This invention relates to nucleoside, nucleotide, and oligonucleotide analogs that incorporate non-standard nucleobase analogs, defined to be those that present a pattern of hydrogen bonds to a paired nucleobase analog in a complementary strand that is different from the pattern presented by adenine, guanine, cytosine, and thymine. The invention is specifically concerned with nucleotide analogs that present the donor-donor-acceptor, hydrogen bonding patterns on pyrimidine analogs, and especially those that are analogs of ribonucleotides, including protected ribonucleotides suitable for phosphoramidite-based synthesis of RNA. The heterocycles on these nucleoside analogs are aminopyridones that have electron withdrawing groups attached to the position analogous to the 5-position of the ring in standard pyrimidines, including nitro, cyano, and carboxylic acid derivatives.