trans vs. cis e/z

[arginine1]

There was this question about a dipole moment on the achiever, test 2.

I got the answer right, but I wonder about their explanation:

Correct Answer: A
Ethyl, CH3CH2, is electron donating (inductive), whereas chlorine, Cl, withdraws electrons from the double bond. These collectively reinforce each other in making trans-1,2-dichlorobutene exhibit highest magnitude of dipole moment, illustrated as follows: (illustration attached in bmp. format)


so my question is, why do they call this "trans" isn't it Z? (or cis?)

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[Philippines03j]

It is Trans or E because the two groups of priority are opposite to eachother. Remember E means Eppisite (oppisite)

Cis or Z means that they would be on the same side. Remember Z means Zame (Same).

http://en.wikipedia.org/wiki/File:Cis-2-butene.svg


Cis-2-butene


(Z)



Trans-2-butene

(E)


I am not sure if that wil make sense at all but hope it helps!

 

[arginine1]

.... but how is it trans since there are 2 chlorines, both on the same side, wouldn't each one of them get a higher priority and be "cis" as a result ?

 

[Extirpator]

you're right, the two chlorine take priority, thus it's cis. Their explanation just lists the wrong nomenclature.

 

[BiomajorPreDent]

It is Z, not Cis

Z and Cis both refer to them being on the same side and
E and Trans both refer to them being on opp sides

BUT

you use Cis and Trans and E and Z for different molecules

OP: The example you showed you would use Z or E instead of Cis or Trans because there is more than 2 groups that arent H's

It has to do with subsituted groups, I am not sure how to word it im sorry.

But the example philippines03j showed would be referred to using either Cis or Trans notations

This is from wiki, you should read it as the explanation is more clear

"The cis/trans system for naming isomers is not effective when there are more than two different substituents on a double bond. The E/Z notation should then be used."

Read this whole article:

http://en.wikipedia.org/wiki/Cis-trans_isomerism

 

[dentrilla]

It is Z, not Cis

Z and Cis both refer to them being on the same side and
E and Trans both refer to them being on opp sides

BUT

you use Cis and Trans and E and Z for different molecules

OP: The example you showed you would use Z or E instead of Cis or Trans because there is more than 2 groups that arent H's

It has to do with subsituted groups, I am not sure how to word it im sorry.

But the example philippines03j showed would be referred to using either Cis or Trans notations

This is from wiki, you should read it as the explanation is more clear

"The cis/trans system for naming isomers is not effective when there are more than two different substituents on a double bond. The E/Z notation should then be used."

Read this whole article:

http://en.wikipedia.org/wiki/Cis-trans_isomerism

can anyone clarify this? Wiki isnt the greatest source.. i always thought we could use E/Z and trans/cis interchangeably

 

[Extirpator]

It is Z, not Cis

ummm... false. It's z OR cis. It has 2 chlorines (the same substituent) attached to opposite sides of the double bond, thus it's more properly refered to as cis. Although, either method of nomenclature is correct in this case.

can anyone clarify this? Wiki isnt the greatest source.. i always thought we could use E/Z and trans/cis interchangeably

Cis and trans only apply to nomenclature if you have two of the same substituents on either side of the double bond. E/Z is used when you instead need to use priorities.

E/Z can apply to all scenerios, while cis/trans requires identical substituents. Although you usually won't see E/Z naming of something that can be labeled as cis/trans.

 

[BiomajorPreDent]

thank you for clearing that up, I half assed that post I know..I was in a hurry.