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Author Topic: Why is this cis-2-hexene?  (Read 7679 times)

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Agent-X

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Why is this cis-2-hexene?
« on: August 02, 2009, 12:50:50 PM »

Is it because the hydrogens are on the same side?

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azmanam

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Re: Why is this cis-2-hexene?
« Reply #1 on: August 02, 2009, 12:52:35 PM »

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Agent-X

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Re: Why is this cis-2-hexene?
« Reply #2 on: August 02, 2009, 02:59:42 PM »

So, the Z configuration is "cis," and the E configuration is "trans"?
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thfmag

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Re: Why is this cis-2-hexene?
« Reply #3 on: August 02, 2009, 07:55:55 PM »

That is correct; the Z/ E nomenclature comes from german. Z for "zusammen" meaning together and E "entgegen" for opposite.
So Z = cis and E = trans.

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AWK

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Re: Why is this cis-2-hexene?
« Reply #4 on: August 02, 2009, 11:09:37 PM »

That is correct; the Z/ E nomenclature comes from german. Z for "zusammen" meaning together and E "entgegen" for opposite.
So Z = cis and E = trans.


Not exactly, though in this case it works.
cis-trans concerns a carbon skeleton
Z-E concerns the highest priorities of substituents.
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Agent-X

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Re: Why is this cis-2-hexene?
« Reply #5 on: August 02, 2009, 11:16:19 PM »

Is it because the carbon-based substituents are of higher priority than the hydrogens on cis-2-hexene that makes it considered "cis"? Based on the higher priority concept, would this molecule be called Z-2-hexene?

I don't quite understand why it is called "cis" unless I take the atomic number priority into consideration.

I understand naming something by Z and E based on the first point of difference and higher priority. But when it comes to considering this cis, I can't say that the substituents and the "cis" ends are equal. They are different, but I know they are much, much different than the distanced hydrogens on opposite sides.
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azmanam

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Re: Why is this cis-2-hexene?
« Reply #6 on: August 02, 2009, 11:56:05 PM »

you have to number the substituents on one side of the double bond independent of the substitutents on the other side.  that is, you'll number priority 1 for the methyl group and priority 2 for the hydrogen on the left side of the double bond... then you'll do it again for the methyl group (#1) and hydrogen (#2) on the right side.  then you compare both #1 priority substituents.  if they're on the same side, it's Z.  if they're on opposite side, they're E.

For disubstituted olefins, it's ok to say that if they're on the same size, it's cis.  and if they're on the opposite side, they're trans.  cis/trans are really most appropriate for disubstituted olefins.  you should change to E/Z for tri and tetrasubstituted olefins.
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Agent-X

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Re: Why is this cis-2-hexene?
« Reply #7 on: August 03, 2009, 12:03:03 AM »

you have to number the substituents on one side of the double bond independent of the substitutents on the other side.  that is, you'll number priority 1 for the methyl group and priority 2 for the hydrogen on the left side of the double bond... then you'll do it again for the methyl group (#1) and hydrogen (#2) on the right side.  then you compare both #1 priority substituents.  if they're on the same side, it's Z.  if they're on opposite side, they're E.

For disubstituted olefins, it's ok to say that if they're on the same size, it's cis.  and if they're on the opposite side, they're trans.  cis/trans are really most appropriate for disubstituted olefins.  you should change to E/Z for tri and tetrasubstituted olefins.

10-4.
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