Molecular complexes. Part 12.1 Dimeric toluene, torsional vibrations, dipoles and isomeric complexes in 1H NMR studies of weak arene complexes. Temperature dependence of CH signals

Stamm, H.; Strumm, Hanns-Otto; Loebel, Karl-Heinz; Jäckel, Hannelore; Hoffmanns, Ulrich; Bethke, Sabine; Schilling, Gerhard

doi:10.1039/b105946g

Cited by 4 publications

(14 citation statements)

References 22 publications

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“…The AUS method subsequently showed with 17 arenes [16,17] that only 1:1 complexes are formed whose complex centre is near 7-Me and 8-H. This centre is in accord with the direction of the dipole moment of 1 [18] as well as with the formation of an intermolecular hydrogen bond from =CH (position 8) to a carbonyl oxygen both in the crystal [19] and in CD 3 COCD 3 [5]. The same centre was found (5 arenes) for complexes of 1-ethyltheobromine (2, Fig.…”

Section: Introductionmentioning

confidence: 65%

“…This conformation is unambigously corroborated by the temperature dependence (cf. [5]) of signals. Cooling (+25 • C to −15 • C) a solution of 2 in CCl 4 makes signals go downfield by 0.044 ppm (8-H), 0.021 ppm (7-Me), 0.006 ppm (3-Me) and upfield by 0.021 ppm (CH 2 ) and 0.0006 ppm (C-Me).…”

Section: Resultsmentioning

confidence: 98%

“…AT 2 might be considered to arise from A and the toluene dimer T 2 , a stacking dimer with antiparallel T dipoles [12]. Isomeric complexes with T are detectable when one of them profits from a dipoledipole attraction in AT that prevents formation of the corresponding AT 2 (stacking of three dipoles) [5].…”

Section: Introductionmentioning

confidence: 99%

“…The parameters refer to all complexes if more than one is formed. For concise descriptions of method and parameters see [5,7]. The computer program CA-AUS based on the method of Cresswell and Allred [8] is less sensitive to experimental error than Sc-AUS based on the method of Scatchard [9].…”

Section: Introductionmentioning

confidence: 99%

“…Value and power of the method are shown e. g. by detecting edge-on complexing through a very large IK when a stacking interface is too small [10] or by the detection of hindered torsional vibrations in stacking AD [5] and Brought to you by | California Institute of Technology Authenticated Download Date | 9/28/15 4:45 PM Table 1. Parameters for complexation of 1 (caffeine) and T (d 8 -toluene) a ; rounded parameters for complexations of 1 b and 2 c with B (d 6 -benzene), T, Dp (diphenylmethane), Bp (biphenyl), N (d 8 -naphthalene), P (phenanthrene) and Fa (fluoranthene).…”

Section: Introductionmentioning

confidence: 99%

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Molecular Complexes, 14. Isomeric Arene Complexes of Caffeine and 1,3,7,9-Tetramethyluric Acid Detected with Toluene. Polar Interactions Inverted with Hexafluorobenzene

Stamm

Jäkel

Stafe

2003

Zeitschrift Für Naturforschung B

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Stacking of an arene D on caffeine (1) near 7-Me and 8-H is known ( 1 H NMR shifts, CCl 4 , 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 1T 2 ; this 1T 2 disturbs computations of K. The main stacking centre forms no 1T 2 since its 1T is stabilized by dipole-dipole interaction. Diphenylmethane Dp, a substituted T that cannot form a dimer of type T 2 , does not form 1Dp 2 . 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 K minor and making the disturbance of computations by 2T 2 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 + 4T 2 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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Section: Introductionmentioning

confidence: 65%

Section: Resultsmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Molecular Complexes, 14. Isomeric Arene Complexes of Caffeine and 1,3,7,9-Tetramethyluric Acid Detected with Toluene. Polar Interactions Inverted with Hexafluorobenzene

Stamm

Jäkel

Stafe

2003

Zeitschrift Für Naturforschung B

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Effect of Reaction Parameters on the Synthesis of 5-Arylidene Barbituric Acid Derivatives in Ball Mills

Schmidt

Burmeister

Baláž

et al. 2015

Org. Process Res. Dev.

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The influence of crucial reaction parameters on Knoevenagel condensation in planetary ball mills was investigated. Rotation frequency (ν rot ), milling ball diameter (d MB ), milling ball filling degree (Φ MB ), and beaker size had obvious influences on yield. It was found that higher ν rot , lower d MB , milling beakers with larger diameter, and a Φ MB of ∼0.3 are advantageous for the reaction. Furthermore, the influence of the type of mill was investigated, including reactions performed in different planetary and mixer ball mills, in a stirred media mill, and with a mortar mill. Comparisons with the other solvent-free synthetic routes showed that ball milling is an effective way of performing the reaction with low energy intensity. ■ INTRODUCTIONThe use of mechanical stress for the accomplishment of mechanochemical reactions is now an established field of research represented by a huge number of reactions in different fields of organic, inorganic, and organometallic chemistry and materials science. 1 In all cases, mechanical stress is provided to the reactants, whereby the energy input can be realized in different ways. The easiest but imprecise way is to use a mortar and pestle. 2 Results that are more reliable can be obtained with different types of ball mills, such as planetary (PBMs) or mixer ball mills (MBMs). The results of organic reactions in ball mills are subject to several influencing parameters, especially the influence of rotation frequency (ν rot ), milling time (t), and number of milling balls (n MB ). 3 Although a large number of synthesis protocols have been published, parameters such as the milling ball diameter (d MB ) 3c,d,4 and beaker size 5 have received less attention. Furthermore, comparative studies on reactions in different types of mills are rare. 2,6 However, the kind of mill utilized can strongly influence the outcome of a reaction. For example, Schneider et al. investigated the Suzuki−Miyaura reaction in two types of PBMs and one MBM. 2 The reaction proceeded well in the PBMs at 300 min −1 , whereas in the MBM at the same frequency only low yields were observed. Wang and co-workers investigated pinacol couplings in an MBM and a mortar mill (MM). 6a Although mechanical energy is supplied in both mill types, higher yields of the pinacol coupling product were obtained in an MM.We have recently investigated the influence of several reaction parameters on the yield of a Knoevenagel condensation of vanillin (1a) and barbituric acid (2a) (Scheme 1) in a planetary ball mill aiming to close this knowledge gap, 5 including questions regarding the influence of beaker size, geometry, and the way the mechanical energy is provided. To this end, Knoevenagel condensation was performed using various tools for allocating mechanical stress.To investigate the influence of different milling and grinding apparatuses, three different types of PBMs, an MBM, a stirred media mill (SMM), an MM, and a mortar and pestle were used. The main differences between the PBMs are the diameter of the main disc (d MD ),...

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New insights into prediction of weak π–π complex association through proton-nuclear magnetic resonance analysis

2020

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For analysis of weak π–π complexes proton-nuclear magnetic resonance (proton-NMR) simultaneously provides information of stacking configurations and association constants $$\left( K \right)$$ K However, an apparent issue for this approach is inconsistent/impossible constant estimation which often leads to unreasonable interpretation for π–π complexation. Whether or not this proton-dependent constant variation could be attributed to simple experimental uncertainties or to more sophisticated additional unspecific shielding effects (AUS effects) was addressed by means of hypothesis tests using a robust bootstrap technique in this report. Our analysis shows the significance of AUS effects on such variation in constant estimation. A following study using numeric simulation further reveals the variation patterns induced by AUS effects and concludes that the largest $$K$$ K among the obtained $$K$$ K estimates of a complex is considered as the best estimate of $$K$$ K due to minimum deviation from the true value of K and the multiple $$K$$ K estimates of a π–π complex could provide preferable inferences for complex geometries.

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Molecular complexes. Part 12.1 Dimeric toluene, torsional vibrations, dipoles and isomeric complexes in 1H NMR studies of weak arene complexes. Temperature dependence of CH signals

Cited by 4 publications

References 22 publications

Molecular Complexes, 14. Isomeric Arene Complexes of Caffeine and 1,3,7,9-Tetramethyluric Acid Detected with Toluene. Polar Interactions Inverted with Hexafluorobenzene

Molecular Complexes, 14. Isomeric Arene Complexes of Caffeine and 1,3,7,9-Tetramethyluric Acid Detected with Toluene. Polar Interactions Inverted with Hexafluorobenzene

Effect of Reaction Parameters on the Synthesis of 5-Arylidene Barbituric Acid Derivatives in Ball Mills

New insights into prediction of weak π–π complex association through proton-nuclear magnetic resonance analysis

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