Talk:Cis-trans isomerism
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[edit] trans isomers and density
If trans isomers line up better than cis isomers, wouldn't their density be greater rather than lower? -- postglock 08:52, 17 September 2005 (UTC)
- I would agree; that's what I came to this page to check on. This is borne out by looking at the density values for maleic and fumaric acid. - R.
Ok, well I changed the aricle to reflect this hypothesis that R. and I share, and added a unverified header... If anyone could help that would be great. Thanks! -postglock 09:32, 31 March 2006 (UTC)
Cis have more dipoles then trans because in trans they are more symetrical and cancle out. In Trans no/less dipoles so there is less intermolecular bonds and the molecules may not be very close to each other, while in Cis, generally they have have more dippoles leading to more intermolecular bonds and they are closer together so a greater density. I'll remove the line, because it's desputed and not vital anyone disagree post here. The extra intermolecular bonds are clear by the phase change temps.Wolfmankurd 20:07, 13 June 2006 (UTC)
"Trans isomers in general also have higher [[density|densities]] {{citationneeded}}."
"Trans isomers in general also have lower [[density|densities]] {{citationneeded}}."
[edit] trends cis-trans?
I have simply looked up some boiling points for cis and trans isomers of some alkenes at: http://www.chemicalland21.com/info/Alkene%20Compound%20Boiling%20Points.htm I noticed that for 2-Pentene, 3-pentadiene, 2-Hexene, and 1,3,5-Hexatriene the cis diastereomer had a higher boiling point opposite of what is stated in wiki. I think that the content concerning general trends should be eliminated and replaced with specific and sited examples since the difference between the two isomers is very specific to the molecules in question.
trans-2-Pentene 36, cis-2-Pentene 37
1,trans-3-pentadiene 42, 1,cis-3-pentadiene 44
cis-3-Hexene 66, trans-3-Hexene 67
trans-2-Hexene 68, cis-2-Hexene 69
trans-1,3,5-Hexatriene 78, cis-1,3,5-Hexatriene 79
4-Methyl-cis-2-hexene 87, 4-Methyl-trans-2-hexene 88
-M_stone 16:02, 7 May 2006
- Makes good sense to me. DMacks 15:39, 8 May 2006 (UTC)
[edit] Form of E/Z notation
What is the correct form of E/Z notation? The article shows roman, boldface roman, italic, and parenthesised italic. Let's get this right! —The preceding unsigned comment was added by 128.250.204.118 (talk) 08:17, 20 January 2007 (UTC).
- It would seem from the IUPAC's recommendation that it should be (E)-but-2-ene -- parenthesized italic (see Enclosing marks and Italicization) IMacWin95 21:07, 21 January 2007 (UTC)
[edit] Move?
The page states relatively early on that "the term "geometric isomerism" is an obsolete synonym of "cis-trans isomerism" and its use is strongly discouraged." If the usage is discouraged, then I think that this page should be moved to cis-trans isomerism and geometric isomerism should redirect, not the other way around... IMacWin95 20:56, 21 January 2007 (UTC)
- Support, but above message is 4 months old. Dunno if I should just do the move then. Ohwell32 22:06, 14 May 2007 (UTC)
[edit] difference (cis-trans) (E-Z)
E=trans
Z=cis
right? - I couldn't find that anywhere. So I wonder if it's correct ... Or didn't I look good enough? --Saippuakauppias ⇄ 14:51, 3 January 2008 (UTC)
- It appears to be answered in the "E/Z notation" section of the article. DMacks (talk) 15:58, 3 January 2008 (UTC)
- No, the two notations (cis/trans and E/Z) are different, and only coincide in the special case of two identical substituents, who have the highest priority.
- Please review the section "E/Z notation", and consider the image there. Using the cis/trans notation that substance can be called "trans-1,2-dichlorobromoethene" (since the two chlorine atoms are on opposite sides); bromine has a higher priority than chlorine, so the two highest priority atoms there are actually bromine and chlorine (the chlorine on the top right), and so using E/Z notation this material is the Z isomer - (Z)-1-bromo-1,2-dicholroethene. okedem (talk) 16:06, 3 January 2008 (UTC)
- cis/trans naming doesn't relate to two "identical" substituents on the ends of the alkene, but rather "two substituents" at all. Cinnamic acid can rightfully be called trans. Likewise, your dichlorobromoethane example doesn't seem valid precisely because nobody knows what is cis or trans to what. DMacks (talk) 16:19, 3 January 2008 (UTC)
- Oh, right, not identical. About the "trans" - I can't really argue about it. I seem to recall seeing such use of the cis/trans notation, but it's been a while since I actually dealt with this side of chemistry. So, essentially, we can say that for the case of 2 substituents we can say Z=cis and E=trans, but for anything more, we have to use the E/Z notation, since cis/trans breaks down. okedem (talk) 16:28, 3 January 2008 (UTC)
- cis/trans naming doesn't relate to two "identical" substituents on the ends of the alkene, but rather "two substituents" at all. Cinnamic acid can rightfully be called trans. Likewise, your dichlorobromoethane example doesn't seem valid precisely because nobody knows what is cis or trans to what. DMacks (talk) 16:19, 3 January 2008 (UTC)
