Treatment of Steric Effects

Gallo, R.

doi:10.1002/9780470171936.ch3

Cited by 61 publications

(7 citation statements)

References 180 publications

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“…Numerous other sets of steric parameters have been conceived to measure bulkiness. Besides Winsteins A values [8] there are, for example, Tafts E s , [9] Meyers V a , [10] Hirotas W s , [11] and Beckhaus' S f [12] factors. We do not intend to supplant them by our B values.…”

Section: Resultsmentioning

confidence: 99%

B Values as a Sensitive Measure of Steric Effects

Ruzziconi

Spizzichino

Lunazzi

et al. 2009

Chemistry A European J

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Someone who says "A" should be prepared to also say "B": In contrast to cyclohexane model-based A values, biphenyl model-derived B values are powerful tools to quantify steric repulsion in and conformational behavior of ortho-substituted aromatic compounds.Torsional barriers of 15 ortho-substituted biphenyls have been determined computationally using the B3LYP density functional and experimentally by variable-temperature ("dynamic") nuclear magnetic resonance. Taking advantage of the 3'-isopropyldimethylsilyl group as a novel and superior diastereotopicity probe and tracking coalescence temperatures down to -173 degrees C (100 K), activation energies of aryl-aryl rotation as small as 5 kcal mol(-1) can be assessed. The 2-X/2'-H repulsion increments thus derived are powerful parameters for rationalizing and predicting the conformational behavior of aromatic compounds carrying ortho substituents.

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Section: Resultsmentioning

confidence: 99%

B Values as a Sensitive Measure of Steric Effects

Ruzziconi

Spizzichino

Lunazzi

et al. 2009

Chemistry A European J

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“…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 . For alkoxyamines 7 , 10 , 11 , 23 − 25 ‘, 27 , 34 , 37 , 42 , and 43 based on a six-membered ring nitroxyl fragment without substituents in position 3 (filled hexagons in Figure ), the values of E s,n were estimated with r (C6).…”

Section: Resultsmentioning

confidence: 99%

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

et al. 2005

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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.

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“…In the past 60 years, numerous sets of steric parameters have been designed to measure bulkiness such as Winstein's A values,145 Taft's E s ,146 Meyer's V a ,147 Hirota's Ω s ,148,149 and Beckhaus’ S f factor 150. Recently, an approach based on data from conformational analysis has been presented ( B value) 151–156.…”

Section: Theoretical Conformational Analysismentioning

confidence: 99%

Recent trends in conformational analysis

Mazzanti

Casarini

2011

WIREs Comput Mol Sci

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An outlook of the various research fields of organic chemistry where conformational analysis plays a fundamental role is presented. The section Methodologies for Conformational Analysis is focused on the information that can be obtained by various spectroscopic techniques such as nuclear magnetic resonance and optical methods such as electronic circular dichroism and vibrational circular dichroism. A comprehensive screening of the more recent ab initio and density functional theory theoretical approaches to conformational analysis is presented in the section Theoretical Conformational Analysis. The section Application of Conformational Analysis to the Determination of the AC of Organic Molecules shows how the synergic use of experimental and theoretical methods can solve challenging conformational tasks arising from modern organic chemistry. © 2011 John Wiley & Sons, Ltd. This article is categorized under: Electronic Structure Theory > Density Functional Theory

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Treatment of Steric Effects

Cited by 61 publications

References 180 publications

B Values as a Sensitive Measure of Steric Effects

B Values as a Sensitive Measure of Steric Effects

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

Recent trends in conformational analysis

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