This invention relates to the field of nucleic acid chemistry, more specifically to the field of compositions and processes that are nucleic acid analogs. More specifically, this invention relates to compositions that allow the sequencing of oligonucleotides by synthesis, and processes for sequencing by synthesis that exploit these compositions. Most specifically, the instant invention discloses compositions of matter that are 5'-triphosphates of ribo- and 2'-deoxyribonucleosides wherein the 3'-OH group is replaced by a 3'-ONHR group in the alpha configuration, wherein R is either a H or CH.sub.3 group. Also disclosed are these triphosphates where the nucleobase carries, via a linker, a reporter groups, such as a fluorescent species that can be used in single- or multi-copy DNA sequencing, or a tag that can be visualized by ultramicroscopy. Also disclosed are processes that use these compositions to do sequencing by synthesis.