The bond energy (BE) of CC in CH3-CH3 with respect to geometry frozen fragments follows a sigmoidal increase as a function of the θ = HCC pyramidalization angle. Using dynamic orbital forces as a BE index, the same behaviour as a function of a unique <θ> parameter, mean angle of the substituents, is found for 24 single CC bonds in various hydrocarbons. Thus the <θ> parameter appears as a straightforward and robust index of the geometrical constraints which can either strengthen or weaken a bond. This way, CC sigma bonds can be easily classified into weak "inverted" bonds for <θ> < 90° (eg. in [111]propellane and bicyclobutane), "direct" (or "normal") bonds for 90° < <θ> < 120° (eg. ethane), and strong "superdirect" bonds for <θ> > 120° (eg. in tetrahedryltetrahedrane and butadiyne).