PHYSICAL PROPERTIES
 

APPLICATION FIELDS

Both ⁶Li and ⁷Li NMR spectroscopy has been extensively applied on inorganic and organometallic lithium-containing compounds as well as on biochemical and physiological studies. The ⁶Li isotope has the smallest quadrupole moment for any nucleus and it can be considered as an spin-1/2 nucleus. Therefore, sharp linewidths are achieved with compared to the ⁷Li isotope. Thus, despite its lowest sensitivity ⁶Li can be preferred instead of  ⁷Li detection. Specific labeling with ⁶Li has also been reported.

Both lithium isotopes are usually referenced to external standard references 0.1M or 1M LiCl in D₂O, THF-d₈ or Methanol-d₄ (absolute frequency: 14.716086 MHz for ⁶Li and 38.863797 MHz for ⁷Li with respect to 100.00 MHz of TMS resonance). Also see IUPAC recommendations for reporting the NMR chemical shits of all nuclei relative to the ¹H resonance of TMS (02JMR323-156).

• The ^6,7Li chemical shifts range is 12 ppm (from -9 ppm to +3 ppm).
• A great variety of J(^6,7Li ,X) coupling constants can be measured and succesfully applied to structural studies.
• Long T₁ relaxation times (of the order of seconds or even tens of seconds) may cause difficulties for ⁶Li measurements.

• 1D ¹H-decoupled vs ¹H-coupled ⁶Li spectrum with NOE enhancement. Selective ¹H-decoupling can also be applied.
• 2D ⁶Li-¹H correlation experiments using HETCOR ( 93JACS10871 ) or HMQC ( 93CB2747 ).
• 2D ⁶Li-¹H HOESY experiment ( 87JACS970 , 88MRC827 , 98JACS8143 , and 02MRC361 ).
• 2D ⁶Li-⁶Li EXSY experiment ( 90JACS6190 ).
• 2D ⁶Li-⁶Li correlation experiment using COSY ( 88JACS6033 and 86TL2251 ) or INADEQUATE ( 91MRC1065 and 92HCA883 ) pulse sequences.
• 2D ⁶Li-¹³C correlation experiments ( 87JACS5532 , 88JACS978 ).
• 2D ⁶Li-¹³C HMQC-TOCSY experiments ( 96JACS5450 ).
• 2D ⁶Li-¹⁵N correlation experiments ( 92MRC855 , 94JACS11602 ).
• 2D ⁶Li-³¹P correlation experiments ( 93JACS3475 ).

Interesting reviews on Li NMR: B96GIE247, 92ACC89 , 96ENC2807 .
The alkali Metals NMR: B79HAR129, 00ENC1584 .