Orgo destroyer 2010 #33

[flin5845]

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The problem is basically 2 cyclohexane connected together with a carbonyl group coming off of 1 of the carbons. (sorry I dont know how to name this). But anyways the question wants to know the product if reacted with Cl2(xs) and H3O+

So this is a halogantion of a ketone under ACIDIC conditions. In my orgo class we learned that if you are doing halagonation under ACIDIC conditions, you well get a mono addition (even with excess) at a alpha carbon by going through the enol.

If the reaction was under BASIC conditions, going through the enolate, we would get addition at every alpha hydrogen.

The answer states that a chlorine would be added to every alpha position under acidic conditions.....Is this true under ACIDIC conditions?

 

[molar3]

The problem is basically 2 cyclohexane connected together with a carbonyl group coming off of 1 of the carbons. (sorry I dont know how to name this). But anyways the question wants to know the product if reacted with Cl2(xs) and H3O+

So this is a halogantion of a ketone under ACIDIC conditions. In my orgo class we learned that if you are doing halagonation under ACIDIC conditions, you well get a mono addition (even with excess) at a alpha carbon by going through the enol.

If the reaction was under BASIC conditions, going through the enolate, we would get addition at every alpha hydrogen.

The answer states that a chlorine would be added to every alpha position under acidic conditions.....Is this true under ACIDIC conditions?

yoooo i had the same question when i was doing this problem!! and i learned that u would add excess under BASIC conditions too, not acidic. and even chad says do it under basic conditions, very rareley if ever under acidic conditions. soooo i dunno either.......😱
+1

 

[ROCOCO8]

Hey I am coming across this problem... did anyone else come to the same conclusion? I also thought there's only addition of Cl at every alpha H if Cl2 was added under basic conditions, not acidic.

Is destroyer wrong?

 

[Chrono]

which question is this (number?) and which edition of destroyer are u guys using

 

[Dotoday]

This can work. It depends on what textbook you are using. Some textbooks do allow you to put excess Cl2 under acidic conditions across every alpha carbon, some say no.

Sent from my MB855 using Tapatalk

 

[ROCOCO8]

It's #33 from the 2010 edition

 

[Molarcule]

Yes, with Ketone and Aldehydes (with the exception for Formaldehyde) under basic and acidic conditions with the reaction of Cl2 and Acid, all the hydrogens would be replaced by the Cl2. The reason for this is because with every addition of Cl the product would be more reactive than the reactant thus every alpha hydrogen will be replaced.

 

[ROCOCO8]

alright. thank you!

 

[joemario]

Yes, with Ketone and Aldehydes (with the exception for Formaldehyde) under basic and acidic conditions with the reaction of Cl2 and Acid, all the hydrogens would be replaced by the Cl2. The reason for this is because with every addition of Cl the product would be more reactive than the reactant thus every alpha hydrogen will be replaced.

Is that true for bromine too?

 

[Meat Gyver]

In the case of acid-catalyzed halogenation, the rate determining step is enolization (independent of initial concentration of halogen). Once the initial halogenation is complete, you added an electron withdrawing group to your compound, and the electron withdrawing power of the halogen makes the carbonyl less basic than it originally was. As a result, that makes protonation more difficult than in the original carbonyl compound (or in other words, more difficult to make the enol - so you just made the rate limiting step even slower and forming the enol is less favorable). Therefore, the singly halogenated product is not attacked by additional halogens until the starting reactant has been used up.

So theoretically you CAN replace all the alpha hydrogens via acid catalyzed alpha halogenation, but it would be very unfavorable and slow.

If you were to react the same compound with something that wasn't electron withdrawing under acidic conditions, then you can expect to have all the alpha hydrogens replaced.


Just to add: The ketone is acting as the nucleophile, and with any electron withdrawing group, it will decrease nuc. strength of the nucleophile. Cl is not an activator, thus it doesn't increase nuc. strength/reactivity.