A nucleotide or a salt thereof of Formula (IIIA): wherein X is a nucleobase or a tagged nucleobase; Y is -O-P(O)(OH)-[O-P(O)(OH)] z -OH or -O-P(O)(OH)-[O-P(O)(OH)] z -O-oligonucleotide, where z is 0 or an integer ranging from 1 to 5; R 1 is a bond, -CH 2 -, -C(O)-O-, -C(O)-NR a -, or -C(O)-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(O)-OR a , -C(O)-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(O)-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(O)-; 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)(OH)-[O-P(O)(OH)] z -OH or -O-P(O)(OH)-[O-P(O)(OH)] z -O-oligonucleotide, where z is 0 or an integer ranging from 1 to 5; R 1 is a bond, -CH 2 -, -C(O)-O-, -C(O)-NR a -, or -C(O)-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(O)-OR a , -C(O)-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(O)-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(O)-; 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. <EOS>