The FT-microwave spectrum of germylcyclohexane, c-C6H11GeH3, has been recorded, and more than 40 transitions for the Ge-70, Ge-72, and Ge-74 isotopomers (isotopologues) have been assigned for the chair-equatorial conformer. The heavy atom adjusted r(0) structural parameters have been determined [distances, C-gamma-C-delta = 1.533(3) angstrom, C-alpha-C-beta = 1532(3) angstrom, C-alpha-C-beta = 1.540(3) angstrom, C-alpha-Ge = 1.957(3) angstrom; angles, angle C gamma C delta C beta = 111.2(5)degrees, angle GeC alpha C beta = 111.1(5)degrees, with the dihedral angle angle C gamma C delta C beta C alpha = 55.6(10)degrees]. Raman and/or infrared spectra of gas, liquid, and solid germylcyclohexane have been recorded. The temperature dependency of the Raman spectrum of the conformer pair 712 (equatorial)/683 (axial) cm(-1) gives an enthalpy difference of 453 +/- 38 cm(-1) (1.30 +/- 0.11 kcal/mol) with the chair equatorial conformer the more stable form. At ambient temperature, the abundance of the axial conformer is 11 +/- 1%. Substituent effects on the enthalpy difference and structure of monosubstituted cyclohexanes are discussed for a number of molecules.