A General Treatment of Electrical Effects

Charton, Marvin

doi:10.1002/9780470171950.ch6

Cited by 112 publications

(6 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The values of σ I,n were given 46 by eq 3 where σ I (R i ) is the individual Hammett constant , σ I of each R group bonded to the tetrahedral carbon in the positions α to the nitroxyl function. All individual σ I constants were not known, and the missing ones were estimated with eqs 4 and 5.…”

Section: Resultsmentioning

confidence: 99%

“…b Individual steric constants r (R i ) are given in ref unless otherwise mentioned. c Individual polar constant σ I (R i ) are given in refs and unless otherwise noted. d In text, r (C5) is used for CR 2 (CH 2 ) 2 CR 2 ; r (C5 ‘ ) for (CH 2 ) 4 ; r (C5‘ ‘) for CR 2 NMeC(O)CR 2 ; r (C6) for CR 2 (CH 2 ) 3 CR 2 , CR 2 CH 2 C(O)CH 2 CR 2 , and CR 2 CH 2 CHOHCH 2 CR 2 ; r (C6 ‘ ) for CR 2 CH 2 NRC(O)CR 2 , CR 2 CH 2 C(O)CMeHCR 2 CR 2 CH 2 CHOAcCMeHCR 2 , and CR 2 CH 2 CHOHCMeHCR 2 ; r (C6 ‘ ‘ ) for (CH 2 ) 5 ; r (C7) for CR 2 (CH 2 ) 2 CHOHCH 2 CR 2 ; r (C7 ‘ ) for CR 2 (CH 2 ) 2 C(O)CH 2 CR 2 and CR 2 CH 2 NHC(O)CH 2 CR 2 ; r (C7 ‘ ‘ ) for (CH 2 ) 6 ; r (C7‘ ‘‘) for CR 2 CMeHNHC(O)CH 2 CR 2 ; r (C8) for CR 2 (CH 2 ) 2 CHOH(CH 2 ) 2 CR 2 and CR 2 (CH 2 ) 3 CHOHCH 2 CR 2 ; and r (C8 ‘ ) for CR 2 (CH 2 ) 2 C(O)(CH 2 ) 2 CR 2 and CR 2 (CH 2 ) 3 C(O)CH 2 CR 2 .…”

Section: Resultsmentioning

confidence: 99%

“…For alkoxyamines 16 and 40 , it was assumed that the polar effects of the CH 2 OMe and CH 2 OCH 2 Ph groups were very close, i.e. σ I (CH 2 OCH 2 Ph) ≈ σ I (CH 2 OMe), − as well their steric demands, i.e., r (CH 2 OCH 2 Ph) ≈ r (CH 2 OMe), by virtue of the minimum steric interaction (MSI) principle. , Since the O−Si bond is longer than the O−C bond, the steric demand of the OSiMe 2 t -Bu group was expected to be smaller than that of the methoxy group; that is, r (CH 2 OSiMe 2 t -Bu) = −0.30 was the best fitting value of eq 1. For alkoxyamines carrying groups capable of intramolecular hydrogen bonding (IHB) in positions 2 and 6 on the ring of the nitroxyl fragment (stars in Figure ), the E s,n values were estimated with r (C6) and r (CH 2 OH) for 19 , 22 , 29 , and 31 .…”

Section: Resultsmentioning

confidence: 99%

See 2 more Smart Citations

Steric and Polar Effects of the Cyclic Nitroxyl Fragment on the C−ON Bond Homolysis Rate Constant

et al. 2005

View full text Add to dashboard Cite

Alkoxyamines and persistent nitroxyl radicals are important regulators of nitroxide mediated radical polymerization (NMP). Because polymerization times decrease with increasing rate constant of the homolysis of the C-ON bond between the polymer chain and the nitroxyl moiety, the factors influencing the cleavage rate constant are of considerable interest. Here, we present the measurements of the rate constants (k d) of the C-ON bond cleavage in new cyclic alkoxyamine models. The homolysis rate constants of 9 new alkoxyamines and 33 others given by the literature are analyzed with regards to the contributions of the polar inductive/field (σ I) effect, the steric (Es) effect and the intramolecular hydrogen bonding (IHB) effect of the nitroxyl moieties, using the multiparameter equation established by Marque, i.e., log(k d/kd,0) ) -3.07σI -0.88Es -5.88. Cyclic steric constants r(Ri) for seven-and eightmembered rings are developed. Analysis of the results provides new insight on the importance of the conformation of the alkoxyamine on the values of k d.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Steric and Polar Effects of the Cyclic Nitroxyl Fragment on the C−ON Bond Homolysis Rate Constant

et al. 2005

View full text Add to dashboard Cite

show abstract

“…Importantly, stabilization and polarity effects are aliased and, then, the various effects are accounted for by eq in which the electrical Hammett constant σ L describes the stabilization/polar effect of EWG, and E s describes the steric effect of the substituents Thus, it was possible to estimate σ L of 0.1, 0.28, 0.4, 0.4, 0.59, 0.59, and 0.61 for 4 – , 6 , 7 , 2 – 5 , respectively. − From eq , increasing polarity of EWG leads to a decrease in k d due to the negative sign of the coefficient. Hence, k d is expected to decrease in the series 4 – > 6 > 2 ≈ 7 > 3 ≈ 4 > 5 as σ L increases.…”

Section: Discussionmentioning

confidence: 99%

C–ON Bond Homolysis of Alkoxyamines, Part 11: Activation of the Nitroxyl Fragment

et al. 2016

View full text Add to dashboard Cite

A few years ago, Bagryanskaya and colleagues (J. Org. Chem. 2011) showed that protonation of the nitroxyl fragment deactivated the alkoxyamine C-ON bond. Conversely, our group showed that protonation (Chem. Commun. 2011), as well as other chemical reactions such as oxidation or amine quaternization (Org. Lett. 2012), of the pyridyl moiety carried by the alkyl fragment was suitable to activate the homolysis of the C-ON bond. To pursue our goal of applying alkoxyamines as theranostic agents (Org. Biomol. Chem. 2014 and Mol. Pharmaceutics 2014) by activation of the C-ON bond homolysis, we turned our interest to the chemical activation of the nitroxyl fragment by oxidation/reduction of selected functions. Conversion of a hydroxyl group located close to the nitroxyl moiety successively into aldehyde, then acid, and eventually into ester, led to a successive decrease in kd.

show abstract

“…We also reported that the long-range polar effect of the alkyl ester group causes an increase in the k d values, but to different extents depending on the diastereoisomer. [29,31] However, for 1 b-f, one would expect a clear decrease in k d because of the electrondonating properties of the carboxylate group as shown by the lower Hammett constant for the carboxylate group [36] (s COO À = À0.19) than for the acid group [36] (s COOH = 0.30). However, the absence of significant changes in k d for the RR/SS isomers makes this possibility unlikely.…”

Section: Wwwchemphyschemorgmentioning

confidence: 93%

Effect of the Carboxylate Salt on the CON Bond Homolysis of SG1‐Based Alkoxyamines

et al. 2008

View full text Add to dashboard Cite

Alkoxyamines and persistent nitroxides are important regulators of the nitroxide mediated radical polymerization (NMP). Since the polymerization time decreases with increasing values of the homolysis rate constant (kd) for the C--ON bond between the polymer chain and the nitroxide moiety, the factors influencing kd are of considerable interest. Environmentally friendly polymerization methods, such as NMP in emulsion medium, have now been developed. The success of the polymerization depends not only on the strength of the C--ON bond but also on the solubility of the initiator/controller alkoxyamines, which control the nucleation. Various salts of SG1-based alkoxyamines (S+-OOCCMeH-SG1) labelled 1 a-f, where S+=Li+ (a), Na+ (b), K+ (c), nBu3HN+ (d), NH4+ (e), and nBu4N+ (f) are prepared, all of which are soluble in most organic solvents (e.g. pentane, dichlomethane, benzene, ethanol, etc.) as well as in water. Their kd values, which are measured in tert-butylbenzene, reveal unexpected behaviors depending on the diastereoisomers. For the RR/SS diatereoisomers (i.e. slowly homolyzing isomers), kd was not found to be sensitive to any of the salts, whereas for the RS/SR diastereoisomers (i.e. quickly homolyzing isomers), kd is observed to decrease to a greater or lesser extent depending on the type of salt. The conformations of the diastereoisomers of several salts are determined by means of DFT calculations, and the orbital interactions are studied by natural bond orbital (NBO) analysis.

show abstract

A General Treatment of Electrical Effects

Cited by 112 publications

References 15 publications

Steric and Polar Effects of the Cyclic Nitroxyl Fragment on the C−ON Bond Homolysis Rate Constant

Steric and Polar Effects of the Cyclic Nitroxyl Fragment on the C−ON Bond Homolysis Rate Constant

C–ON Bond Homolysis of Alkoxyamines, Part 11: Activation of the Nitroxyl Fragment

Effect of the Carboxylate Salt on the CON Bond Homolysis of SG1‐Based Alkoxyamines

Contact Info

Product

Resources

About