(one for H-FAU_16H, the other for H-FAU_32H_1_3, they are labelled with asterisks in Table ). However, these configurations are energetically less favourable than those where all significant interactions occur within a single 12MR. This indicates that the inclusion of different proton arrangements within one ring may be sufficient to cover the most relevant low-energy bonding situations for a relatively simply and rigid molecule like 5-FU.