Quick O-Chem question on terminology

[Lacipart]

Cis & TransI get:

Trans.....................................CIS

But then there is Syn & Anti, and Threo & Erythro??

Arn't they all describing the same thing!?

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[vicinihil]

Ah

Syn and Anti describes the method of addition. Some reactants can add in the SYN fashion meaning they add to the same side of a molecule while others add in an ANTI fashion.

Threo and Erythro is used to describe carbohydrates.

 

[RoadRunner17]

No, they aren't the same thing... if you are talking about cis/trans as in isomerism, I would suggest you go back and review your Organic Chemistry textbook. Those refer primarily to alkenes (the double bonds)

Syn and anti is stereochemistry; and I'm not sure what you mean by threo and erythro, but Googling it tells me that you're talking about absolute configurations.. I would use the R/S terminology as the threo/erythro terminology is outdated.

Yeah, I would suggest you go back and review Orgo. Try Organic Chemistry as a Second Language by David R. Klein. Great book for learning the basics behind Organic Chemistry.

 

[chad5871]

I believe that syn/anti only refer to addition or elimination reactions and threo/erythro can differentiate between diastereomers but is an outdated method.

 

[jochi1543]

Granted, I've only taken Orgo I at this point, but I have never heard of the treo/erythro stuff - even after having prepared for the MCAT orgo.

The above poster is right, syn/anti is for elimination reactions. You will consider it when you are performing an elimination reaction on a molecule like a cyclohexane. Anti means that the 2 atoms you want to eliminate from the molecule are located at 180 degrees with each other, and it's required for E2 reactions - they won't proceed in a molecule with a syn conformation. Say, if you have a cyclohexane and want to remove H from C1 and Cl from C2, you want those 2 to be axial and trans in order to give an anti conformation. If they are equatorial, E2 won't happen.

 

[Lacipart]

Cool, alright, thanks guys 🙂

 

[koopa_troopa]

I don't think you cis/trans example in the post is right. I believe cis/trans/E/Z only applies to double bonds and ring structures. For saturated molecules, I think you use R/S.

As posters have stated, syn/anti used to describe how things are added/eliminated in a reaction.

An example of syn is the addition of H2 to a double bond in the presence of a metal catalyst (Pd/Pt?).

Anti addition can be seen in the addition of a halogen (Br2) to a double bond.