Conformational Study of Acyclic Alcohols by NMR Spectroscopic Analysis, Molecular Force Field and Ab Initio Calculations

• Published in: Bulletin of the Chemical Society of Japan Vol. 59; no. 10; pp. 3125 - 3130
• Main Authors: Abe, Kazuhisa, Ito, Kohichi, Suezawa, Hiroko, Hirota, Minoru, Nishio, Motohiro
• Format: Journal Article
• Language: English
• Published: Tokyo The Chemical Society of Japan 01.10.1986; Chemical Society of Japan
• Subjects: Atomic and molecular physics; Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics); Exact sciences and technology; Molecular properties and interactions with photons; Physics; Properties of molecules and molecular ions; Ab initio method; Theoretical study; Alcohol; Experimental study; Gaussian orbital; Shift reagent; Saturated aliphatic compound; Force field method; Alkanol; Lanthanide Complexes; NMR spectrum; Conformational equilibrium; Organic compounds; Conformation
• ISSN: 0009-2673; 1348-0634
• DOI: 10.1246/bcsj.59.3125

Conformations of a series of acyclic alcohols (CH3CH(R)CH(OH)CH3, CH3CH(R)CH(OH)CH(R′)CH3, and CH3CH(R)CH(OH)But) were studied (1) by measuring vicinal H–H coupling constants (3JH–H), (2) by lanthanoid-induced shift (LIS) analysis, (3) by molecular mechanics calculations (MM2), and (4) by ab initio (STO-3G, 4-31G geometry optimization) calculations. In the case of conformationally flexible alcohol as exemplified by 2-butanol and 3-pentanol, population of conformers determined by the LIS method do not agree with those determined by the 3JH–H, MM2, and ab initio methods. The discrepancy comes from the fact that the LIS measurement gives the most stable conformation of the alcohol in the LSR-alcohol complex and not of the free alcohol. In some flexible molecules, the most stable conformer in the complex can be different from that of the free molecule. In general, the conformational equilibrium is shifted by coordination of the shift reagent to the conformer whose alkyl chain stretches opposite to the direction of the coordination site of the shift reagent.