In problems 4.28 to 4.51, refer to Table 4.3 for isotopic abundances where needed.

NaBH₄ contains the tetrahedral [BH4]^– ion. Although NaBH₄ hydrolyses slowly in water, it is possible to obtain a clean ¹H NMR spectrum of the compound in D₂O. Naturally occurring boron consists of two isotopes: ¹¹B, 80.1%, I = 3/2, and ¹⁰B, 19.9%, I = 3. Assuming that a sharp, well-resolved spectrum is obtained, sketch the expected 400 MHz ¹H NMR spectrum (including a scale) if the signal for the protons occurs at  δ –0.2 ppm, and the values of J_11B1H = 80.5 Hz and J_10B1H = 27.1 Hz. How would the spectrum differ if it were recorded at 100MHz?

Table 4.3

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Nucleus ΤΗ ²H Li 11B 13C 170 19 F 23 Na 2 Al 29 Si 31 p 7 Se 103 Rh 117. Sn 119 Sn 19 Xe 183 W 195 pt 199 Hg Natural abundance/% >99.9 0.015 92.41 80.1 1.07 0.04 100 100 100 4.69 100 7.63 100 7.68 8.59 26.40 14.31 33.78 16.87 miele v + mk nh -k -le -le-le - -ki -k -k -IN Frequency of observation / MHz (referred to ¹H at 100 MHz) 100 15.35 38.9 32.1 25.1 13.5 94.0 26.45 26.1 19.9 40.5 19.1 3.2 35.6 37.3 27.7 4.2 21.5 17.9 Chemical shift reference (8 0 ppm)* SiMe SiMe4 LICI (1 M in H₂O) F3B-OEt2 SiMe H₂O CFC13 NaCl (1 M in H₂O) [Al(OH₂)]³+ SiMc4 H3PO4 (85%, aq) SeMe₂ Rh (metal) SnMc4 SnMe4 XeOF4 Na₂WO4 (in D₂O) Na₂ [PtCl6] HgMe₂