1H and 13C NMR chemical shifts in areneboronic acids
271
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0.05
0.04
0.03
0.02
0.01
0.00
138.8 138.7 138.6 138.5 138.4 138.3 138.2 138.1 138.0 137.9 137.8
140
135
130
125
Figure 1. 13C NMR spectrum of triphenylboroxane (7) in DMSO.
3
(t, J D 7.7 Hz, 1H, H-4). 13C NMR: υ D 22.57 (CH3ꢁ, 126.79
(5 mmol) with n-butyllithium (5.5 mmol) and subsequently
with tri-n-butyl borate (10 mmol).4,10 The melting-points
of boronic acids are questionable since dehydration with
the formation of the boroxanes readily occur at elevated
temperatures.9 For the sake of completeness, the high-
resolution NMR data for 1–6 are given, although 1, 2 and 5
are known compounds.
(C-3, C-5), 129.30 (C-4), 139.91 (C-2, C-6).
3,5-Di-tert-butylbenzeneboronic acid (6)
1
°
Yield 34%, m.p. 182 C. H NMR: υ D 1.42 [s, 18H, C(CH3ꢁ3],
7.69 (t, 4J D 2.0 Hz, 1H, H-4), 8.13 (d, 4J D 2.0 Hz, H-2, H-6).
13C NMR: υ D 31.83 [C(CH3ꢁ3], 35.22 [C(CH3ꢁ3], 127.74 (C-2,
C-6), 129.85 (C-4), 150.56 (C-3, C-5).
Benzeneboronic acid (1)
11
Yield 35%, m.p. 219 C (lit. m.p. 217–220 C). 1H NMR:
υ D 7.52 (dd, 3J D 7.2, 7.6 Hz, 2H, H-3, H-5), 7.61 (tt,
3J D 7.2 Hz, 4J D 1.5 Hz, 1H, H-4), 8.25 (dd, 3J D 7.6 Hz,
4J D 1.5 Hz, 2H, H-2, H-6). 13C NMR: υ D 128.41 (C-3, C-5),
133.13 (C-4), 136.07 (C-2, C-6).
°
°
NMR spectra
The NMR spectra of saturated (ca 10ꢀ2M) CDCl3 solutions
of 1–6 were measured at 300 K on a Bruker AMX 400
spectrometer (1H 400.13 MHz: 13C, 100.62 MHz). 1H NMR
spectra were recorded with a sweep width of 20 ppm with
64K data points and a digital resolution of 0.25 Hz per
point. 13C NMR spectra were recorded with a sweep width
of 331 ppm with 64K data points and a digital resolution
of 0.51 Hz per point after zero filling with 64 K. The 13C
NMR spectrum of 7 (Fig. 1) was observed when a solution of
100 mg of 1 in 2 ml of dry DMSO-d6 was measured at 300 K on
a Bruker GMX 500 spectrometer (125.77 MHz, 5000 scans).
The assignments are based on 1H–13C-COSY experiments
(1H) and the DEPT method (13C).
2-Methylbenzeneboronic acid (2)
12
1
°
°
Yield 30%, m.p. 158 C (lit. m.p. 171 C). H NMR: υ D 2.81
(s, 3H, CH3ꢁ, 7.25–7.34 (m, 2H, H-3, H-5), 7.45 (ddd,
3J D 7.5, 7.5 Hz, 4J D 1.4 Hz, 1H, 4-H), 8.22 (dd, 3J D 7.5 Hz,
4J D 1.4 Hz, 1H, H-6). 13C NMR: υ D 23.5 (CH3ꢁ, 125.60 (C-5),
131.00 (C-3), 132.62 (C-4), 137.65 (C-6), 146.69 (C-2).
3-tert-Butylbenzeneboronic acid (3)
1
°
Yield 37%, m.p. 221 C. H NMR: υ D 1.43 [s, 9H, C(CH3ꢁ3],
3
3
7.47 (dd, J D 7.6, 7.4 Hz, 1H, H-5), 7.65 (ddd, J D 7.6 Hz,
Acknowledgements
We thank the Fonds der Chemischen Industrie for financial support.
4J D 1.2, 1.1 Hz, 1H, H-4), 8.06 (ddd, J D 7.4 Hz, J D 1.2,
1.1 Hz, 1H, H-6), 8.31 (dd, 4J D 1.2, 1.2 Hz, 1H, H-2). 13C
NMR: υ D 31.77 [C(CH3ꢁ3], 35.1 [C(CH3ꢁ3], 128.25 (C-5),
130.24 (C-4), 132.70 (C-2), 133.17 (C-6), 150.88 (C-3).
3
4
REFERENCES
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4. Bruns S. Dissertation Thesis, University of Hamburg, 2002.
5. (a) Wrackmeyer B. Prog. Nucl. Magn. Reson. Spectrosc. 1979; 12:
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Mu¨ller K-D, Layton WJ, Komorowsky L. Z. Anorg. Allg. Chem.
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4-tert-Butylbenzeneboronic acid (4)
1
°
Yield 40%, m.p. 160 C. H NMR: υ D 1.38 [s, 9H, C(CH3ꢁ3],
3
3
7.54 (d, J D 8.2 Hz, 2H, H-3, H-5), 8.18 (d, J D 8.2 Hz, 2H,
H-2, H-6). 13C NMR: υ D 31.20 [C(CH3ꢁ3], 35.07 [C(CH3ꢁ3],
124.95 (C-3, C-5), 135.58 (C-2, C-6), 155.97 (C-4).
2,6-Dimethylbenzeneboronic acid (5)
13
Yield 21%, m.p. 120 C (lit. m.p. 125–130 C). 1H NMR:
°
°
6. No¨th H, Wrackmeyer B. In NMR—Basic Principles and Progress,
Diehl P, Fluck E, Kosfeld R (eds), vol 14. Springer: Berlin, 1978.
υ D 2.38 (s, 6H, CH3ꢁ, 6.99 (d, 3J D 7.7 Hz, 2H, H-3, H-5), 7.16
Copyright 2003 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2003; 41: 269–272