1H NMR study of lithium d-lactate

✍ Scribed by M.L. Buszko; E.R. Andrew

• Book ID: 103963663
• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 483 KB
• Volume: 1
• Category: Article
• ISSN: 0926-2040
• DOI: 10.1016/0926-2040(92)90011-w

✦ Synopsis

Polycrystalline D-lactic acid lithium salt [(R)-2-hydroxypropanoic acid lithium salt, lithium D-lactate] has been investigated by pulsed proton magnetic resonance methods between 77 and 300 K at 25 MHz. The main relaxation mechanism is methyl rotation; the motion is characterized by an activation energy Ea = 14.5 +/- 0.5 kJ/mol and time factor tau 0 = (1.5 +/- 0.5) x 10(-13) s. The activation energy is higher than the potential barrier obtained by ESR and ENDOR techniques for methyl rotation in the lactate radical. The methyl rotation is also responsible for a reduction of the dipolar second moment. Below 100 K the reduction of the dipolar second moment is ascribed to quantum-mechanical tunneling; an excitation energy of 6.1 +/- 1 kJ/mol is derived from a contribution to the spin-lattice relaxation times from the tunneling.