How many molar equivalents of reagent will react?

[Jay0689]

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I've been assuming just one mole of reagent will react unless the problem says otherwise, but not so for Destroyer OC #41:

A cyclic ester reacts with grignard. I assumed just one mole of grignard would attack the carbonyl, but the answer says that two moles of grignard react and open up the ring. Thus the two oxygens in the cyclic ester are made into alcohol groups.

How do you deal with problems when a different product (possibly more stable) would form if two moles of the reagent reacted?

 

[Bis-GMA111]

yea that one pissed me off

you're supposed to assume 2 equivalents of grignard if you're given an ester, a carboxylic acid, or acyl chloride

 

[Jay0689]

Haha yea I moved on and then just two seconds ago saw that explanation in a later solution! I wonder how many people did the same thing. Thanks!

 

[spoog74]

I've been assuming just one mole of reagent will react unless the problem says otherwise, but not so for Destroyer OC #41:

A cyclic ester reacts with grignard. I assumed just one mole of grignard would attack the carbonyl, but the answer says that two moles of grignard react and open up the ring. Thus the two oxygens in the cyclic ester are made into alcohol groups.

How do you deal with problems when a different product (possibly more stable) would form if two moles of the reagent reacted?

exactly what predent said. WHENEVER you see an ester and a grignard, assume 2 moles of the nucleophile add on.