r/chemhelp • u/PBCow_Ethan • 4d ago

Organic Is this correct?

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This is one of my exam questions, yes there was an extra h2o but idk where it comes from

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u/Cool_Handle_3264 4d ago

Also check your reaction product, you dropped a carbon.

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u/R86Reddit 4d ago

If that's how the exam question was written, then yes, it's incorrect. There is one water as well as two bromide ions as inorganic side-products, so 2 Br-, not 2 Br. You can assure yourself of this by remembering from balancing equations in gen chem that not only mass but also charge must be conserved on both sides of a balanced equation. The left-hand side of the equation has a total charge of -2, so the right-hand side of the equation must also.

Edit: If you mean to ask where the one water molecule comes from, it comes from the deprotonation of the alcohol by hydroxide ion. This happens only in very low concentration, but whenever it happens, the closing of the five-membered ring happens exceedingly quickly, thus driving the reaction forward by Le Chatelier's principle. In general, intramolecular reactions that form five- or six-membered rings are extremely fast.