C20H31

C20H31 is a chemical formula representing a hydrocarbon composed of twenty carbon atoms and thirty-one hydrogen atoms. Because the hydrogen count is odd for a neutral, closed-shell hydrocarbon, C20H31 is typically understood as a radical species or as an ion rather than a stable, non-radical molecule. Consequently, the formula alone does not determine a single structure.

In practice, many structural isomers can share the same C20H31 composition. The class of possible structures includes linear and branched aliphatic hydrocarbons with varying degrees of unsaturation, as well as cyclic or partially unsaturated systems. The exact arrangement of carbon and hydrogen atoms—whether the molecule is a radical at a particular carbon, contains one or more double bonds, or features rings—greatly influences properties such as reactivity and spectroscopy.

C20H31 commonly appears as a fragment or ion in analytical techniques such as mass spectrometry, especially in the study of larger hydrocarbon frameworks and terpenoid-related compounds. Identification of a species with this formula typically requires additional spectroscopic information (for example, tandem mass spectrometry, infrared, or nuclear magnetic resonance data) or comparison with known fragmentation patterns, since the formula alone is insufficient to pinpoint a unique structure.

Related concepts include hydrocarbon radicals and molecular ions, which may be produced by ionization or fragmentation of larger molecules. The formula highlights the limitation of relying on a single empirical composition to define structure, underscoring the need for complementary experimental data to determine precise connectivity and stereochemistry.