Nucleic acids—including DNA, RNA, and their constituent nucleotides in purified or synthetic form—fall under the residual subheading 293499 when not more specifically provided for. Synthetic oligonucleotides used as research reagents or therapeutic agents are typically classified here, though the specific form and purity may affect whether FDA review as a drug or biologic is also triggered.

Pure benzothiazole-ring compounds and their salts are classified under 293420 regardless of their intended use as rubber accelerators. Once a benzothiazole compound is formulated into a prepared rubber accelerator mixture or compounded with other ingredients, it may shift to the prepared rubber accelerator heading in the chapter on rubber. The key test is whether the article is a chemically defined compound or a preparation.