A nucleotide or a salt thereof of Formula (IIIA): wherein X is a nucleobase or a tagged nucleobase; Y is -O-P -[O-P] z -OH or -O-P -[O-P] z -O-oligonucleotide, where z is 0 or an integer ranging from 1 to 5; R 1 is a bond, -CH 2 -, -C -O-, -C -NR a -, or -C -R x -; R 2 and R 3 are each independently H, a saturated or unsaturated Ci - C 6 alkyl group, a C 5 - C 6 aryl or heteroaryl group, a halogen, -[(C(R a)(R b)) p -O] q -(R a), -C -OR a, -C -N(R a)(R b), -(C(R a)(R b)) n -N + C -, -CN, or -NO 2; R 4 is a bond, a substituted or unsubstituted 5- to 7-membered aryl group, - CH=CH-, a substituted or unsubstituted 5- or 6-membered heterocycloalkyl group, or -O-C -aryl-; R 5 is -(C(R a)(R b)) n -N 3, -(C(R a)(R b)) n -N + C -, -(C(R a)(R b)) n -CN, a 5- to 8-membered cycloalkyl group comprising two sulfur atoms positioned 1, 3 relative to each other, or a group having the structure: Z 1 and Z 2 are independently H, a C 1 - C 4 alkyl group, or a 5- to 6-membered aryl group optionally substituted with one or more hydroxyl groups; Q 1 and Q 3 are each independently a bond, -C(R e)(R f)-, or -C -; Q 2 is a bond, o-phenylene, or -[C(R e)(R f)] w -, where w is 1 or 2; R a and R b are each independently H or a saturated C 1 - C 6 alkyl group; R e and R f are independently H, methyl, ethyl, isopropyl, or a substituted or unsubstituted 5- or 6-membered aryl group; R x is a substituted or unsubstituted 5- or 6-membered aromatic group or heteroaromatic group; n is 0 or an integer ranging from 1 to 3; and p and q are each independently zero or an integer ranging from 1 to 3; provided that when R 1 and R 4 are both bonds and when R 2 and R 3 are both H, then R 5 is not an azide. X is a nucleobase or a tagged nucleobase; Y is -O-P -[O-P] z -OH or -O-P -[O-P] z -O-oligonucleotide, where z is 0 or an integer ranging from 1 to 5; R 1 is a bond, -CH 2 -, -C -O-, -C -NR a -, or -C -R x -; R 2 and R 3 are each independently H, a saturated or unsaturated Ci - C 6 alkyl group, a C 5 - C 6 aryl or heteroaryl group, a halogen, -[(C(R a)(R b)) p -O] q -(R a), -C -OR a, -C -N(R a)(R b), -(C(R a)(R b)) n -N + C -, -CN, or -NO 2; R 4 is a bond, a substituted or unsubstituted 5- to 7-membered aryl group, - CH=CH-, a substituted or unsubstituted 5- or 6-membered heterocycloalkyl group, or -O-C -aryl-; R 5 is -(C(R a)(R b)) n -N 3, -(C(R a)(R b)) n -N + C -, -(C(R a)(R b)) n -CN, a 5- to 8-membered cycloalkyl group comprising two sulfur atoms positioned 1, 3 relative to each other, or a group having the structure: Z 1 and Z 2 are independently H, a C 1 - C 4 alkyl group, or a 5- to 6-membered aryl group optionally substituted with one or more hydroxyl groups; Q 1 and Q 3 are each independently a bond, -C(R e)(R f)-, or -C -; Q 2 is a bond, o-phenylene, or -[C(R e)(R f)] w -, where w is 1 or 2; R a and R b are each independently H or a saturated C 1 - C 6 alkyl group; R e and R f are independently H, methyl, ethyl, isopropyl, or a substituted or unsubstituted 5- or 6-membered aryl group; R x is a substituted or unsubstituted 5- or 6-membered aromatic group or heteroaromatic group; n is 0 or an integer ranging from 1 to 3; and p and q are each independently zero or an integer ranging from 1 to 3; provided that when R 1 and R 4 are both bonds and when R 2 and R 3 are both H, then R 5 is not an azide.