Low and zero field stimulated nuclear polarization in cyclic ketones

13C stimulated nuclear polarization (SNP) in acyl-alkyl biradicals has been investigated at a low magnetic field B0. For carbons in the carbonyl position, which have a strong hyperfine interaction (hfi), a significant SNP effect is observed at low fields B0 < hfi, in contrast to carbons in the α-position with smaller hyperfine coupling. A qualitative analysis using a two-state biradical model shows that this effect has a strong dependence onthe non-spin selective channels of the biradical decay.