2931.49.00.55 - Containing a phosphorus atom to which one methyl, ethyl, n-propyl or isopropyl group is bonded but no further carbon atoms

This HTS code, 2931.49.00.55, specifically classifies organic phosphorus compounds where a phosphorus atom is bonded to one methyl, ethyl, n-propyl, or isopropyl group, and no other carbon atoms. This precise structural requirement differentiates these compounds from more complex organophosphorus derivatives. The focus is on the limited alkyl substitution directly attached to the phosphorus atom, excluding any further carbon chain extensions from that phosphorus.

Unlike the sibling category 2931.49.00.80 ("Other"), which would encompass a broader range of non-halogenated organophosphorus derivatives that do not meet the specific substitution criteria of this code, 2931.49.00.55 is highly restrictive. It targets substances like trimethyl phosphine or triethyl phosphine where the phosphorus atom has a specific, limited alkyl bonding profile. Classification into this category hinges on verifying the exact number and type of carbon groups directly bonded to the phosphorus atom.

As this is a leaf node within the HTS, there are no further subcategories. Therefore, the classification is definitive once the structural criteria are met. Importers and exporters should meticulously examine the chemical structure of their organophosphorus compounds to ensure accurate classification under this specific code, paying close attention to the direct bonding of carbon atoms to the phosphorus.