Neutral hyperconjugation challenged: No support from one-bond CC coupling constants
✍ Scribed by Krystyna Kamieńska-Trela
- Book ID
- 102528853
- Publisher
- John Wiley and Sons
- Year
- 1995
- Tongue
- English
- Weight
- 196 KB
- Volume
- 33
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
A significant decrease in 'l(Clpso, CH,) coupling constants from a value typical of C(sp2)-C(sp3) bonds (43.5 Hz or smaller) to the unexpectedly low value of 36 Hz typical of C(sp3jC(sp3) bonds was reported by Lambert and Singer on passing from XC,H,CH,Sn(CH,), to XC,H,CH,C(CH,), (X = H, CH, , OCH, , NO,). This trend was invoked by these authors as the first evidence for neutral hyperconjugation in terms of coupling constants. However, the present measurements reveal that also in C,H,CH,C(CH,), and pO,NC,H,CH,C(CH,), the 'J(Clpso, CH,) coupling constant bears a value typical of this type of bonding (43.8 and 42.6 Hz, respectively). Thus, at variance with Lambert and Singer's observation, a slight increase in 'J(CC) coupling constants occurs on passing from So to C derivatives. This contradicts not only their experimental data but also conclusions concerning hyperconjugation in the neutral ground state.