2901.24 - Buta-1,3-diene and isoprene:

This HTS category, 2901.24, specifically covers acyclic hydrocarbons that are unsaturated and belong to the "other" sub-group within butenes and their isomers. This means it encompasses unsaturated hydrocarbons with four carbon atoms that do not fit into the more specific classifications for ethylene, propene, or butene and its isomers. The primary distinction from its siblings lies in the number of carbon atoms and the presence of double bonds; while ethylene (C2), propene (C3), and butenes (C4) are covered elsewhere, this category captures other four-carbon unsaturated acyclic hydrocarbons and importantly, the key monomers buta-1,3-diene and isoprene.

Within this grouping, a crucial distinction is made between buta-1,3-diene and isoprene themselves, and other unsaturated hydrocarbons that might otherwise fall into this broad "other" category. Buta-1,3-diene is characterized by two conjugated double bonds, making it a vital building block for synthetic rubber and plastics. Isoprene, also known as 2-methylbuta-1,3-diene, is structurally similar with conjugated double bonds but includes a methyl group, serving as the monomer for natural rubber and a component in synthetic polymers.

Therefore, subcategories within 2901.24 are established to provide more granular classification for these important chemicals. The primary subdivisions differentiate buta-1,3-diene from isoprene, recognizing their distinct chemical structures and significant industrial applications. This allows for precise tariff application based on whether the specific product is buta-1,3-diene or isoprene, or another unsaturated acyclic hydrocarbon meeting these criteria but not falling into the more precisely defined sibling categories.