Kritik der Medien

Göttlich, Udo

doi:10.1007/978-3-322-95652-1

Cited by 27 publications

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“…This has been tested with a number of model compounds (Scheme 12). 16 As can be seen from the coupling constants, the effects caused by a single sp 2 -hybridized substituent are rather small; DG values which affect the conformer equilibrium, do not exceed ca. 0.5 kcal mol 21 .…”

Section: End-group Control Of Conformationmentioning

confidence: 94%

“…Hence, compound 20 should have only one low energy conformation, the one shown, a fact that is reflected in the strong difference of the coupling constants recorded for 20. 16 This effect can be used to selectively exert local conformation control in more extended molecular backbones such as 21 (Scheme 11). 17 sp 2 -Hybridized end groups, such as vinyl, phenyl and methoxycarbonyl are, on the other hand, slimmer than a CH 2 R group.…”

Section: End-group Control Of Conformationmentioning

confidence: 99%

“…1 The effects that may be attained by multiple substitution of a chain with sp 2 -hybridized substituents are less striking. Nevertheless, the coupling constants recorded for 25 16 indicate that about 50% of the total conformer population has a central g 2 ttg + conformation (Scheme 15).…”

Section: Conformation Designmentioning

confidence: 99%

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Open chain compounds with preferred conformations1

Göttlich¹,

Kahrs²,

Krüger³

et al. 1997

Chem. Commun.

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Section: End-group Control Of Conformationmentioning

confidence: 94%

Section: End-group Control Of Conformationmentioning

confidence: 99%

See 1 more Smart Citation

Open chain compounds with preferred conformations1

Göttlich¹,

Kahrs²,

Krüger³

et al. 1997

Chem. Commun.

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“…While the conformational properties of 22 have not been studied yet experimentally, data are available for the related diol derivative 23. [16] Analysis of the 1 H NMR coupling constants suggests that in 23 the conformation shown in 23 a is populated with a 7:1 preference in segment A and a 7:1 preference in segment B. Moreover, the conformation 23 a is the one present in crystalline 23.…”

Section: Inductor Groups Based On Methylcyclohexane Skeletonsmentioning

confidence: 97%

Conformation Design of Hydrocarbon Backbones: A Modular Approach

et al. 1998

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IntroductionUnbranched hydrocarbon chains have an enormous number of populated low-energy conformers. [2, 3] This number can be reduced by substituents that introduce steric strain in certain conformers. This is achieved most effectively [4] if these substituents create destabilizing syn-pentane interactions, [5] which add 7 ± 9 kJ mol À1 to the energy of a given conformer. The population of the remaining low-energy conformers is thereby increased (see Scheme 1).We are interested in defining substitution patterns on a hydrocarbon chain that would thus destabilize all but one conformer, which would remain free of syn-pentane inter- actions. This conformer would then be the only low-energy conformer and should be highly preferentially populated. If this conformer is populated to b 80 %, we call the compound or a particular segment of a compound monoconformational. [6,7] As a first step, we want to identify small segments of a hydrocarbon backbone, segments that, by virtue of their substituent pattern, have only a single low-energy conformation. As a next step we shall consider how these segments may be connected with one another to result in larger hydrocarbon backbones, which should ideally maintain the property of preferentially populating a single conformation. Discussion 1. Basic types of monoconformational skeletons: The smallest hydrocarbon segment to be considered is 2,3-dimethylbutane (2).[8] When rotating about the central 2,3-bond, 2 has three rotamers that are located at energy minima, 2 a ± c (Scheme 2). Rotamer 2 c is the lowest energy conformer. Energies of 2 a and 2 b are calculated to be slightly (ca. 1.5 kJ mol À1 ) higher, because one of the methyl groups is exposed to a double gauche interaction with two other methyl groups. To render the 2,3-dimethylbutane backbone monoconformational, two out of the three conformations of 2 have to be destabilized selectively, for example by introducing syn-pentane interactions. For instance, if it were possible to place an additional methyl group at C1 of 2, with the methyl group kept in an antiperiplanar orientation to the neighboring C2 methyl group, that is, 3, syn-pentane interactions would be created in conformers 3 b and 3 c, but not in 3 a. Likewise, if it were possible to fix the additional methyl group at C1 of 2 in a Conformation Design of Hydrocarbon Backbones: A Modular Approach** Reinhard W. Hoffmann,* Martin Stahl, Ulrich Schopfer, and Gernot Frenking* Abstract: A modular approach towards a conformation design of hydrocarbon backbones is described. The idea is to attach substituents (e.g., methyl branches) to a hydrocarbon backbone in such a manner that they create destabilizing syn-pentane interactions in all but one diamond-lattice backbone conformation. This creates a substantial (b 7 kJ mol À1 ) energy gap between the lowest energy conformer and the higher energy conformers. In consequence, the lowest energy conformer will be populated to a high extent (e.g., b 80 %). Small hydrocarbon modules that fulfil this requirement have been identified...

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Ruhrmann

Nieland

1997

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Kritik der Medien

Cited by 27 publications

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Open chain compounds with preferred conformations1

Open chain compounds with preferred conformations1

Conformation Design of Hydrocarbon Backbones: A Modular Approach

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