PHYSICAL PROPERTIES
 

APPLICATION FIELDS

¹¹B NMR spectroscopy has been largely used in the boron chemistry (borane, borates, carboranes, polyhedral boranes ...) ( 93ACSR109 )

A typical reference sample is BF₃.OEt₂ in CDCl3 (absolute frequency of 32.083974 MHz with respect to 100.00 MHz for 11B). Also see IUPAC recommendations for reporting the NMR chemical shits of all nuclei relative to the ¹H resonance of TMS (02JMR323-156).

Some interesting features of B nuclei are:

¹¹B NMR is preferred over ¹⁰B NMR.

¹¹B chemical shift range between +100 and -120 ppm.

ⁿJ(¹¹B,X)=3*ⁿJ(¹⁰B,X)

Both ¹¹B and ¹⁰B are quadrupolar nuclei and the quadrupolar relaxation mechanism is often the dominant one of these nuclei. Thus, the boron NMR signal is usually broad (>10Hz).

Short T₁ values (10^-2-10^-3 s for ¹¹B) except in symmetrical environments.

¹J(¹¹B-¹¹B)=10-60Hz and ¹J(¹¹B-¹H)=40-160Hz in polyhedral boranes.

In boron-containing compounds the following experiments can be helpful:

• ¹¹B-decoupled vs ¹¹B-coupled ¹H experiment.
• ¹H-decoupled vs ¹H-coupled ¹¹B experiment.
• Conventional ¹H-decoupled ¹³C spectrum from which ¹J(¹⁰B,¹³C) and ^1,nJ(¹¹B,¹³C) coupling constants can be measured.
• 2D ¹¹B-¹H heteronuclear correlations (HETCOR) experiments ( 84JCR198 ).
• 2D ¹¹B-¹¹B COSY ( 82JACS4716 , 84JACS29 and 88AR205 ) and TOCSY ( 95POL961 ) experiments.
• 2D ¹³C-¹¹B HETCOR experiment ( 94MRC436 ).

An excellent review on Boron NMR can be found in 96ENC1002 . More information in 00ENC691 .

88AR61 , 88AR204