AbstractThe ethane structure‐related molecules Cl3CSi(CH3)3 (1), (H3C)3CSiCl3 (2), and (CH3)3CSi(CH3)2Cl (3) crystallize from the melt to an orientational disordered body centered cubic (plastic) phase I, Im3m, Z = 2. By DTA/DSC the following thermodynamic data have been determined (temperatures in K, ΔH in kJ mol−1). (1): Tm = 405.3; ΔHm = 7.36; ΔSm/R = 2.17; TI,II = 285.5; ΔHI,II = 11.16; ΔSI,II/R = 4.68. (2): Tm = 373.4; ΔHm = 6.69; ΔSm/R = 2.13; TI,II = 206.4; ΔHI,II = 6.01; ΔSI,II/R = 3.45. (3): Tm = 358.1; ΔHm = 5.66; ΔSm/R = 1.87; TI,II = 203.6; ΔHI,II = 7.75; ΔSI,II/R = 4.51. At 293 K the lattice constants of the bcc unit cells are (1): 796.6 (2) pm (303 K), (2): 794.5 (7) pm, (3): 803.6 (9) pm.(1) Shows a two line 35Cl NQR spectrum (νi in MHz, T = 77 K) with ν1 = 37.213, ν2 = 37.033, fade out temperature Tf = 253 K; (2): Doublet, ν1 = 19.060, ν2 = 18.260, Tf = 177 K; (3): ν = 16.786, Tf = 200 K.The 1H‐NMR line width and the second moment M2 (1H) of (2) show the orientationally disordered state above TI,II, hysteresis in TI,II, the freezing‐in of the t‐butyl group rotation below TI,II, and a freezing‐in of the individual CH3 group rotation below 100 K.