The convertible nucleoside 2-Fluoro-dI CEP allows the formation of N2-alkyl-dG residues in DNA for structural studies. After incorporation of this unit into an oligoribonucleotide by standard phosphoramidite chemistry, treatment with ammonia, methylamine, or a higher alkylamine, including one bearing a tethered functional group, leads to displacement of fluoride ion with resultant installation of a 2-amino group, i.e., producing a deoxyguanosine or an N2-alkyl-dG residue.