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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: kapital on February 25, 2018, 05:27:15 AM

Title: Nucleophilic substitution types
Post by: kapital on February 25, 2018, 05:27:15 AM

Would this reaction be SN1 or S12 type? Thanx for answer.

Title: Re: Nucleophilic substitution types
Post by: chenbeier on February 25, 2018, 09:42:27 AM

I think, if you mix it how it is nothing will happen. If you add NaOH to the Phenole compound before then I think it is SN2

Title: Re: Nucleophilic substitution types
Post by: kapital on February 25, 2018, 10:21:28 AM

Yes I think with addition of base. Why SN2?

Title: Re: Nucleophilic substitution types
Post by: OrganicDan96 on February 25, 2018, 12:56:54 PM

what do you know about SN1 reactions vs SN2 reactions, what are the substrate requirements.

can you describe the mechanism of these reactions?

Title: Re: Nucleophilic substitution types
Post by: Babcock_Hall on February 25, 2018, 01:03:23 PM

@OP,

It is a forum rule (see red link) that you show us your attempt or give us your thoughts, before we can help you.

Title: Re: Nucleophilic substitution types
Post by: kapital on February 25, 2018, 05:00:35 PM

SN1 does not occur with primary electrophiles, unless stabilisating group is presented, so if reaction doess happen it is SN2?

Title: Re: Nucleophilic substitution types
Post by: OrganicDan96 on February 25, 2018, 05:45:58 PM

Quote from: kapital on February 25, 2018, 05:00:35 PM

SN1 does not occur with primary electrophiles, unless stabilisating group is presented, so if reaction doess happen it is SN2?

yes but do you know why?

Title: Re: Nucleophilic substitution types
Post by: kapital on February 25, 2018, 06:42:00 PM

Carbocation is not enough stable, so it does not form?

Title: Re: Nucleophilic substitution types
Post by: kapital on February 26, 2018, 12:13:47 PM

What aboaut intramolecular hydrogen bonding?(alchohol and ester) Would it have effect on reaction?

Title: Re: Nucleophilic substitution types
Post by: Babcock_Hall on February 26, 2018, 12:37:34 PM

I don't have direct experience with this situation, but I would give some thought to the inertness or lability of the other functional group in your aromatic compound, and how its reactivity might affect one's choice of base, as a practical matter.  This issue is tangential to the question of mechanism of the substitution, however.

Title: Re: Nucleophilic substitution types
Post by: kapital on February 26, 2018, 01:45:17 PM

Yes I know, I am interested in theoretical and practical aspects of the reaction. Why would be the choice of base important? Shouldnt anything of NaOH or stronger be enoug to take proton away?

Title: Re: Nucleophilic substitution types
Post by: Babcock_Hall on February 26, 2018, 01:54:24 PM

If you use NaOH, I would worry about a side reaction involving the ester (can you identify it?).  Also phenolic protons are more acidic than aliphatic alcohols (for example, ethanol), which can be seen by comparing their pK_a values.  Therefore, I would consider both thermodynamic (how strong it is) and kinetic (how reactive it is) properties of the base.

Title: Re: Nucleophilic substitution types
Post by: OrganicDan96 on February 26, 2018, 04:37:02 PM

potassium carbonate works quite well as a base for these type of reactions

Title: Re: Nucleophilic substitution types
Post by: wildfyr on February 26, 2018, 06:42:35 PM

NaOH would cause elimination of the chloride faster than SN2 of the phenol. And potassium carbonate is the classic base for this reaction, typically referred to the Williamson ether synthesis.

Title: Re: Nucleophilic substitution types
Post by: Babcock_Hall on February 26, 2018, 08:33:04 PM

@OP,
Why don't you compare the pK_a values for the conjugate acids of carbonate and hydroxide with each other and with the pK_a of the phenol?

The possible side reaction I mentioned is base-promoted hydrolysis of the carboxylic ester.