Conformational equilibria in N-alkylpiperidinium salts

✍ Scribed by Ernest L. Eliel; Chen-Yu Yen; Gabriela Zúñiga Juaristi; William R. Kenan Jr.

• Publisher: Elsevier Science
• Year: 1977
• Tongue: French
• Weight: 257 KB
• Volume: 18
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)83117-8

✦ Synopsis

The conformational equilibrium in N-methylpiperidines (Scheme 1) has been the object of much recent interest.lq7 Work by Booth6 and by our own group5 indicated that the values for -AGO of FH3 R-f e RaNCH3 1 R = c&-3,5-di-Me Scheme 1 less than 0.8 kcal/mol given in the earlier literature8 (see also ref. 7) cannot be correct. Recent work involving freezing of the equilibrium shown in Scheme 1 (e.g. for N-cis-3,5-dimethyl-piperidine, 1) by irreversible quenching of dilute solutions or dilute vapors of the amine by concentrated acid and NMR measurements of the composition of the salts so formed 1,234 supports a -AGO-value as high as 3.0 kcal/mol. Although we have earlier espoused a somewhat lower value,5 recent results from our own laboratories' and elsewhere' suggest that the 3.0 kcal/mol value is probably correct. For summaries of the earlier literature, see refs. 1 and 5.