The use of thiols as nucleophiles in conjugation reactions is an increasingly popular reaction. In some ways thiols have similar properties to alcohols, however, sulfur is a third row element and thus the third level orbitals are larger than the valence orbitals for oxygen, which results in a weaker carbon–heteroatom bond. In addition, sulfur is significantly less electronegative than oxygen and bonding electrons have access to 3d orbitals. The result of this is a much more rich, complex and diverse chemistry for thiols as compared to alcohols. In addition the bond dissociation energy for an S–H bond is significantly less than for O–H. This weakening of the bond allows thiols to undergo facile oxidative coupling to disulfides. Thiols are also stronger acids than their alcohol analogues, and thus thiols are much more powerful nucleophiles, as sulfur is larger and more polarisable. In addition, the availability of the 3d orbitals assists in electron delocalisation. This rich chemistry has resulted in sulfur having an important role in technological applications