Tautomerism and the maximum hardness principle

2006 ◽  
Vol 106 (8) ◽  
pp. 1723-1735 ◽  
Author(s):  
Yi-Liang Zhang ◽  
Zhong-Zhi Yang
Keyword(s):  
Maximum Hardness ◽  
Maximum Hardness Principle

Electronegativity and redox reactions

2016 ◽  
Vol 18 (32) ◽  
pp. 22235-22243 ◽  
Author(s):  
Ramón Alain Miranda-Quintana ◽  
Marco Martínez González ◽  
Paul W. Ayers
Keyword(s):  
Redox Reactions ◽  
Oxidation Potential ◽  
Maximum Hardness ◽  
Maximum Hardness Principle

Using the maximum hardness principle, we show that the oxidation potential of a molecule increases as its electronegativity increases and also increases as its electronegativity in its oxidized state increases.

Synthesis, Structural Preference and Catalytic Activity of Neutral and Cationic Methylpalladium(II) Complexes Containing N-Arylpyridine-2-carbaldimine Chelating Ligands

2002 ◽  
Vol 67 (8) ◽  
pp. 1200-1214 ◽  
Author(s):  
Ana Arnaiz ◽  
Gabriel García-Herbosa ◽  
José V. Cuevas ◽  
Olivier Lavastre ◽  
Caroline Hillairet ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Chelating Ligands ◽  
Maximum Hardness ◽  
Neutral Complex ◽  
Synthesis And Crystal Structure ◽  
Square Planar ◽  
Square Planar Complexes ◽  
Alkene Oligomerization ◽  
Maximum Hardness Principle ◽  
Rule Out

The syntheses and structures of neutral complexes [PdCl(Py-2-CH=NAr)(Me)] (Ar = 4-MeC6H4, 4-MeOC6H4, 4-CF3C6H4) and cationic complexes [Pd(Py-2-CH=NAr)(Me)(MeCN)]SbF6 (Ar = 4-MeC6H4, 4-MeOC6H4, 4-CF3C6H4) are described. The preference for the trans-isomers in the cationic complexes and for the cis-isomers in the neutral complexes is discussed on the basis of electronic arguments and supported by DFT calculations. The observed preference seems to follow the maximum hardness principle (MHP) introduced by Pearson. On the basis of the application of this principle to square planar complexes of palladium(II) and platinum(II) we propose the trans choice, which means that the hardest ligand arranges trans to the softest one. The synthesis and crystal structure of the related neutral complex trans-[Pd(CF3COO)(Py-2-CH=NC6H4-4-OMe)(Me)] is also described and allows to rule out the charge of the complex as the cause of isomeric preference. We also report our preliminary studies dealing with the catalytic activity of the cationic complexes in alkene oligomerization and copolymerization with CO.

AN ANALYSIS OF THE REGIOSELECTIVITY IN HETERO DIELS–ALDER REACTIONS USING DFT-BASED REACTIVITY INDEXES

2006 ◽  
Vol 05 (02) ◽  
pp. 197-206 ◽  
Author(s):  
H. CHEMOURI ◽  
S. M. MEKELLECHE
Keyword(s):  
Diels Alder ◽  
Maximum Hardness ◽  
Activation Barriers ◽  
Reactivity Indexes ◽  
Maximum Hardness Principle ◽  
Theoretical Results

The regioselectivity of hetero Diels–Alder reactions (HDA) of 2-azabutadiene with aldehydes has been elucidated by means of Gazquez–Mendez rules, which are based on the calculation of local softnesses of the four terminal atoms involved in cyclization. The theoretical results obtained with the B3LYP/6-31G(d) method confirm the regioselectivities observed experimentally for all substituents ( R = H , CH 3, CN ) present in the aldehyde reactant. The regioselectivities of these HDA reactions have been confirmed by the calculation of the activation barriers corresponding to the two cyclization modes, and also by the application of the Houk rule and the maximum hardness principle.

scholarly journals An Assessment of the Validity of the Maximum Hardness Principle in Chemical Reactions

2017 ◽  
Vol 56 (3) ◽  
Author(s):  
Jordi Poater ◽  
Marcel Swart ◽  
Miquel Solà
Keyword(s):  
Transition State ◽  
Chemical Reactions ◽  
Maximum Hardness ◽  
Maximum Hardness Principle

We have computationally explored the fulfillment of the Maximum Hardness Principle in chemical reactions. To this end we have selected a well-defined series of 34 exothermic chemical reactions (the so-called BH76 test) and we have calculated the hardness of reactants, transition state, and products. Our results show that for only 18% of the reactions studied the hardness of the reactants is, at the same time, lower than that of the products and greater than that of the transition state, in agreement with the Maximum Hardness Principle. In most reactions we find that either the transition state has a higher hardness than the reactants or the reactants are harder that the products or both, and, therefore our results show that the Maximum Hardness Principle is disobeyed in most chemical reactions.

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