This invention is directed to oligomers composed of 2′-3′-seco-nucleomonomers and nucleotides or modified nucleotides, wherein the oligomer can be a microRNA and include from one to five 2′-3′-seco-nucleomonomers. The oligomers can have a sequence that is complementary to a target nucleotide sequence and be used for affecting the regulation of gene expression. Among other things, the oligomers can provide reduced off target effects.