Density functional calculations have been carried out on Cp2Sc-R (R= H, methyl, ethyl, propyl, vinyl, and acetylide). Geometry optimizations reveal an agostic interaction for R= ethyl, whereas methyl and propyl are bound to the metal center without agostic interactions. The Sc-R bond energies are calculated as De(Sc-acetylide) = 540 kJ mol-1 > De(Sc-H) = 340 > De(Sc-vinyl) = 338 > De(Sc-methyl ) = 295 > De(Sc-ethyl) = 283 > De(Sc-propyl ) = 240. A study on the s-bond metathesis reaction (I): Cp2Sc-R + H-R' Æ Cp2Sc-R' + H-R, reveal the following reaction enthalpies, DHI (R, R'), in kJ mol-1 : DHI(CH3, acetylide) = -128 < DHI(H, acetylide) = -86 < DHI(CH3, H) = -28 < DHI(CH3, vinyl) = -26 < DHI(H, vinyl) = 16. The reaction (I) proceeds from an adduct (a) between Cp2Sc-R and H-R' over a kite shaped four-center transition state (b) with a Sc-R-H-R' core to an adduct (c) between Cp2Sc-R and H-R'. The activation energies, DH|S(#,I) (R, R'), are calculated in kJ mol-1 as: DH|S(#,I) (H, acetylide) = -29 < DH|S(#,I) (H, H) = -7 < DH|S(#,I) (CH3, acetylide) = -4 < DH|S(#,I) (CH3, H) = 8 < DH|S(#,I) (H, vinyl) = 14 < DH|S(#,I) (CH3, vinyl) = 39 < DH|S(#,I) (CH3, CH3) = 45. The activation energies increase with the number of vinyl and methyl groups in the Sc-R-H-R' core as the directional s-orbital on these groups are unable to maintain optimal interactions with both neighbors in the Sc-R-H-R' core. The transition states for reactions with negative activation energies are below the reactants in energy but still above the adduct (a). The formally forbidden [2s + 2s] reaction is facilitated by a pool of s, p, and d type orbitals on scandium which maintain optimal interactions with the neighboring groups throughout the reaction.