Zusammenfassung
Hindered rotation about the C(sp2) − C(sp3) bond in 2-isopropylmesitylene (3), 1-isopropyl-2-methylnaphthalene (4), and 9-isopropylanthracene (5) is investigated by 13C NMR spectroscopy. At low temperatures, 4 exists as two rotamers 4a and 4b of different populations. Since their conformations are known from 1H NMR spectra, assignment of the 13C signals to 4a and 4b is possible. The knowledge ...
Zusammenfassung
Hindered rotation about the C(sp2) − C(sp3) bond in 2-isopropylmesitylene (3), 1-isopropyl-2-methylnaphthalene (4), and 9-isopropylanthracene (5) is investigated by 13C NMR spectroscopy. At low temperatures, 4 exists as two rotamers 4a and 4b of different populations. Since their conformations are known from 1H NMR spectra, assignment of the 13C signals to 4a and 4b is possible. The knowledge thus obtained, of the influence of the blocked isopropyl group on the δ-values of other carbon atoms, allows signal assignments to be made in the low temperature spectra of 3 and 5. The unusual long-range effect of the isopropyl group on 13C chemical shifts is explained by non-bonded interactions.
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