Single crystals of the title compounds, C12H27P (1), C12H27P (2), and C9H27PSi3 (3), were grown in capillaries at low temperature using zone-melting techniques [Brodalla, Mootz, Boese & Osswald (1985). J. Appl. Cryst. 18, 316-319]. The molecular and crystal structures of all three compounds were determined at 102 K. Compound (1) has a pseudo-mirror plane and C-P-C angles between 100.5 (1) and 102.7 (1)degrees. Compound (2) has a pseudosymmetric threefold rotation axis and C-P-C angles of 107.1 (1), 107.4 (1) and 107.8 (1)degrees. Isomorphous compound (3) has Si-P-Si angles between 105.8 (1) and 106.5 (1)degrees.