The homologous hydrocarbon series R ₄ C is known for R=Me as neopentane and for R=Et as 3,3-diethylpentane. The next homologue, R=* ⁱ *Pr bis(3,3-isopropyl)-2,4-dimethylpentane is also a known molecule[cite]10.1002/1521-3773(20010105)40:1%3C180::AID-ANIE180%3E3.3.CO;2-B[/cite] for which a crystal structure has been reported (DOI: https://doi.org/10.5517/cc4wvnh). The final member of the series, R= ^t butyl is unknown.