Störungstheoretische Behandlung der Chemischen Reaktivität

Hudson, R. F.

doi:10.1002/ange.19730850203

Cited by 73 publications

(14 citation statements)

References 106 publications

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“…[83c] As primary alkyl cations do not exist in the condensed phase, the exclusive formation of propyl isocyanate (86) from propyl iodide (85) can be explained by an S N 2 reaction, where the product stability term outweighs the intrinsic term in the transition state. The mixture of isopropyl cyanate (88) and isopropyl isocyanate (89) described in the second reaction in Scheme 40 reflects the result of diffusion-controlled reactions of the cyanate anion with the isopropyl cation, which can be derived from Equation (1) by using N and s N for NCO À and an estimated electrophilicity parameter of E @ 8 for iPr + .…”

Section: Cyanate Anionmentioning

confidence: 99%

Farewell to the HSAB Treatment of Ambident Reactivity

Mayr¹,

Breugst²,

Ofial³

2011

Angew Chem Int Ed

263

211

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The concept of hard and soft acids and bases (HSAB) proved to be useful for rationalizing stability constants of metal complexes. Its application to organic reactions, particularly ambident reactivity, has led to exotic blossoms. By attempting to rationalize all the observed regioselectivities by favorable soft-soft and hard-hard as well as unfavorable hard-soft interactions, older treatments of ambident reactivity, which correctly differentiated between thermodynamic and kinetic control as well as between different coordination states of ionic substrates, have been replaced. By ignoring conflicting experimental results and even referring to untraceable experimental data, the HSAB treatment of ambident reactivity has gained undeserved popularity. In this Review we demonstrate that the HSAB as well as the related Klopman-Salem model do not even correctly predict the behavior of the prototypes of ambident nucleophiles and, therefore, are rather misleading instead of useful guides. An alternative treatment of ambident reactivity based on Marcus theory will be presented.

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Section: Cyanate Anionmentioning

confidence: 99%

Farewell to the HSAB Treatment of Ambident Reactivity

Mayr¹,

Breugst²,

Ofial³

2011

Angew Chem Int Ed

263

211

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“…Finally, H-Ala-Leu-Ala-Lys-LeuGly-Gly-H (9) (6 equivalents) was coupled to the template 7 in neat buffer. Both reagents were fully soluble and after 6 h the product, a 2.9 kDa carbopeptide (12), was isolated by semi-prep. HPLC in 64% yield ( Figure 5).…”

Section: Preparation Of Carbopeptides By Oxime Ligationmentioning

confidence: 99%

“…other than amide) bond at the site of ligation, this includes oxime and hydrazone ligations, developed by Rose [11], in which aminooxy or hydrazine nucleophiles react with aldehydes or ketones. Due to the h-effect [12] of the neighboring heteroatom, aminooxy derivatives are weak bases but reactive nucleophiles towards carbonyl groups at an acidic pH range of 4-5.5 where basic side-chain nucleophiles are protonated. With aldehydes and ketones oximes are formed which are stable under neutral to mildly acidic conditions [13].…”

Section: Introductionmentioning

confidence: 99%

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Carbopeptides: chemoselective ligation of peptide aldehydes to an aminooxy-functionalized D-galactose template

Brask

Jensen

2000

J. Peptide Sci.

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“…We used the General Theory of Perturbation Limited to the Frontier Molecular Orbitals. [34][35][36][37][38] The geometry of the 4-(4-chlorophenyl)pyrimidinium benzoyl methylide 5a (for the energetically most favoured geometry, the heat of formation is ∆H= 63.174 kcal/mol), the atomic charges, the coefficients of the atomic orbitals, and the values of the energies of the frontier molecular orbitals ( An analysis of the data from Table 2 leads to the following conclusions: -the ylide carbanion center, C-7, has a negative atomic charge, less than unity, but significant; -the ylide nitrogen atom, N-1, has a positive atomic charge, less than unity, significant but smaller (in absolute value) than the ylide carbanion; -the α-endocyclic carbon atoms, C-2 and C-6, have small negative atomic charges, both being less than unity. Table 2.…”

Section: Methodsmentioning

confidence: 99%

4-(4-Chloro-phenyl)-pyrimidinium ylides. 1. Structure, stability, reactivity

Moldoveanu¹,

Mangalagiu²,

Caprosu³

et al. 2004

Arkivoc

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In this paper we present a theoretical and experimental study concerning the structure, stability, and reactivity of 4-(4-chlorophenyl)pyrimidinium ylides. 4-(4-Chlorophenyl)-pyrimidinium ylides are relatively stable compounds, their stability varying with the nature of the ylide carbanion substituent. The stronger the electron-withdrawing effect of these substituents, the more the anionic charge is delocalized, and therefore the higher their stability. The experimental and quantum chemical calculations confirm this hypothesis and are in accordance with each other. The electronic absorption spectra of 4-(4-chlorophenyl)-pyrimidinium 4-X-benzoyl methylides can be assigned to an intramolecular charge transfer band. The quantum chemical calculations show the possibility to use pyrimidinium ylides as nucleophilic reagents as well as 1,3-dipoles in reaction with appropriate reagents. The influence of microwave irradiation for the synthesis of azinium salts was also studied. The reaction of 4-(4-chlorophenyl)pyrimidine with an organic haloalkane shows a remarkable rate acceleration under microwave irradiation and allows a general and facile synthesis of azinium salts. A comparative study of microwave and classical conditions (use of solvents) has been done.

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Störungstheoretische Behandlung der Chemischen Reaktivität

Cited by 73 publications

References 106 publications

Farewell to the HSAB Treatment of Ambident Reactivity

Farewell to the HSAB Treatment of Ambident Reactivity

Carbopeptides: chemoselective ligation of peptide aldehydes to an aminooxy-functionalized D-galactose template

4-(4-Chloro-phenyl)-pyrimidinium ylides. 1. Structure, stability, reactivity

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