Organic Chem Questions: H3O+ , H+, OH

[pandalove89]

Hey guys,

this may sound really stupid...


But during reactions if the last step is H3O+, H+, or OH, what does it mean?


I understand sometimes its coupled with certain other reactants, but sometimes I get really stuck.

For example say there is reactant 1 (---> 1. ) then 2 (--> 2. ) but then the last step it says (3. --H3O+-->)

I just get stuck.

Any suggestions?

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[FROGGBUSTER]

It could be a way to simply protonate something, or it could actually be a reactant that for example transforms an acyl halide into a carboxylic acid.

 

[PooyaH]

H3O+ or H+ create a reducing environment assuring that the end product will become protonated.

 

[pandalove89]

Okay for example, if you have ketone group with a double bond somewhere in it and react it with 1) LiAlH4 ---> 2) H3O+

1st: obviously the Oxygen on the ketone group will get reduced to a secondary alcohol.

2nd: So in this case wouldnt the H3O+ somehow protonate either the newly formed alcohol or even protonate carbons on the double bond to make it a single bond?

 

[indigenoustw]

LiAlH4 is like a hydride anion. It attacks the electrophilic carbonyl carbon, so the oxygen will eventually bear a negative charge. That negative charge formed is stabilized by having Li+ around. So you will see ----O- Li+ from the first step. H3O+ will protonate that oxygen to give you the alcohol.

 

[needzmoar]

Okay for example, if you have ketone group with a double bond somewhere in it and react it with 1) LiAlH4 ---> 2) H3O+

1st: obviously the Oxygen on the ketone group will get reduced to a secondary alcohol.

2nd: So in this case wouldnt the H3O+ somehow protonate either the newly formed alcohol or even protonate carbons on the double bond to make it a single bond?

No, the negatively charged tetrahedral will get neutralized (assuming 1:1 molar equivalence)