Wiktionary
spiropentane
n. (context organic compound English) The simplest triangulane hydrocarbon, C5H8, consisting of two spiro-linked cyclopropane rings
Wikipedia
Spiropentane
Spiropentane is a hydrocarbon with formula CH. The simplest spiro-connected cycloalkane. It took several years after the discovery in 1887 until the structure of the molecule was determined.