Trennung und Äquilibrierung zweier <i>syn‐anti</i>‐isomerer Hydrazone

Krebs, Adolf; Kimling, Horst

doi:10.1002/jlac.19707400114

Cited by 12 publications

(17 citation statements)

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“…The unusually small coupling constant lJCH 152 Hz at the olefinic carbon atoms again points to a larger-than-average C=C-C bond angle [ 131. A correlation between 13C chemical shifts of acetylenic carbon atoms and the deviation Aa from linearity of the C-C-C bond angles in strained cycloalkynes was noted by Krebs & Kimling[15]. By comparison with their data and those of 2 ( d a 21", 6 (-C-) 95.8 ppm[4]) we estimate d a (3) as 25 to 30" on the basis of the observed shift of 6 (-C=) 100.4ppm.…”

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confidence: 69%

“…The products obtained by reacting 3 with various substrates are shown in Scheme 4. All ground-state reactions are initiated by attack at the triple bond and have many analogies in the chemistry of strained cycloalkynes [ l ] [4] [15]. Where a comparison is possible, the reactivity of 3 is found to be considerably greater than that of 1 or 2.…”

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confidence: 99%

“…The solvent was evaporated and the residue was chromatographed on silica with chloroform. The orange eluate was collected and recrystallized from carbon tetrachloride to yield 20 mg of bis(cycloocta-1,5-dieno[d,d]-2,2'-bi(1,3-dithiolylidene) (15) as red crystals, m.p. 204".…”

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confidence: 99%

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Cyclooct‐1‐en‐5‐yne. Preparation, spectroscopic characteristics and chemical reactivity

Leupin

Wirz

1978

Helvetica Chimica Acta

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Cyclooct-1-en-5-yne (3) has been obtained as an isolable, but highly reactive hydrocarbon by oxidation of cyclooct-5-ene-1,2-dihydrazone with lead tetraacetate (Scheme 2). Information regarding the structure and conformational mobility of 3 has been gained from the analysis of its 'Hand I3C-NMR. spectra and was found to agree with the results of force field calculations. Photolysis (206 nm) of 3 in solution has induced cleavage to butatriene and butadiene. The first band in the photoelectron spectrum of 3 (I, 9.10 eV) is attributed to ionization from a rather delocalized orbital with predominant weight of the double bond p-AO's. Nevertheless, the high reactivity of 3 stems from the strained triple bond as evidenced by the reaction products obtained by pyrolysis, oxidation, Diels-A lder addition, and 1,3-dipolar addition (Scheme 4).

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confidence: 69%

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confidence: 99%

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Cyclooct‐1‐en‐5‐yne. Preparation, spectroscopic characteristics and chemical reactivity

Leupin

Wirz

1978

Helvetica Chimica Acta

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“…Krebs and Kimling separated and studied the interconversion of the E-and Z-isomers of hydrazone 1. 23 They found the values of D { G 0 are 32.0 and 32.2 kcal/mol in benzonitrile for the forward and reverse reactions, respectively. The hydrazone 2 has a value of D { G 0 about 24-25 kcal/mol.…”

Section: Resultsmentioning

confidence: 96%

Gibbs energy of activation for thermal isomerization of (1Z)‐acetaldehyde hydrazone and (1Z)‐acetaldehyde N,N‐dimethylhydrazone by Gaussian‐4 theory and CCSD(T)/CBS computations

2009

J Comput Chem

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In this article, we examined the Gibbs energy of activation for the Z/E thermal isomerization reaction of (1Z)-acetaldehyde hydrazone and (1Z)-acetaldehyde N,N-dimethylhydrazone, at 298.15 K in the solvent of cyclohexane. We carried out computations employing both the Gaussian-4 (G4) theory and the coupled cluster method using both single and double substitutions and triple excitations noniteratively, CCSD(T). The CCSD(T) energy is extrapolated to the complete basis set (CBS). We compared the calculated results to the available experimental observation. It appeared that both G4 and CCSD(T)/CBS computations overestimated the experimental value by as much as about 6 and 12 kcal/mol in the present two cases. We discussed possible sources of error and proposed the experimental kinetic data could be questionable.

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“…Krebs and co-workers have synthesized numerous cycloheptyne derivatives of the general structure 74 [12]; most of them are more stable than 72. For example the thio ether (74, X = S) shows no tendency to di-or oligomerization even at 140 °C [61]. Because of the stability of the sulfur compound it was possible to determine its molecular structure by electron diffraction; with 145.8° for the C C-C angle the deformation is about 12.7° higher than that observed for cyclooctyne (see below) [62].…”

Section: Cycloheptyne and Its Derivativesmentioning

confidence: 99%

Angle‐Strained Cycloalkynes

Hopf¹,

Grunenberg²

2009

Strained Hydrocarbons

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IntroductionAccording to the sp-hybridization model, the carbon-carbon triple bond possesses a linear structure, and indeed, many alkynes fulfill this prediction. High level ab initio calculations [1] of isolated alkyne molecules, as well as gas phase electron diffraction experiments [2] reveal their linear minimum structure. On the other hand, given that the C C-R bending force constant becomes intrinsically smaller for substituted alkynes and polyynes, crystal packing effects may lead to deviations from strictly linear geometries [3]. From a dynamic point of view even in the case of acetylene one has to include the -albeit reduced -flexibility of the carboncarbon triple bond in order to describe, for example, the vinylidene acetylene rearrangement (see below) [4]. Further, the linear sp-hybrid picture only holds true for the electronic ground state. Cis-and trans-bent configurations are known in the case of low-lying electronic states [5]. Nevertheless, many alkynes correspond to the prediction of linearity due to the sp-hybrid model, and we have collected a selection of typical examples, reaching from the parent compound acetylene 1 via a few alkyl 2-4 and aryl acetylenes 5-7 to a functionalized acetylene, dimethyl acetylenedicarboxylate 8, in Scheme 7.1, together with the appropriate references [1, 2, 6-11], all dating from the recent literature.The easiest way to distort a triple bond is to incorporate it into a sufficiently small ring structure. The question, of course, is what this ring size is, and from what ring size on the respective cycloalkynes can we isolate compounds, that can be worked with under normal laboratory conditions [12]. Rather than using the nonspecific term 'distorted cycloalkyne' Krebs [12] prefers to speak of 'angle-strained cycloalkynes'. Since it is easier to deform a C C-C arrangement than its more hydrogenated olefinic and saturated analogs, relatively large angle deformations are possible in cycloalkynes without significant changes in energy. Krebs arbitrarily considers all cycloalkynes in which the C C-C angle is deformed by more than 10° as angle-strained [12]. Accepting this definition, the stable cyclononyne (see below) is an angle-strained cycloalkyne, whereas cyclodecyne is not.

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Trennung und Äquilibrierung zweier syn‐anti‐isomerer Hydrazone

Cited by 12 publications

References 11 publications

Cyclooct‐1‐en‐5‐yne. Preparation, spectroscopic characteristics and chemical reactivity

Cyclooct‐1‐en‐5‐yne. Preparation, spectroscopic characteristics and chemical reactivity

Gibbs energy of activation for thermal isomerization of (1Z)‐acetaldehyde hydrazone and (1Z)‐acetaldehyde N,N‐dimethylhydrazone by Gaussian‐4 theory and CCSD(T)/CBS computations

Angle‐Strained Cycloalkynes

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