Steric manipulation of the lone pair in piperidine

✍ Scribed by Joseph B. Lambert; David S. Bailey; Barbara F. Michel

• Publisher: Elsevier Science
• Year: 1970
• Tongue: French
• Weight: 229 KB
• Volume: 11
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)97804-9

✦ Synopsis

The remarkable preference of single-atom substituents for the axial position in certain molecules of the structure 11s2 was first satisfactorily explained by Allinger, et al.3 Their --Ia Ie Ha IIe analysis showed that the interactions in Ia between the axial proton on X and the 3,5-axial protons are attractive, and that Ia possesses two fewer gauche H-H interactions than Ie. Such an explanation obviates the unpleasant necessity of attributing the equatorial lone -pair preference to steric bulk. Although several examples of such a preference have now been recorded?*2 the causative factors have not been the subject of direct, experimental tests. This paper describes experiments that offer conclusive evidence that the axial-proton-equatorial-lonepair situation is favored by net attractive N-proton interactions rather than by repulsive lonepair interactions.