Gauche Effect (gauche + effect)

Distribution by Scientific Domains


Selected Abstracts


ChemInform Abstract: The Fluorine,Iminium Ion Gauche Effect: Proof of Principle and Application to Asymmetric Organocatalysis.

CHEMINFORM, Issue 34 2009
Christof Sparr
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


Probing the influence of stereoelectronic effects on lithium affinity in 1,3- and 1,4-dioxa systems

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2001
Bishwajit Ganguly
Abstract A combined computational and structural study of the lithium affinity (LA) of O,C,O systems exhibiting the anomeric effect and of O, C,C,O systems exhibiting the gauche effect is presented. QM ab initio calculations using the MP2/6,31G* basis set were carried out on the gas-phase lithium affinities of dimethoxymethane (DMOM), dimethoxyethane (DMOE), 1,3-dioxane (DOX) and cis - and trans -tetraoxadecalin (TOD), along with that of dimethyl ether and of its dimer as reference compounds. Structural parameters were retrieved from the Cambridge Structural Database (CSD) for diethyl ether dimer and O,C,C,O lithium complexes and these agreed well with the calculated data. The computed lithium affinities of dimethoxymethane and dimethoxyethane were found to be conformationally dependent. The LAs are conformationally dependent (wherever applicable) and decrease in the order: (Me2O)2 >,DMOE >,DMOM >,DOD >,DOX >,trans -TOD, but cis -TOD restores the high LA (better than DMOE) by virtue of multiple coordination. Copyright © 2001 John Wiley & Sons, Ltd. [source]


Synthesis and structure elucidation of bromination products from dibromohomobenzonorbornadienes: high temperature bromination,Part 17,

MAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2005
Cavit Kazaz
Abstract The electrophilic addition of bromine to dibromohomobenzonorbornadiene derivatives at ,45 ± 5°C led to the formation of the rearranged and non-rearranged tetrabromides in a ratio of 6:4. However, high-temperature bromination of the same system in CCl4 at 77°C produced only non-rearranged products. The formation mechanism of the isomers and the role of the substituent on the rearrangement is discussed. The structure elucidation of the isomeric tetrabromides was achieved from NMR spectral data. The agreement between the calculated dihedral angles and the measured coupling constants is especially excellent. The ,-gauche effect is discussed. Copyright © 2004 John Wiley & Sons, Ltd. [source]


Leucine Side-Chain Conformation and Dynamics in Proteins from 13C NMR Chemical Shifts

CHEMBIOCHEM, Issue 9 2009
Frans A. A. Mulder Dr.
Abstract Look to the left: The carbon nucleus of a substituent in the gauche position about a subtending dihedral angle experiences an NMR chemical shift of about 5 ppm relative to the same chemical group present in the trans position. We demonstrate that this ",-gauche effect" can be utilized to determine the conformation and extent of rotameric averaging for leucine amino acid side chains in the protein calbindin D9k. The success of this approach suggests that rules can be established to define the orientation of other side chains in proteins as well, offering an easy gauge of protein side-chain flexibility, as well as avenues to advance protein structure determination by using side-chain chemical shifts. [source]


NMR, solvation and theoretical investigations of conformational isomerism in 2-X-cyclohexanones (X=NMe2, OMe, SMe and SeMe)

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2003
Matheus P. Freitas
Abstract The conformational equilibria of 2- N,N -dimethylamino- (1), 2-methoxy- (2), 2-methylthio- (3) and 2-methylselenocyclohexanone (4) were determined in various solvents by measurement of the 3JH-2,H-3 couplings. The observed couplings were analyzed using theoretical and solvation calculations to give both the conformer energies in the solvents studied plus the vapor-phase energies and the coupling constants for the distinct conformers. These gave the conformer energies and couplings of 2,4. The intrinsic couplings for the 2- N,N -dimethylamino compound were determined by the molecular mechanics PCMODEL program. The axial conformation in 1 is the most polar and also more stable in DMSO solution (Eeq,Eax=0.05,kcal,mol,1) and the pure liquid, while the equatorial conformer predominates in the remaining solvents studied (except in CCl4, where self-association is observed). In the methoxy ketone (2) the equatorial conformation is more stable in the vapor (Eeq,Eax=,0.30,kcal,mol,1) and in all solvents. The opposite behavior is shown by 3 and 4, where the axial conformation is the more stable one in the vapor phase (Eeq,Eax=1.60 and 2.95,kcal,mol,1 for 3 and 4, respectively) and is still the prevailing conformer in solution. The axial predominance for 3 and 4 is attributed to hyperconjugation between the electron lone pair of the hetero-substituent and the ,*CO orbital. This interaction is stronger for 3 and 4 than in the case of 1 and 2, where the ,gauche effect' in the equatorial conformation should be more effective in stabilizing this conformation. Copyright © 2003 John Wiley & Sons, Ltd. [source]