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This is the reactant molecule which undergoes wurtz reaction. All possible products are- enter image description here

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What will be the most favorable in all of these? In my opinion that the last one should not be the one because it forms a three member ring which is quite unstable due to angle strain. Still it is the answer to the question.

why any other molecule is not the major product?

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    $\begingroup$ According to doi.org/10.1021/jo01118a042, it is indeed the last one, spiropentane (approx. 50 % conversion). You can foster the search process knowing your precursor's more common name (pentaerythrityl tetrabromide) and CAS number (3229-00-3). $\endgroup$
    – andselisk
    Nov 17 '21 at 9:05
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    $\begingroup$ @ashank Yes, it is a strained species, but there are very many cyclopropanes known so clearly the strain is not a determining factor. $\endgroup$
    – Waylander
    Nov 17 '21 at 9:27
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    $\begingroup$ @ashank No prob, this was just a published confirmation for the given answer. It doesn't seem authors provide an in-depth explanation as to why spiropentane is favored, so your question remains. $\endgroup$
    – andselisk
    Nov 17 '21 at 10:21
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    $\begingroup$ Spiropentane is preferred, because it does not contain any bromine atom. If enough sodium is available, all bromine atoms will be transformed into $\ce{NaBr}$, so that the final product must be a hydrocarbon with $5$ atoms, or a polymer. $\endgroup$
    – Maurice
    Nov 17 '21 at 10:50
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    $\begingroup$ @ashank Exactly so. That is why chemistry remains an experimental science. You cannot predict the outcome of many reactions so you have the run the experiment $\endgroup$
    – Waylander
    Nov 17 '21 at 11:22

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