The influence of substituents on the geometry of the cyclopropane ring. I. The crystal and molecular structure of cyanocyclopropane at −85°C. Film and diffractometer measurements

Kiers, C. Th.; Boer, J. S. A. M. de; Heijdenrijk, D.; Stam, C. H.; Schenk, H.

doi:10.1002/recl.19851040103

Cited by 13 publications

(3 citation statements)

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“…A second test concerned the powderdiffractogram of CPCN (Kiers, de Boer, Heijdenrijk, Stam and Schenk, 1985) generated from single-crystal data (Jansen, Peschar and Schenk, 1992a). It was shown that many of the normalized structure-factors, obtained by the least-squares fitting procedure LSQPROF, which were indicated to be strong or weak, are not strong respectively weak at all (Jansen, Peschar and Schenk, 1992b).…”

Section: Preliminary Test Resultsmentioning

confidence: 99%

“…Figure 1 shows the differences of the fitted and true normalized structure factors of CPCN (Kiers, de Boer, Heijdenrijk, Stam and Schenk, 1985) after the application of the Direct Intensity Fitting technique as a function of the interpeak distance in units of the halfwidth of the peaks. It can be seen that the intensities become less reliable if the interpeak distance decreases.…”

Section: Weighting Scheme For Intensitiesmentioning

confidence: 99%

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Application of Direct Methods to powder data. A weighting scheme for intensities in the optimal symbolic addition program SIMPEL88

Jansen¹,

Peschar²,

Schenk³

1993

Zeitschrift Für Kristallographie - Crystalline Materials

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Application of Direct Methods to reflection intensities obtained by powder diffraction is often obstructed by the fact that not all intensities are reliable. In this paper a weighting scheme is proposed to overcome this problem. The scheme is implemented in the Direct Methods program SIMPEL88 in such a way that phase relations containing overlapping reflections are less probable than they would have been containing very reliable reflections only. Preliminary test results show that this way of tackling the problem is very promising.Brought to you by | provisional account Unauthenticated Download Date | 6/26/15 8:05 AM

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Section: Preliminary Test Resultsmentioning

confidence: 99%

Section: Weighting Scheme For Intensitiesmentioning

confidence: 99%

Application of Direct Methods to powder data. A weighting scheme for intensities in the optimal symbolic addition program SIMPEL88

Jansen¹,

Peschar²,

Schenk³

1993

Zeitschrift Für Kristallographie - Crystalline Materials

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“…In addition to their ability to interact with adjacent π systems, cyclopropanes function as effective donors when activated by adjacent low‐lying empty orbitals: this can be rationalized by considering the Walsh orbitals 6. 7 Striking manifestations of the electron‐donating aptitude of cyclopropanes include: 1) the unusual thermodynamic stability of the cyclopropylcarbinyl cation,8 and 2) the bond‐length asymmetry of cyclopropanecarbonitirile (Δd (distal−vicinal) =0.033 Å) as a consequence of hyperconjugation 9. 10 Of particular pertinence to this study is the latter observation.…”

Section: Methodsmentioning

confidence: 92%

Cyclopropyl Iminium Activation: Reactivity Umpolung in Enantioselective Organocatalytic Reaction Design

2011

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The intrinsic donor-acceptor reactivity pattern of conjugated, unsaturated carbonyl compounds predictably alternates along the carbon chain (Scheme 1). Consequently, electrophiles are predisposed to react at the a (d 2 ) and g (d 4 ) donor positions, whereas nucleophiles add to the b (a 3 ) and d (a 5 ) acceptor positions. Direct inversion of this inherent selectivity is known as reactivity umpolung, [1] and often provides a platform for the development of novel transformations. While various activation modes that allow for a (a 2 /d 2 ), b (a 3 ), g (d 4 ), and e (d 6 ) functionalization have been reported through secondary amine organocatalysis, [2] umpolung strategies remain elusive outwith the confines of SOMO activation [2b] and processes mediated by N-heterocyclic carbenes (NHCs). [3,4] Because pyrrolidine-and imidazolidinone-based organocatalysts require carbonyl substrates to generate the transient intermediates that are central for catalysis, the substrate scope is limited to aldehydes and ketones with varying degrees of unsaturation. With a view to extending the substrate scope of secondary-amine-catalyzed processes, and providing an entry point into the design of homologous variants of addition reactions to a,b-unsaturated iminium ions, we began exploring the reactivity of cyclopropane carbaldehydes.Cyclopropane behaviour has striking parallels with that of olefins.[5] In addition to their ability to interact with adjacent p systems, cyclopropanes function as effective donors when activated by adjacent low-lying empty orbitals: this can be rationalized by considering the Walsh orbitals. [6,7] Striking manifestations of the electron-donating aptitude of cyclopropanes include: 1) the unusual thermodynamic stability of the cyclopropylcarbinyl cation, [8] and 2) the bond-length asymmetry of cyclopropanecarbonitirile (Dd (distalÀvicinal) = 0.033 ) as a consequence of hyperconjugation. [9,10] Of particular pertinence to this study is the latter observation. It was envisaged that the well described conjugation between a cyclopropane moiety and polar multiple bonds might form the basis of an activation strategy involving cyclopropyl iminium salts. Indeed, Wang and co-workers have described that the nucleophilic addition of benzenethiols to cyclopropanecarbaldehydes can be catalyzed by proline.[11] The similarities in bonding between this species and that of conventional a,b-unsaturated iminium ions, together with the expected interaction of the cyclopropyl moiety with the conjugated iminium functionality, motivated us to investigate the reactivity of cyclopropane carbaldehydes [12] upon unification with secondary amines (Scheme 2). Formally, nucleophilic addition to the transient cyclopropyl iminium species would constitute a formal umpolung of the g-position of a dienamine;[2c] d 4 !a 4 (Scheme 1). Moreover, by intercepting the transient enamine with an electrophile, this strategy would give an unprecedented method for the organocatalytic formation of 1,3-difunctionalized products in a single operation (Sche...

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Structural Chemistry of Cyclopropane Derivatives

Rozsondai

2009

Patai's Chemistry of Functional Groups

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Introduction Cyclopropane Substituted Cyclopropanes Cyclopropylidenes Cyclopropenes Cyclopropenylidenes and Related Systems Cyclopropane Rings in Polycyclic Systems Acknowledgements

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The influence of substituents on the geometry of the cyclopropane ring. I. The crystal and molecular structure of cyanocyclopropane at −85°C. Film and diffractometer measurements

Cited by 13 publications

References 9 publications

Application of Direct Methods to powder data. A weighting scheme for intensities in the optimal symbolic addition program SIMPEL88

Application of Direct Methods to powder data. A weighting scheme for intensities in the optimal symbolic addition program SIMPEL88

Cyclopropyl Iminium Activation: Reactivity Umpolung in Enantioselective Organocatalytic Reaction Design

Structural Chemistry of Cyclopropane Derivatives

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