Journal ArticleDOI
Carbon-13 substituent chemical shifts in the side-chain carbons of aromatic systems: the importance of π-polarization in determining chemical shifts
John Bromilow,Robert T. C. Brownlee,David J. Craik,Peter R. Fiske,Jeffrey E. Rowe,Maruse Sadek +5 more
TLDR
In this article, the side-chains of meta-and para-substituted benzenes of the type XC6H4COZ have been measured and the reverse inductive contribution observed is explained in terms of a π-polarization mechanism.Abstract:
13 C Substituent chemical shifts of the carbonyl sites in the side-chains of meta- and para-substituted benzenes of the type XC6H4COZ have been measured. Analysis of this data using the dual substituent parameter method shows that inductive effects are predominant. The reverse inductive contribution observed is explained in terms of a π-polarization mechanism. Critical support for this mechanism is obtained from additional series where the carbonyl is complexed with Lewis acids. The concepts of ‘extened’ and ‘localized’π-polarization are discussed.read more
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Ionic Liquid-Promoted, Highly Regioselective Heck Arylation of Electron-Rich Olefins by Aryl Halides
Jun Mo,Lijin Xu,Jianliang Xiao +2 more
TL;DR: The chemistry provides a simple, effective method for preparing branched, arylated olefins and contributes to the extension of Heck reaction to a wider range of substrates.
Journal ArticleDOI
New Strategies for the Design of Folded Peptoids Revealed by a Survey of Noncovalent Interactions in Model Systems
TL;DR: A new, modular design strategy has guided the construction of peptoids containing 1-naphthylethyl side chains, which it is shown can be utilized to effectively eliminate trans-amide rotamers from the peptoid backbone, yielding the most conformationally homogeneous class of peptoid structures yet reported in terms of amide rotamerism.
Journal ArticleDOI
Dendritic structure having a potential gradient: new synthesis and properties of carbazole dendrimers.
Ken Albrecht,Kimihisa Yamamoto +1 more
TL;DR: Overall, these data show the pi-polarization substituent effect of the carbazole unit, and their summation determines the potential gradient in the repeating dendritic structure of the Carbazole dendrimer.
Journal ArticleDOI
Energetics of an n → π* Interaction that Impacts Protein Structure
TL;DR: The trans/cis ratio of the amide bond in N-formylproline phenylesters correlates with electron withdrawal by a para substituent, and an analogous interaction can stabilize the conformation of trans peptide bonds, alpha-helices, and polyproline type-II helices.
Journal ArticleDOI
Electron-withdrawing substituents decrease the electrophilicity of the carbonyl carbon. An investigation with the aid of (13)C NMR chemical shifts, nu(C[double bond]O) frequency values, charge densities, and isodesmic reactions to interpret substituent effects on reactivity.
TL;DR: A significant ground-state destabilization of carboxylic acid esters, and Carbonyl compounds in general, due to the decreased resonance stabilization, is proposed as a novel concept to explain both the increase in their reactivity and the changes in the chemical shifts and carbonyl frequencies induced by electron-withdrawing substituents.
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