The first observation of a muonium–carbonyl adduct with a negative muon coupling constant

Abstract

Muonium atom addition to cyclopent-4-ene-1,3-dione I leads to the adduct radical II; in contrast with all other muonium adducts of carbonyl (C[double bond, length half m-dash]O) compounds so far studied, in which the isotropic muon coupling is of positive sign, the temperature dependence of the muon coupling in II reveals that its sign is negative; this may be explained as a consequence of the electronic ‘push–pull’ interaction within the MuO–C–C[double bond, length half m-dash]C–C[double bond, length half m-dash]O system, which reduces the out-of-plane vibrational amplitude of the muon by increasing the MuO–C/MuO[double bond, length half m-dash]C partial π-bond character.

References

1. R. M. Macrae, C. J. Rhodes, K. Nishiyama and K. Nagamine, Chem. Phys. Lett., 1996, 259, 103.
2. C. J. Rhodes and M. C. R. Symons, Magn. Reson. Chem., 1996, 34, 631.
3. D. Buttar, R. M. Macrae, B. C. Webster and E. Roduner, J. Chem. Soc. Faraday Trans., 1990, 86, 220.
4. R. M. Macrae, B. C. Webster and E. Roduner, Muon Studies in Solid State Physics, IOP Short Meetings no. 22, 1988, p. 95.
5. A. Hill, S. F. J. Cox, R. de Renzi, C. Bucci, A. Vecli and M. C. R. Symons, Hyperfine Interact., 1984, 17–19, 815.
6. S. F. J. Cox, D. A. Geeson, C. J. Rhodes, E. Roduner, C. A. Scott and M. C. R. Symons, Hyperfine Interact., 1986, 32, 763.
7. K. Venkateswaran, R. F. Kiefl, M. V. Barnabas, J. M. Stadlbauer, B. W. Ng, Z. Wu and D. C. Walker, Chem. Phys. Lett., 1988, 145, 289.
8. M. Heming, E. Roduner, B. D. Patterson, W. Odermatt, J. Schneider, H. Baumeler, H. Keller and I. M. Savic, Chem. Phys. Lett., 1986, 128, 100.
9. D. Buttar, R. M. Macrae, B. C. Webster and E. Roduner, Hyperfine Interact., 1990, 65, 927.
10. G. M. Aston, J. A. Stride, U. A. Jayasooria and I. D. Reid, Hyperfine Interact., 1997, 106, 157.
11. C. J. Rhodes, C. S. Hinds and I. D. Reid, J. Chem. Soc., Faraday Trans., 1996, 92, 4265.
12. C. J. Rhodes, I. D. Reid and R. A. Jackson, Hyperfine Interact., 1997, 106, 193.
13. D. C. Walker, Muon and Muonium Chemistry, Cambridge University Press, Cambridge, 1983.
14. There is but one example of a carbon centred radical with a negative muon coupling, Me₃SiCHMu, which arises from the unique α-position of the muon which, therefore, receives spin density from spinpolarisation of the C–Mu bond; B. Addison-Jones, P. W. Percival, J.-C. Brodovitch and F. Ji, Hyperfine Interact., 1997, 106, 143.
15. E. Roduner, The positive muon as a probe in free radical chemistry. Potential and limitations of the µSR techniques, Lecture notes in chemistry, vol. 49. Heidelberg, Springer, 1988.