Orgo: NaOC2H5

[joonkimdds]

All the reactants that use NaOC2H5 from my orgo2 class had carbonyl group. What happens is that NaOC2H5 takes H from alpha carbon and that's how it initiates many different reactions such as Claisen condensation, Dieckmann condensation, Alkylation, Malonic ester synthesis....etc.

But according to DAT destroyer road map 2, it has two reactions that use NaOC2H5 but doesn't have carbonyl group, and because DAT destroyer lacks explanation, I can't even understand how these reactions proceed and their names.

Plz help me

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[sunshine222]

Those aren't really "named" reactions, they're just showing you how, under different reaction conditions, the same substrates will undergo substitution or elimination.

In the first, you have a primary alkyl halide in an aprotic solvent; the alkyl halide undergoes substitution to form the ether.

In the second reaction, the alkyl halide is secondary and you also have dissociated (Na+)(OC2H5-) in solution. (OC2H5-) is a decent base, which can abstract a proton. The combination of those two factors will result in an elimination reaction, probably an E1.

I'd definitely recommend reviewing the basics of SN1, SN2, E1 and E2 reactions - and their mechanisms - before the DAT

 

[joonkimdds]

Ah~! That's what it was.
By the way, why is C2H5OH present in the 2nd reaction? Is it really necessary to have it?

 

[sunshine222]

Well it's basically just acting as a solvent.. using ethanol ensures that there'll be plenty of dissociated ethoxide to react with the substrate. You could use any polar protic solvent, but it might compete with ethoxide and give you a mixed product.

 

[chessxwizard]

The ethanol also stabilizes the E1 cationic transition state, while in the SN2 reaction the DMSO solvates the cations pretty well, leaving the anion (ethoxide ion) to react with the halide.

 

[joonkimdds]

One more question

As soon as I see the reactants, is there a easy way to recognize that this has to be either elimination or substitution reaction but not the other reactions?

 

[keliao]

One more question

As soon as I see the reactants, is there a easy way to recognize that this has to be either elimination or substitution reaction but not the other reactions?

they are based on looking at the reactant and reactions given.
the OTHERS, do you mean by claisen condensation, aldol condensation, malonic ester, and michael ??
well..you can easily identify whether it is one of the "OTHERS" and the simple SN1/2, E1/2.
the OTHERS got like complicated structures like ketones, double bonds, carbonyl..

 

[sunshine222]

There's no surefire way, but look for distinctive reaction conditions - for example an aromatic + AlCl3 will usually be a friedel-crafts. That sort of thing.

 

[joonkimdds]

There's no surefire way, but look for distinctive reaction conditions - for example an aromatic + AlCl3 will usually be a friedel-crafts. That sort of thing.

Aromatic+AlCl3 = gives me an idea that it has to be friedel-crafts.
because it can't be anything else.

But there are so many ways that elimination/substitution can occur so as soon as I see the reactants, I don't know if it's a reaction that I just couldn't remember or if it is E/S reaction.

 

[yakuza]

Incase anyone didn't mention it, the 1st rxn looks like Williamson....1' Halide + SN2 + base

 

[klutzy1987]

The second reaction is going to be an E2 not E1. The first one is your basic SN2.

 

[sunshine222]

The second reaction is going to be an E2 not E1. The first one is your basic SN2.

Mmm... I disagree on that. It's a polar protic solvent and a secondary alkyl halide (favors e1) and you don't have a strong base that would favor E2. Why are you thinking E2?

 

[y0ssarian]

Mmm... I disagree on that. It's a polar protic solvent and a secondary alkyl halide (favors e1) and you don't have a strong base that would favor E2. Why are you thinking E2?

You don't consider ethoxide a strong enough base for the mechanism to go through E2? What are you comparing the secondary alkyl to when you say it favors E1?

 

[polarmolar]

#1 is a classic SN2, while #2 (due to the strong base) is a E2.

 

[klutzy1987]

Mmm... I disagree on that. It's a polar protic solvent and a secondary alkyl halide (favors e1) and you don't have a strong base that would favor E2. Why are you thinking E2?

NaOCH2CH3 is one of the 5 strong bases that will make an E2. The others are methoxide, Terbutoxide, and crap i forgot the others.

LOL lucky i already took my DAT and dont have to worry about it.

 

[doc3232]

Mmm... I disagree on that. It's a polar protic solvent and a secondary alkyl halide (favors e1) and you don't have a strong base that would favor E2. Why are you thinking E2?

You got a 26 on OC section but you don't consider ethoxide a strong base?
Now that I look at it again, you might have only read the bottom reagent.

NaOCH2CH3 is one of the 5 strong bases that will make an E2. The others are methoxide, Terbutoxide, and crap i forgot the others.

LOL lucky i already took my DAT and dont have to worry about it.

Those are just the common strong bases experimentally, there are no specific 5 strong bases. Put an oxide at the end of any alcohol and there you go...a strong base.

 

[joonkimdds]

Incase anyone didn't mention it, the 1st rxn looks like Williamson....1' Halide + SN2 + base

Ah!!! that makes it easier to understand