Heterocycles conformation

Q Which of the following heterocycles conform to the Huckel rule (4h +2) for aromaticity (i) furan (ii) l//-azepine (iii) pyrylium perchlorate [chlorate(VIl)] ... 

As mentioned in connection with the benzoyl derivatives of five-membered heterocycles, conformational analysis of benzoyl derivatives of pyridine suffers from the indetermination connected with the necessity of simultaneously assigning N,0-cis/trans populations and conformer structures from experimental results. The all-planar conformations should be excluded... 

Emphasis is placed on simply substituted free bases. The problems of conformational equilibria in /V-alkylpiperidinium salts and N-quaternization reactions and the relationships of these to conformational equilibria in the free bases are not covered, since this area is a large one requiring separate treatment. In other relevant previous reviews, the topics include heterocyclic conformational analysis,3-7 interactions in azacyclic systems,8 the conformational analysis of piperidine,9 hexahydropyrimidines,10,11 hexahydropyri-dazines,12 quinolizidines,13 the conformational analysis of bi- and polycyclic... 

Eliel has been involved for many years in heterocyclic conformational analysis, and has made important contributions to investigations related to the anomeric effect. In this volume, Eliel and Juaristi present important data for systems of the type X-C-C-Y (X, Y = heteroatoms), and discuss repulsive gauche effects. Attractive gauche effects have long been known, and a theoretical connection of the gauche effect with the anomeric effect has been made. However, the repulsive interactions were not well recognized until recently. 

Saturated six-membered N-heterocycles, conformational analysis of 8IAG567. 

In the former the heterocyclic conformation is closer to a halfchair with a Cg axis passing through C-4 than an envelope with S at the flap. The OH of the COOH is H-bonded to the sulfoxide 0. A highly specific gas chromatographic method has been... 

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