Ochem Destroyer question

[DSNCSUN]

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You have phenyl ethanone and use reactants Excess D2O and DCl (catalytic). Apparently reaction occurs at the alpha position. What is this reaction?

 

[DAT Destroyer]

You have phenyl ethanone and use reactants Excess D2O and DCl (catalytic). Apparently reaction occurs at the alpha position. What is this reaction?

This reaction is a substitution reaction whereby we remove the alpha hydrogens and replace them with deuteriums. In base, we form an enolate intermediate, in acid we form an enol intermediate.

Hope this helps.

Dr. Jim Romano

 

[DSNCSUN]

This reaction is a substitution reaction whereby we remove the alpha hydrogens and replace them with deuteriums. In base, we form an enolate intermediate, in acid we form an enol intermediate.

Hope this helps.

Dr. Jim Romano

Thank you for the help. One more question, why is C2H5OH a weaker Nucleophile than CH3SH. I believed that Nucleophilicity had the same trend as basicity, unless in protic solvent then size would be opposite trend and larger would win, but the question did not specify the solvent just asked which is the best Nu? a) h20 b) AlCl3 c) C2H5OH d) CH3SH e) CH3COOH

 

[Crithu]

Thank you for the help. One more question, why is C2H5OH a weaker Nucleophile than CH3SH. I believed that Nucleophilicity had the same trend as basicity, unless in protic solvent then size would be opposite trend and larger would win, but the question did not specify the solvent just asked which is the best Nu? a) h20 b) AlCl3 c) C2H5OH d) CH3SH e) CH3COOH

Nucleophilicity is the ability of the atom to give up its electrons, or act as a Lewis base. This means that atoms with a weaker hold on their electrons will be stronger nucleophiles. The trend for this goes from fluorine to francium (top right to bottom left), opposite the electronegativity trend. The trend for basicity goes toward Boron (from bottom right to top left).

So, if you have it narrowed down to C2H5OH and CH3SH, the stronger nucleophile is CH3SH. Both Oxygen and Sulfer are in the same group and the atom in the highest period (furthest down) will be the better nucleophile.

 

[tommyngu]

This reaction is a substitution reaction whereby we remove the alpha hydrogens and replace them with deuteriums. In base, we form an enolate intermediate, in acid we form an enol intermediate.

Hope this helps.

Dr. Jim Romano

Just curious. When you have excess D2O and DCl as a catalyst, does this effectively give you D3O+? So the reaction is essentially phenylethanone + D3O+?
If so, and this reaction is going to occur like an aldol or claisen condensation in acid, except that the enol takes a D from D3O+ instead of attacking another carbonyl compound, wouldn't the ketone with the 3 deuteriums in the alpha position continue to react by having a D2O attack the carbonyl carbon and eventually producing a geminal diol?

 

[DAT Destroyer]

Thank you for the help. One more question, why is C2H5OH a weaker Nucleophile than CH3SH. I believed that Nucleophilicity had the same trend as basicity, unless in protic solvent then size would be opposite trend and larger would win, but the question did not specify the solvent just asked which is the best Nu? a) h20 b) AlCl3 c) C2H5OH d) CH3SH e) CH3COOH

As a general rule, SULFUR nucleophiles beat O and N nucleophiles, There are many reasons, but I will keep this simple. The Sulfur atom is large, and not very electronegative.......we say that the electrons are quite loose and therefore the molecule is polarizeable. Having loose electrons means that we can use them for attacking purposes. As a nice rule,,,,,NEVER bet against a Sulfur nucleophile,,,,,such as CH3S-.....they are super strong regardless of solvents !!!!!! In Advanced Organic Chemistry and Quantum Mechanics we see that there is another reason. Sulfur and Phosphorus nucleophiles along with CN- have very HIGH energy orbitals.......the orbital in particular is called HOMO...and this is a key to their reactivity, and possibly a reason for why solvents dont seem to affect their reactivity very much. As a general rule.....as we go down a group nucleophilicity increases since size increases and electronegativity decreases. Hope this helps.

Dr. Romano

 

[DAT Destroyer]

Just curious. When you have excess D2O and DCl as a catalyst, does this effectively give you D3O+? So the reaction is essentially phenylethanone + D3O+?
If so, and this reaction is going to occur like an aldol or claisen condensation in acid, except that the enol takes a D from D3O+ instead of attacking another carbonyl compound, wouldn't the ketone with the 3 deuteriums in the alpha position continue to react by having a D2O attack the carbonyl carbon and eventually producing a geminal diol?

LOL.....what a perspicacious kid you are ! Indeed this can and DOES occur......but diols are not stable in general, and the reaction simply reverses !!!!

Keep up the great work !!!

Dr. Romano

 

[Minions2015]

Hey guys, i have been going through OChem destroyer today also and i realized the most common question i miss is "Which one of these are the most acidic proton?" whats the best way to approach this? what i do is pick the most electronegative atom attached to the hydrogen but it doesn't work.

 

[tommyngu]

Hey guys, i have been going through OChem destroyer today also and i realized the most common question i miss is "Which one of these are the most acidic proton?" whats the best way to approach this? what i do is pick the most electronegative atom attached to the hydrogen but it doesn't work.

Check this out: http://www.masterorganicchemistry.com/2010/09/22/five-key-factors-that-influence-acidity/

 

[DSNCSUN]

Hey guys, i have been going through OChem destroyer today also and i realized the most common question i miss is "Which one of these are the most acidic proton?" whats the best way to approach this? what i do is pick the most electronegative atom attached to the hydrogen but it doesn't work.

Here's a rule from destroyer, although it talks about different molecules maybe it is applicable to different protons of the same molecule as well:
aromatic acids > carboxy acids > alcohols > ket/ald > alkynes > alkenes > alkanes