Which Alkenes Can Exhibit Cis/Trans Isomerism?

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Discussion Overview

The discussion revolves around the identification of alkenes that can exhibit cis/trans isomerism. Participants are analyzing various compounds and their structural characteristics to determine which can form these isomers, with a focus on drawing and visualizing the structures involved.

Discussion Character

  • Homework-related
  • Exploratory
  • Technical explanation

Main Points Raised

  • One participant lists several alkenes and claims that only 1-chloropropene, 1,3,5-hexatriene, and 3-hexene can exhibit cis/trans isomerism.
  • Another participant questions the naming of some compounds and suggests that additional isomers may exist, prompting a request for drawings of each compound.
  • There is a discussion about the assumption of locants for alkenes when not specified, which affects the identification of isomerism.
  • One participant mentions that some compounds may exhibit Z/E isomerism instead of cis/trans due to the nature of their substituents around the double bond.
  • Participants discuss the structure of 1,2-dibromocyclodecene and express difficulty in visualizing its cis/trans forms.
  • Another participant identifies 2-pentene as an alkene that can exhibit cis/trans isomerism, indicating a reevaluation of their previous answers.
  • There is clarification that both (E) and (Z) forms of cyclodecene exist, with a focus on the structural differences between them.

Areas of Agreement / Disagreement

Participants do not reach a consensus on which alkenes can exhibit cis/trans isomerism, as there are multiple viewpoints and some uncertainty regarding the structural representations of the compounds discussed.

Contextual Notes

Participants express uncertainty about the correct representation of certain compounds and the implications of naming conventions on isomerism. There are unresolved questions about the visual representation of cis/trans forms for some alkenes.

Who May Find This Useful

Students studying organic chemistry, particularly those focusing on stereochemistry and isomerism in alkenes.

ChemDoodle
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Hey,i just need someone to check my answers :)

Which of these can exist as cis/trans isomers?
a.1-pentene
b.2-pentene
c.1-chloropropene
d.3-chloropropene
e.1,3,5-hexatriene
f.1,2-dibromocyclodecene
g.propene
h.3-hexene
i.2-hexene
j.2-methyl-2-butene

I solved it & my answers are c,e and h.Is this correct?
& about 1,2-diboromocyclodecene..I wasn't able to draw a cis/trans structure.Can someone please illustrate?

Thnakyou :)
 
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ChemDoodle said:
Hey,i just need someone to check my answers :)

Which of these can exist as cis/trans isomers?
a.1-pentene
b.2-pentene
c.1-chloropropene
d.3-chloropropene
e.1,3,5-hexatriene
f.1,2-dibromocyclodecene
g.propene
h.3-hexene
i.2-hexene
j.2-methyl-2-butene

I solved it & my answers are c,e and h.Is this correct?

c, d and f seem to have ambiguous names to me. Whilst you have locants for what I assume is the halogen in each case, you don't for the alkene. e and h certainly exist as cis / trans pairs, but you're still missing some. Can you draw each of them out?
 
Last edited:
These are the names given in my textbook & we're supposed to solve accordingly.I drew each one of them..But some of them seemed to have Z/E isomerism since none of the substituants around the C=C are similar.
 
Oh & btw..when there are no locants for the alkene..then we're supposed to assume it as 1.
 
Thanks for clarifying the locant situation - in that case all the ones you have so far are correct.

OK, let's take for instance (i). What do you have at each end of your double bond here?
 
On the first C there is H & CH3 & on the second C there is H & CH2CH2CH3.
So there is cis/trans isomerism with respect to H.Oh yes! I missed that one.Can u please point out the rest that I've got wrong? & ill draw them out.You'll save me a lot of time.Cuz we also have to draw each isomer.
 
& 1,2-dibromcyclodecene also has cis/trans.I just didnt know how to draw it.
 
ChemDoodle said:
On the first C there is H & CH3 & on the second C there is H & CH2CH2CH3.
So there is cis/trans isomerism with respect to H.Oh yes! I missed that one.Can u please point out the rest that I've got wrong? & ill draw them out.You'll save me a lot of time.Cuz we also have to draw each isomer.

That won't really help, but can you see another compound that has the name 2-(something)ene, perhaps?


ChemDoodle said:
& 1,2-dibromcyclodecene also has cis/trans.I just didnt know how to draw it.

What does the name cyclodecene imply to you?
 
Ok,so i checked each and every one again & the one that i missed is 2-pentene.Is there any other one i missed?
Cyclodecene is a cycle of 10 C & with one double bond.But i just couldn't draw the cis/trans representation..I was thinking maybe the trans rep. should be two cycles instead of the one 10C cycle?
 
  • #10
ChemDoodle said:
Ok,so i checked each and every one again & the one that i missed is 2-pentene.Is there any other one i missed?
Cyclodecene is a cycle of 10 C & with one double bond.But i just couldn't draw the cis/trans representation..I was thinking maybe the trans rep. should be two cycles instead of the one 10C cycle?

No, that's your lot. Both (E) and (Z) cyclodecenes are one ring, except in one the olefin is cis and the other, trans; just like you've been doing for all the other compounds. How are you drawing your 10-membered ring?
 

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