonylmonohydrazones and their Acylderivatives as Nucleophiles and Neighbouring Groups
- Synthesis of Some New (Nα-Dipicolinoyl)-bis-L-leucyl-DL-norvalyl Linear tetra and Cyclic octa Bridged Peptides as New Antiinflammatory Agents
- Synthesis, Characterisation and Structural Studies of [Zn(phen)3][Fe(CN)5(NO)]·2H2O·0.25MeOH and [(bipy)2(H2O)Zn(μ-NC)Fe(CN)4(NO)]·0.5H2O
- Photolysis of Naphthol Green B in Aqueous Solution. Photoreduction of Fe(III) Induced by Ligand-to-Metal Charge Transfer Excitation
- Crystal Structure of B-Type Tm2Si2O7 (≡Tm4[Si3O10][SiO4])
- Neue Strukturverfeinerung und Eigenschaften von Cr3C2/Structure Refinement and Properties of Cr3C2
