Resins are usually mixtures of organic compounds. Acid rain can damage infrastructures containing calcite or certain other solid chemical compounds. Such series are useful for determining necessary solvents needed for chromatography of chemical compounds. Filtered air includes trace amounts of many other chemical compounds. Alkanes are only weakly reactive with most chemical compounds. Beeswax is a tough wax formed from a mixture of several chemical compounds. Both saturated (alicyclic) compounds and unsaturated compounds exist as cyclic derivatives. The toxicity of quaternary ammonium compounds, which are antibacterial and antifungal, varies. Air concentrations of volatile organic compounds and PAHs never exceeded permissible exposure levels. Food also contains many organic arsenic compounds. It is also one of the chemical compounds found in castoreum. One study identified 40 different phenolic compounds. It is nevertheless important in understanding the nomenclature conventions of inorganic compounds. They often are prepared by nitration of the substituted aromatic compounds followed by reduction. Tannins are congeners found in wine in the presence of phenolic compounds.