C2H5

C2H5 is the chemical formula representing two carbon atoms and five hydrogen atoms. In organic chemistry it most often denotes the ethyl group, a two‑carbon alkyl substituent with the structure CH3–CH2–. When considered as a substituent, it is written as -C2H5; as a free radical, the species is C2H5•, with an unpaired electron on the terminal carbon.

The ethyl group is a primary alkyl group and is nonpolar, contributing a two‑carbon tail to larger molecules and increasing hydrophobicity. The ethyl radical, C2H5•, is highly reactive and typically short‑lived, forming bonds at available sites in radical reactions. In many contexts, the neutral substituent is the relevant form, while C2H5• appears in kinetic or gas‑phase mechanisms.

Occurrence and uses: Ethyl groups are common in organic synthesis and in a wide range of compounds. Ethyl substituents appear in esters such as ethyl acetate (CH3COOCH2CH3) and in ethers such as diethyl ether (CH3CH2–O–CH2CH3). Ethyl fragments also arise as characteristic pieces in mass spectrometry fragmentation patterns of larger molecules.

Nomenclature and related forms: The ethyl group derives from ethane by removing one hydrogen, yielding the formula C2H5–. Related species include the ethyl radical C2H5• and various ethyl derivatives where the group is attached through the carbon chain to another moiety.

In summary, C2H5 most often denotes the ethyl group or radical, a fundamental two‑carbon fragment in organic chemistry with widespread synthetic and analytical relevance. Approximately 29.06 g/mol is the nominal molecular mass for the C2H5 unit.