Microwave Spectrum of Germacyclopentane

The microwave spectrum of four Ge isotopic species of the five‐membered heterocycle germacyclopentane (C₄H₁₀Ge) has been investigated in the region 8–22 GHz. Rotational constants for the ground state of the ⁷⁴Ge species are: $\text{A\hspace{0.17em}=\hspace{0.17em}5323.7}$ , $\text{B\hspace{0.17em}=\hspace{0.17em}2842.20}$ , $\text{C\hspace{0.17em}=\hspace{0.17em}2041.52}\mathrm{MHz}$ . From excited states assigned to the lowest ring‐deformation mode, a lower limit of about 500 cm⁻¹ has been estimated for the barrier to pseudorotation. The molecule is found to be permanently twisted into a C₂ conformation with a twist angle of 18°, and $\angle \mathrm{CGeC}\text{\hspace{0.17em}=\hspace{0.17em}98°}$ , $\angle \mathrm{GeCC}\text{\hspace{0.17em}=\hspace{0.17em}106°}$ , and $\angle \mathrm{CCC}\text{\hspace{0.17em}=\hspace{0.17em}115°}$ . Stark‐effect measurements give a dipole moment of 0.665 ± 0.007 D. For the ⁷³Ge species, the nuclear quadrupole coupling constants are found to be ${\chi }_{\mathrm{aa}}\text{\hspace{0.17em}=\hspace{0.17em}15.89}\mathrm{MHz}$ , ${\chi }_{\mathrm{bb}}\text{\hspace{0.17em}=\hspace{0.17em}−10.29}\mathrm{MHz}$ , ${\chi }_{\mathrm{cc}}\text{\hspace{0.17em}=\hspace{0.17em}−5.60}\mathrm{MHz}$ .