C3H7

C3H7 is a chemical formula representing a three-carbon hydrocarbon fragment with seven hydrogens. It is not a standalone neutral molecule, but denotes propyl-type fragments that can exist as radicals, cations, or, less commonly, anions in suitable environments. The two principal structural isomers are the n-propyl and the isopropyl forms.

As radicals, they are written as C3H7•: the n-propyl radical CH3-CH2-CH2• and the isopropyl radical (CH3)2CH•. Corresponding cations are C3H7+: primary propyl cation CH3-CH2-CH2+ and secondary propyl cation (isopropyl cation) (CH3)2CH+. Propyl anions, while theoretically possible as CH3-CH2-CH2−, are extremely uncommon and highly unstable under ordinary conditions.

In practice, C3H7 fragments are encountered in mass spectrometry as common fragments of propane and larger hydrocarbons, often appearing at a mass-to-charge ratio of 43 (m/z 43). They also arise in reaction mechanisms involving radical propagation or carbocation rearrangements, such as during alkane activation or during fragmentation pathways of alkyl-containing molecules.

The term propyl is used in organic nomenclature to describe a three-carbon substituent; specifying prefixes or descriptors (n- or isopropyl) clarifies the exact attachment and structure. Because the radicals and cations are reactive, their lifetimes are typically short in most environments. C3H7 units therefore play a key role in petrochemical processing, analytical techniques, and various areas of synthetic organic chemistry.