Described are 5′-cyclo-phosphonate modified nucleotides, and oligonucleotides, such as interference (RNAi) agents, containing 5′-cyclo-phosphonate modified nucleotides. The RNAi agents having either double-stranded or single-stranded oligonucleotides described herein comprising 5′cyclo-phosphonate modified nucleotides are useful in modulating gene expression as well as therapeutic, diagnostic, target validation, and genomic discovery applications. The RNAi agents and single-stranded antisense oligonucleotides comprising 5′-cyclo-phosphonate modified nucleotides are useful in the treatment of diseases or conditions that respond to inhibition of gene expression or activity in a cell, tissue, or organism.