Which Alkenes Can Exhibit Cis/Trans Isomerism?

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In summary, In summary, all of the compounds have cis/trans isomerism with respect to the substituents around the C=C. The ones with one double bond have cis isomerism with respect to the H at one end, and the ones with two double bonds have trans isomerism with respect to the H at both ends.
  • #1
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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  • #2
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?
 
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  • #3
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.
 
  • #4
Oh & btw..when there are no locants for the alkene..then we're supposed to assume it as 1.
 
  • #5
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?
 
  • #6
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.
 
  • #7
& 1,2-dibromcyclodecene also has cis/trans.I just didnt know how to draw it.
 
  • #8
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?
 
  • #9
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?
 

FAQ: Which Alkenes Can Exhibit Cis/Trans Isomerism?

1. What is cis/trans isomerism in alkenes?

Cis/trans isomerism is a type of stereoisomerism that occurs in alkenes, which are molecules with a carbon-carbon double bond. In cis/trans isomerism, the arrangement of the atoms or groups around the double bond differs, resulting in different physical and chemical properties.

2. How does cis/trans isomerism affect the properties of alkenes?

Cis/trans isomerism can significantly impact the physical and chemical properties of alkenes. For example, cis isomers tend to have higher boiling points and melting points than their trans counterparts. They may also have different reactivity and stability due to the spatial arrangement of their atoms or groups.

3. What causes cis/trans isomerism in alkenes?

The presence of a double bond in alkenes allows for rotation around the bond, resulting in different spatial arrangements of the atoms or groups attached to the double bond. This rotation can lead to the formation of cis and trans isomers, which have different arrangements of the atoms or groups on either side of the double bond.

4. How can you determine if an alkene has cis/trans isomers?

The presence of cis/trans isomers can be determined by examining the molecular formula and structure of the alkene. If the alkene has different substituents on each carbon of the double bond, it is likely to have cis/trans isomers. Additionally, techniques such as NMR spectroscopy and X-ray crystallography can be used to confirm the presence of cis/trans isomers.

5. Can cis/trans isomerism occur in other types of molecules?

Yes, cis/trans isomerism can occur in other types of molecules, such as cyclic compounds and alcohols. In these cases, the isomers have different arrangements around a ring or a single bond, rather than a double bond. This phenomenon is known as geometrical isomerism and is similar to cis/trans isomerism in alkenes.

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