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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: myelver10 on October 21, 2004, 06:48:42 PM

Title: E-Z isomerism
Post by: myelver10 on October 21, 2004, 06:48:42 PM

which of the following alkenes exhibit e-z isomerrism?
a) 1-chloropropene
b) 2-chloropropene
c) 3-chloropropene

i don't understand if the chlorine is a t the two spot or if its the double bond  


                                        THANKS!!!!

Title: Re:E-Z isomerism
Post by: movies on October 21, 2004, 09:40:35 PM

Quote from: myelver10 on October 21, 2004, 06:48:42 PM

i don't understand if the chlorine is a t the two spot or if its the double bond  

It'd be the chlorine at the 2 position.

Title: Re:E-Z isomerism
Post by: maxyoung on October 28, 2004, 11:04:06 AM

should be 1-chloropropene

Title: Re:E-Z isomerism
Post by: Mitch on October 28, 2004, 07:28:11 PM

I would also go for (a).

Title: Re:E-Z isomerism
Post by: Rotwang on November 01, 2004, 10:47:36 AM

Definitely the 1st one.

Title: Re:E-Z isomerism
Post by: wgmwwggmmwgm on November 06, 2004, 09:24:40 PM

the 1st.

Title: Re:E-Z isomerism
Post by: Winga on November 08, 2004, 09:15:58 AM

But it is not necessary to use E-Z to describe the 1st compound. Just using trans-cis is OK.

Title: Re:E-Z isomerism
Post by: movies on November 08, 2004, 11:37:07 AM

That's true in this case, but it is always better to use the E/Z nomenclature.  The E/Z nomenclature can't be wrong, but trans and cis can be.

Title: Re:E-Z isomerism
Post by: dexangeles on November 10, 2004, 01:43:05 AM

the numbers before chloro specify where the halo (chloro) is located at what Carbon, and the name tells you that the double bond is located on the C1=C2, unless another number came up after the chloro and before the propene, that would've told you where the double bond is located.
When it is not specified, it is understood that it is in the C1=C2 location

so, your answer is #1 (a)

if the chlorine is on the 2nd or 3rd Carbon, your C1 will be left with 2 Hydrogens, and the number one rule of E-Z is if one of the carbons in the double bond have 2 of the same substituent, you cannot have and E (opposite) or Z (same side)

and yes use E-Z, specially you have substituents connected to the C=C that are different, and not the usual carbon or hydrogen

Title: Re:E-Z isomerism
Post by: Winga on November 10, 2004, 07:40:03 AM

So, E-Z is better to use when there are 3 or more different substituents bonded to alkenes.

Title: Re:E-Z isomerism
Post by: movies on November 10, 2004, 02:20:19 PM

Yes, when there are 3 or 4 groups on the alkene you should always use the E/Z nomenclature.  It's a good idea to use it for disubstituted alkenes too though.

Title: Re:E-Z isomerism
Post by: dexangeles on November 10, 2004, 10:37:41 PM

cis or trans is used when alkyl groups are directly connected to the C=C double bond

E-Z is used when you have different substituents like Oxygen, Chlorine, Bromine
remember, unlike cis or trans, E-Z is dependent on molecular mass (which ones have higher or lower)

Title: Re:E-Z isomerism
Post by: movies on November 11, 2004, 04:07:45 PM

E/Z also applies when you just have alkyl groups though.  The groups are defined by priority, just as they are in determining R/S configurations of chiral centers.  There is a pretty good explanation here: http://www.cem.msu.edu/~reusch/VirtTxtJml/sterisom.htm

Title: Re:E-Z isomerism
Post by: dexangeles on November 11, 2004, 05:53:38 PM

i agree with you movies, i just want the poster to realize how E-Z nomenclature came about