[Miss Atom]

In the reaction of HBr with cyclohexenone would the ketone portion cause the -Br to be attached meta? Or is there done other property at work that would cause ortho or para?

[sjb]

In the reaction of HBr with cyclohexenone would the ketone portion cause the -Br to be attached meta? Or is there done other property at work that would cause ortho or para?

At a simple level, ortho, meta and para only really refer to substituents on a benzene ring, but they do make a sort of sense here. What is the polarity of both HBr and cyclohexenone?

[Miss Atom]

HBr is polar.

What I know: "cyclohexenone can be 1,4-addition (Michael addition), or with Grignard reagents 1,2-addition, ie, with attack of the nucleophile at the carbonyl carbon atom."

I can't find anything about how cyclohexenone reacts with HBr. I just assumed it was some sort of addition.

[opsomath]

This is an odd question.

The reason it's odd is because usually, HBr addition to alkenes is kept simpler. Either plain alkenes with no other groups, or conjugated alkenes. This is because it's actually, in practice, kind of a crap reaction. It is difficult to execute cleanly in the lab. In the case of a more complex reactant, it actually gets even worse; this mixture can cause cyclohexenone to react with itself to form what we usually call "brown crap" in an acid-catalysed reaction.

So, I have to ask, is this actually from an assignment or did you make it up?

To the extent that it happens, HBr will add conjugate to the molecule, making 3-bromocyclohexanone.

[Miss Atom]

From an actual assignment. I'm glad someone else thought 3 addition as well because I've been pulling my hair out trying to think this over.