Introduction to NMR Spectroscopy for Physical and Analytical Chemistry: The Case of the BF4ˉ Anion

Abstract

Włodzimierz Makulski

Simple 1D NMR measurements of an inorganic compound (NaBF4 ) in a water solution were proposed as an undergraduate exercise in the chemistry course. 19F NMR chemical shifts were measured in dilute aqueous solutions of tetrafluoro borate salts. The 11B/10B secondary isotope effect on the 19F chemical shift was stated as 1 Δδ19F(11B,10B)=-0.053 ppm. The peak integrations indicated an abundance of 11B (80.18%) and 10B (19.82%) in the current natural boron-containing salt. Spin-spin coupling constants 1 J(19F,10B)= ~ 0.53 Hz and 1 J(19F,11B)= ~ 1.55 Hz were found using the convolution procedure. Several additional properties of water solutions were given: 19F nuclear relaxation times, hydrolysis of BF4 Ë? anions, spin-spin nuclear magnetic couplings, and nuclear magnetic moments of boron isotopes. 10/11B abundance measurements using mass spectrometry (MS) were also included and briefly described.

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