noctadecyl

Noctadecyl is a chemical term used to denote the straight-chain alkyl substituent with 18 carbon atoms, commonly referred to in its systematic form as octadecyl or n-octadecyl. The name noctadecyl is largely historical or non-systematic; octadecyl is the preferred IUPAC designation.

The noctadecyl group is a long, unbranched hydrocarbon tail. As a substituent, it imparts pronounced hydrophobic character to the molecules to which it is attached and tends to reduce water solubility while increasing affinity for nonpolar solvents. The presence of an 18-carbon chain often classifies the compound as a waxy or lipophilic material at ambient conditions, with properties that vary with branching and functional groups.

In chemistry and materials science, octadecyl/noctadecyl groups are used to tailor surface properties and solubility. Examples include octadecylsilane coupling agents and octadecyltrichlorosilane for forming hydrophobic self-assembled monolayers, as well as long-chain alkyl esters and surfactants. In cosmetics and personal care, octadecyl derivatives appear as emollients, thickeners, or stabilizers in formulations.

Safety and handling depend on the specific compound bearing the octadecyl group. Long-chain alkyl derivatives can be irritants or flammable in some contexts and are typically handled with standard laboratory or industrial hygiene practices. Noctadecyl should be treated as a descriptor for an 18-carbon tail rather than a standalone chemical, with precise properties defined by the attached moiety.

See also: octadecyl, n-octadecyl, cetyl, stearyl, octadecyltrichlorosilane.