EN
For a (DF)-space E and a tensor norm α we investigate the derivatives $Tor^{l}_{α}(E,·)$ of the tensor product functor $E ⊗̃_{α} ·: 𝓕𝓢 → 𝓛𝓢$ from the category of Fréchet spaces to the category of linear spaces. Necessary and sufficient conditions for the vanishing of $Tor¹_{α}(E,F)$, which is strongly related to the exactness of tensored sequences, are presented and characterizations in the nuclear and (co-)echelon cases are given.