Free-energy relationships in coordination chemistry. II. Requirements for linear relationships

1970 ◽  
Vol 48 (16) ◽  
pp. 2565-2573 ◽  
Author(s):  
E. Nieboer ◽  
W. A. E. McBryde
Keyword(s):  
Free Energy ◽  
Strong Interactions ◽  
Thermodynamic Quantities ◽  
Reaction Site ◽  
Independent Variables ◽  
Linear Free Energy ◽  
Linear Relationships ◽  
In Series ◽  
Energy Relationships ◽  
Equilibrium Relationships

This paper discusses factors predisposing to linear free energy relationships among families of metal complexes. It is postulated that changes occurring at a reaction site in a test series of reactions and the corresponding changes in a reference series have their origins in the same independent variables. Linearity is seen to be favored when changes in the reaction site or in ligand substituents are small, and in the absence of strong interactions with the solvent. In addition to such considerations of a molecular sort, a number of relationships among the thermodynamic quantities ΔH0, ΔS0, and ΔG0 which have been identified as having a significant influence on rate and equilibrium relationships in series of organic reactions are discussed in terms of their effect on metal–ligand systems.

scholarly journals LINEAR FREE ENERGY RELATIONSHIPS CONCERNING REACTION RATES IN MODERATELY CONCENTRATED MINERAL ACIDS

1966 ◽  
Vol 44 (16) ◽  
pp. 1917-1931 ◽  
Author(s):  
J. F. Bunnett ◽  
Fredric P. Olsen
Keyword(s):  
Free Energy ◽  
Transition State ◽  
Reaction Rates ◽  
Mineral Acid ◽  
Linear Free Energy Relationships ◽  
Linear Free Energy ◽  
Linear Relationships ◽  
Mineral Acids ◽  
Energy Relationships ◽  
Better Than

Linear relationships exist between log kψ + H0 (for reactions of weakly basic substrates) or log kψ (for reactions of strongly basic substrates) and (H0 + log [H+]). These are linear free energy relationships. For weakly basic substrates, the correlations obtained are better than in plots of (log kψ, + H0) versus log [Formula: see text] or of log kψ versus −H0. The slopes in plots of log kψ or (log kψ + H0), as appropriate, against (H0 + log [H+]) are taken as parameter, [Formula: see text], which characterizes the response of the reaction rate to changing mineral acid concentration. Values of [Formula: see text] for reactions of strongly basic substrates reflect only relationships between protonated substrate and transition state, and may be related to reaction mechanism. [Formula: see text] values for reactions of weakly basic substrates reflect both equilibrium protonation of the substrate and transformation of protonated substrate to transition state, and are therefore less directly related to mechanism. However, the [Formula: see text] values for the two steps are additive and that for the latter step can be obtained by subtraction if the overall [Formula: see text] value and that for equilibrium protonation are known.

Synthesis and characterization of a series of 1-methyl-4-[2-aryl-1-diazenyl]piperazines and a series of ethyl 4-[2-aryl-1-diazenyl]-1-piperazinecarboxylates

2004 ◽  
Vol 82 (8) ◽  
pp. 1294-1303 ◽  
Author(s):  
Vanessa Renée Little ◽  
Keith Vaughan
Keyword(s):  
Free Energy ◽  
Chemical Shifts ◽  
Linear Free Energy Relationship ◽  
Piperazine Ring ◽  
Linear Free Energy ◽  
In Series ◽  
Methylene Groups ◽  
Diazonium Coupling ◽  
The Difference

1-Methylpiperazine was coupled with a series of diazonium salts to afford the 1-methyl-4-[2-aryl-1-diazenyl]piperazines (2), a new series of triazenes, which have been characterized by 1H and 13C NMR spectroscopy, IR spectroscopy, and elemental analysis. Assignment of the chemical shifts to specific protons and carbons in the piperazine ring was facilitated by comparison with the chemical shifts in the model compounds piperazine and 1-methylpiperazine and by a HETCOR experiment with the p-tolyl derivative (2i). A DEPT experiment with 1-methylpiperazine (6) was necessary to distinguish the methyl and methylene groups in 6, and a HETCOR spectrum of 6 enabled the correlation of proton and carbon chemical shifts. Line broadening of the signals from the ring methylene protons is attributed to restricted rotation around the N2-N3 bond of the triazene moiety in 2. The second series of triazenes, the ethyl 4-[2-phenyl-1-diazenyl]-1-piperazinecarboxylates (3), have been prepared by similar diazonium coupling to ethyl 1-piperazinecarboxylate and were similarly characterized. The chemical shifts of the piperazine ring protons are much closer together in series 3 than in series 2, resulting in distortion of the multiplets for these methylenes. It was noticed that the difference between these chemical shifts in 3 exhibited a linear free energy relationship with the Hammett substituent constants for the substituents in the aryl ring. Key words: triazene, piperazine, diazonium coupling, NMR, HETCOR, linear free energy relationship.

Linear free energy relationships in CN bond dissociations in molecular ions of 4-substitutedN-(2-furylmethyl)anilines in the gas phase

2007 ◽  
Vol 42 (11) ◽  
pp. 1496-1503 ◽  
Author(s):  
Eduardo A. Solano Espinoza ◽  
Elena Stashenko ◽  
Jairo Martínez ◽  
Uriel Mora ◽  
Vladimir Kouznetsov
Keyword(s):  
Free Energy ◽  
Gas Phase ◽  
Molecular Ions ◽  
Linear Free Energy Relationships ◽  
Linear Free Energy ◽  
Energy Relationships
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