The Interrelation of Reaction and Substituent Constants and the Role of Electronegativity in Linear Free Energy or Enthalpy Relationships

1961 ◽  
Vol 83 (16) ◽  
pp. 3498-3503 ◽  
Author(s):  
W. F. Sager ◽  
Calvin D. Ritchie
Keyword(s):  
Free Energy ◽  
Linear Free Energy ◽  
Substituent Constants

Linear free energy relationships. VIII. Ionization potentials of aliphatic compounds

1977 ◽  
Vol 55 (14) ◽  
pp. 2637-2641 ◽  
Author(s):  
Harry W. Gibson
Keyword(s):  
Free Energy ◽  
Solution Phase ◽  
Ionization Potentials ◽  
Linear Free Energy Relationships ◽  
Aliphatic Compounds ◽  
Linear Free Energy ◽  
Energy Relationships ◽  
Ring Nitrogen ◽  
Substituent Constants ◽  
A Site

Ionization potentials (IP) of HX, CH3X, C2H5X, and i-C3H7X, where X is a substituent with non-bonded electrons, are directly proportional to ionization potentials of 4-substituted quinuclidines. This is taken as evidence that in general the energy required to remove an electron from a substituent X, as is the case in HX, CH3X, C2H5X, and i-C3H7X, is directly proportional to the energy required to remove an electron from a site remote from the substituent, as in the quinuclidines in which an electron is lost from the ring nitrogen. Furthermore, the IP's of the HX-i-C3H7X series are directly proportional to inductive substituent constants, σI, providing a valuable correlation between gas and solution phase behavior.

Half-wave potentials of quinone methides in dimethylformamide: Substituent effects

1981 ◽  
Vol 46 (4) ◽  
pp. 861-872 ◽  
Author(s):  
Josef Krupička ◽  
Bohumír Koutek ◽  
Lubomír Musil ◽  
Libuše Pavlíčková ◽  
Milan Souček
Keyword(s):  
Free Energy ◽  
Substituent Effects ◽  
Linear Free Energy Relationship ◽  
Quinone Methides ◽  
Linear Free Energy ◽  
Diffusion Controlled ◽  
Half Wave ◽  
Substituent Constants ◽  
Series Type ◽  
Spin Densities

Half-wave potentials of two series of quinone methides A have been determined in 0.1M tetrabutylammonium perchlorate in dimethylformamide. the first series (type I; 14 compounds) contained fuchsones substituted in positions 2 and 2,6 of the quinonoid ring, the second series (type II and III; 17 compounds) consisted of 2,6-ditert-butylquinone methides, with substituents at the exocyclic C(7) carbon atom. Properties of the first polarographic wave proved that in both series the reaction is one-electron, reversible, diffusion-controlled process. Linear free energy relationship was found between E1/2 and dual substituent constants σI and σR. Statistical analysis of linear free energy relationship for 2- and 2,6-substituted derivatives proved absence of steric factor in transmission of electronic substituent effect. The experimental results were interpreted on the basis of LUMO energies and spin densities, calculated by the HMO method.

Experimental and theoretical investigation of the unusual substituent effect of the vinyl group

1980 ◽  
Vol 58 (4) ◽  
pp. 412-417 ◽  
Author(s):  
W. F. Reynolds ◽  
T. A. Modro ◽  
P. G. Mezey ◽  
E. Skorupowa ◽  
A. Maron
Keyword(s):  
Free Energy ◽  
Substituent Effect ◽  
Phenyl Ring ◽  
Linear Free Energy Relationship ◽  
Ion Transfer ◽  
Hydride Ion ◽  
Linear Free Energy ◽  
Substituent Constants ◽  
Vinyl Group ◽  
Hydride Ion Transfer

σ+ Substituent constants for the ortho- and para-vinyl group have been determined by the application of the linear free-energy relationship to the nitration of the β-substituted styrene derivatives.Energy changes (relative to benzene system) for the proton and hydride ion transfer to individual positions in the styrene molecule have been calculated. Both approaches indicate that the vinyl group is capable of stabilizing both positively and negatively charged transition states. The interactions of the vinyl group with other substituents in the phenyl ring are also determined. Again, stabilizing effects with respect to both π-donor and π-acceptor substituents have been demonstrated for the vinyl group.

Theoretical investigation of experimentally determined α-εffects — The role of electronics

2011 ◽  
Vol 89 (11) ◽  
pp. 1343-1354 ◽  
Author(s):  
D. Afzal ◽  
K.R. Fountain
Keyword(s):  
Free Energy ◽  
Energy Surface ◽  
Methyl Formate ◽  
Electronic Effects ◽  
Linear Free Energy ◽  
High Level ◽  
Sn2 Pathway ◽  
Fluorinated Alkoxides

Recent experimental reports involving both α-nucleophiles and normal nucleophiles have reported both the presence and absence of an α-effect. In ester systems, such as dimethylmethylphosphonate (DMMP), a small α-effect is reported, but the reference point is a stationary point of the potential energy surface that must rearrange to acquire the near attack conformation (NAC) necessary for the Sn2 pathway to proceed. The second type of study involves use of highly fluorinated alkoxides as normal nucleophiles and reports no α-effect. This paper employs linear free energy plots in an investigation of electronic effects in methyl formate SN2 reactions, using high-level computations of transition states for determination of energy barriers.

Hydrogen Atom Transfer Reaction Free Energy as a Predictor of Abiotic Nitroaromatic Reduction Rate Constants: A Comprehensive Analysis

2019 ◽  
Author(s):  
Dominic Di Toro ◽  
Kevin P. Hickey ◽  
Herbert E. Allen ◽  
Richard F. Carbonaro ◽  
Pei C. Chiu
Keyword(s):  
Free Energy ◽  
Hydrogen Atom ◽  
Hydrogen Atom Transfer ◽  
Energy Model ◽  
Second Order ◽  
Transfer Model ◽  
Atom Transfer ◽  
Order Rate ◽  
Linear Free Energy ◽  
Free Energy Model

<div>A linear free energy model is presented that predicts the second order rate constant for the abiotic reduction of nitroaromatic compounds (NACs). For this situation previously presented models use the one electron reduction potential of the NAC reaction. If such value is not available, it has been has been proposed that it could be computed directly or estimated from the electron affinity (EA). The model proposed herein uses the Gibbs free energy of the hydrogen atom transfer (HAT) as the parameter in the linear free energy model. Both models employ quantum chemical computations for the required thermodynamic parameters. The available and proposed models are compared using second order rate constants obtained from five investigations reported in the literature in which a variety of NACs were exposed to a variety of reductants. A comprehensive analysis utilizing all the NACs and reductants demonstrate that the computed hydrogen atom transfer model and the experimental one electron reduction potential model have similar root mean square errors and residual error probability distributions. In contrast, the model using the computed electron affinity has a more variable residual error distribution with a significant number of outliers. The results suggest that a linear free energy model utilizing computed hydrogen transfer reaction free energy produces a more reliable prediction of the NAC abiotic reduction second order rate constant than previously available methods. The advantages of the proposed hydrogen atom transfer model and its mechanistic implications are discussed as well.</div>

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.

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