Nuclear-spin polarization in electron-transfer reactions of amines

Chemically induced dynamic nuclear polarization (CIDNP) observed during electron transfer (ET) reactions of tertiary amines such as DABCO (1) or Et ₃N (2) with a wide range of electron acceptors support the involvement of amine radical-cations (e.g., 1^.+ or 2^.+) as key intermediates. Radical ions such as 2^.+ may be deprotonated, generating neutral aminoalkyl radicals (e.g., 2^.). When generated by reaction with an electron acceptor of energetically low triplet state such as naphthalene (¹Naph*), the resulting pair 2^.+/ Naph^.- reacts mostly by reverse electron transfer (RET) from triplet pairs populating the naphthalene triplet state.