In a Wurtz reaction, is the intermediate formed a carbanion or a free radical. And if can assume both mechanisms to be true, how can we decide the reactivity of a tertiary halide?
I think both mechanisms are valid. As far as I know, both are supported by some experimental evidence. By-products, like alkanes(other than the expected one) and alkenes, can be explained by the free radical mechanism. On the other hand, the formation of Organometallic compounds can be verified by the ionic mechanism.
The essential thing to note is that the mechanism involves a SN2 step. And because of that sterically hindered alkyl halides, like tertiary alkyl halides, instead of giving a substitution product yield an elimination product and you get an alkene.
A mechanism is only a hypothesis which can explain a particular reaction. Wurtz reaction can be explained by both ionic and free radical mechanism.
Well I personally think it is better explained by free radical mechanism, as using this mechanism, you can easily analyse all the products formed, whether it be symmetrical compound formed from same alkanes, or an unsymmetrical compound.