text: Usually, alkyl groups are attached to other atoms or groups of atoms. Free alkyls occur as neutral radicals, as anions, or as cations. The cations are called carbocations. The anions are called carbanions. The neutral alkyl free radicals have no special name. Such species are usually encountered only as transient intermediates. However, persistent alkyl radicals with half-lives "from seconds to years" have been prepared. Typically alkyl cations are generated using superacids and alkyl anions are observed in the presence of strong bases. Alkyl radicals can be generated by a photochemical reaction or by homolytic cleavage. Alkyls are commonly observed in mass spectrometry of organic compounds. Simple alkyls (especially methyl) are observed in the interstellar space as well.