Comparative Study of Topological and Linear Free Energy-Related Parameters for the Prediction of GC Retention Indices

<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>

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Linear Free Energy Relationship Analysis of Solvent Effects on Singlet Oxygen Reactions

Current Organic Chemistry ◽

10.2174/1385272033486657 ◽

2003 ◽

Vol 7 (9) ◽

pp. 799-819 ◽

Cited By ~ 15

Author(s):

Else Lemp ◽

Antonio Zanocco ◽

Eduardo Lissi

Keyword(s):

Free Energy ◽

Singlet Oxygen ◽

Solvent Effects ◽

Linear Free Energy Relationship ◽

Relationship Analysis ◽

Linear Free Energy

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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

Canadian Journal of Chemistry ◽

10.1139/v04-081 ◽

2004 ◽

Vol 82 (8) ◽

pp. 1294-1303 ◽

Cited By ~ 19

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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Congener-specific partition properties of chlorinated paraffins evaluated with COSMOtherm and gas chromatographic retention indices

Scientific Reports ◽

10.1038/s41598-021-84040-z ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Jort Hammer ◽

Hidenori Matsukami ◽

Satoshi Endo

Keyword(s):

Chemical Properties ◽

High Volume ◽

Retention Indices ◽

Chromatographic Retention ◽

Linear Free Energy Relationship ◽

Linear Free Energy ◽

Chlorinated Paraffins ◽

Gas Chromatographic Retention Indices ◽

High Volume Production ◽

Volume Production

AbstractChlorinated Paraffins (CPs) are high volume production chemicals and have been found in various organisms including humans and in environmental samples from remote regions. It is thus of great importance to understand the physical–chemical properties of CPs. In this study, gas chromatographic (GC) retention indexes (RIs) of 25 CP congeners were measured on various polar and nonpolar columns to investigate the relationships between the molecular structure and the partition properties. Retention measurements show that analytical standards of individual CPs often contain several stereoisomers. RI values show that chlorination pattern have a large influence on the polarity of CPs. Single Cl substitutions (–CHCl–, –CH2Cl) generally increase polarity of CPs. However, many consecutive –CHCl– units (e.g., 1,2,3,4,5,6-C11Cl6) increase polarity less than expected from the total number of –CHCl– units. Polyparameter linear free energy relationship descriptors show that polarity difference between CP congeners can be explained by the H-bond donating properties of CPs. RI values of CP congeners were predicted using the quantum chemically based prediction tool COSMOthermX. Predicted RI values correlate well with the experimental data (R2, 0.975–0.995), indicating that COSMOthermX can be used to accurately predict the retention of CP congeners on GC columns.

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Absorption Spectra of Substituted 2-Phenylindan-1,3-Dion-2-YL Radicals in Solution

Zeitschrift für Naturforschung A ◽

10.1515/zna-1983-1209 ◽

1983 ◽

Vol 38 (12) ◽

pp. 1337-1341

Author(s):

J. Zechner ◽

N. Getoff ◽

I. Timtcheva ◽

F. Fratev ◽

St. Minchef

Keyword(s):

Free Energy ◽

Absorption Spectra ◽

Flash Photolysis ◽

Bathochromic Shift ◽

Substitution Effects ◽

Linear Free Energy Relationship ◽

Linear Free Energy

Abstract Flash photolysis of a series of 2-phenylindandione-1,3 derivatives substituted in the 4′ position results in both the formation of stable benzylidenephthalides and of phenylindan-1,3-dion-2-yl radicals. The u. v. absorption maxima of these radicals are dependent on the solvent and show a bathochromic shift upon substitution. These substitution effects were correlated by means of a linear free energy relationship. Attempts were made to draw conclusions concerning the changes in the gap of the states involved and their curvature due to substitution.

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