Talk:Cis–trans isomerism

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 symmetrical and cancel 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}}."

--

In general - a trans isomer has more symmetry than a corresponding cis... therefore, a crystal lattice formed by trans isomers is usually more "packed" in together, Which is not possible in a cis (especially if it has bulky groups which cause repulsions) and even if a trans Does have bulky groups it still wont cause any repulsions and in fact, its dipole moment will cancel out (DM. being a vector and all...) Also - since cis is weaker packed in the lattice, the bonds are easier to break and thus- it is more soluble (as bonds broken by higher dielectric constant of polar solvents)

Therefore - cis is more soluble than trans.. but trans is denser than cis. (in general - especially where stability (trans > cis)) Neeya The Great (talk) 14:59, 31 May 2011 (UTC)

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)

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)

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)

Well, no. Cis-trans isomerism and Geometric Isomerism are synonymous but are still used separately... In fact (in India at least!) The term Geometrical Isomerism is also used... Can we mention that too?Neeya The Great (talk) 15:02, 31 May 2011 (UTC)

The move to Cis-trans isomerism was done 4 years ago, on 19 May 2007 according to the revisio history. Please leave the title alone now. Dirac66 (talk) 15:27, 31 May 2011 (UTC)

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)

Inorganic examples?

This article deals exclusively with organic chemistry. We also need a section which explains cis-trans isomers in square planar complexes (notably cisplatin) and octahedral complexes of transition metals. Dirac66 (talk) 02:17, 28 February 2009 (UTC)

Trans effect probably has plenty of relevant content.

Ben (talk) 12:28, 28 February 2009 (UTC)

The trans effect article lacks a simple explanation of what a trans isomer is, presumably because it is written at a more advanced level and assumes the reader already knows the basics of square planar complexes. I think the explanation belongs in this more elementary article; then the trans effect article can link here. Dirac66 (talk) 19:47, 28 February 2009 (UTC)

Cyclooctene isomer boiling points

The edit today by 212.159.200.163 was reverted today without comment by DMacks, but does point to a real problem. On checking the references in the article, the cis isomer boiling point is given in Ref.2 (Akros data) as 145oC at an unstated pressure - without checking further one would normally assume a normal boiling point at 1 atm. The trans isomer boiling point however is given in Ref.3 (Organic synthesis) as 75oC at a reduced pressure of 78 Torr (mm). The comparison of boiling points of two liquids at two different pressures is not meaningful without further data, (although the statement "so no difference" inserted by 212.159.200.163 is too simple). Therefore I think the comparison of these two values is invalid and should be deleted - unless someone finds that the cis isomer was also measured at or near 78 Torr. Dirac66 (talk) 19:33, 5 November 2009 (UTC)

Concur. This kind of data would be great to have, really illustrating that these are two distinct compounds if there are known and different BP (but otherwise it doesn't add anything to the discussion on the topic of cis/trans). 75°C@78mmHg calculates to be 150°C@760mmHg, so "close" but that assumes ideal gases, etc. I reverted based on the positive (and uncited) assertion that they are the same (rather than similar within the bounds of assumed/unstated experimental conditions). DMacks (talk) 19:58, 5 November 2009 (UTC)

Yes, that edit should really have been on this talk page, so let's pretend it was :-) Your calculation requires heats of vaporisation to insert in the Clausius-Clapeyron equation - I presume you used Trouton's or a similar rule? Meanwhile I have checked my old Handbook of Chemistry and Physics (60th edn 1979) and found two normal b.pts. cis 138°C (close to 145°C in article), trans 143°C (close to your 150°C). Clearly this pair of molecules is not an example of a large isomeric difference in boiling point as the article claims, so it should be deleted.

Next question - what would be a better example? Presumably more polar molecules. The next paragraph mentions maleic and fumaric acids, but their boiling points are not given in the (1979) Handbook, which often means that they decompose before boiling. However the melting points are given as maleic 139-140°C and fumaric 300-302°C. What do you think of replacing the example of cyclooctene b.pts with these two m.pts.? Dirac66 (talk) 20:38, 5 November 2009 (UTC)

I have now replaced the invalid (because measured at two different pressures) cyclooctene boiling points by the boiling points for the 1,2-dichloroethenes. Melting points have a different explanation so belong in the next paragraph, to which some numerical values can be added. Dirac66 (talk) 17:47, 12 November 2009 (UTC)

Redraw image of cisplatin and transplatin

I would like to ask that the image of cisplatin and transplatin be redrawn. It was drawn in 2011 as a vector image to update the raster image File:Cisplatin and transplatin.gif which I had drawn in 2009 (and which will soon be deleted from Wikipedia as it is no longer used in any article). The problem here is that the vector version does not conform to the usual chemistry conventions for showing the spatial geometry of the molecule, since the four ligands are in a square implying a planar diagram, but the bonds are shown as wedges and dotted lines implying a 3-dimensional diagram. So the vector image should be redrawn, but I do not have software to draw vector images, so I would like that the image be redrawn with the four ligands in a rectangle as in my diagram, and also as in the article on cisplatin. Dirac66 (talk) 20:14, 3 August 2013 (UTC)

Open-chain molecules

Last sentence of first paragraph: Cis and trans descriptors cannot be used in open-chain molecules, where syn and anti are used instead. I do not understand what this is supposed to mean, since all of our examples are in fact open-chain molecules except for the one pair of dichlorocyclohexanes. Can someone fix this sentence, or should it be deleted? Dirac66 (talk) 00:18, 8 February 2014 (UTC)

The missing detail was the difference of whether it was an alkene (or other similarly-rigid form). I think it's simply supposed to be stating the logical opposite or alternative to what is explicitly included in the earlier sentences (geometrically fixed cases, such as rings and alkenes). I adjusted the wording, with link to the aspect of variable geometry. DMacks (talk) 12:18, 8 February 2014 (UTC)

Thanks. I have added a missing not to your edit. The sentence is much clearer now. Dirac66 (talk) 00:03, 9 February 2014 (UTC)

• blush* good catch. DMacks (talk) 04:01, 9 February 2014 (UTC)

Italics Comment Fixing style/layout errors

I removed erroneous italics. While they are commonly italicized, this is a misunderstanding. "Cis" and "trans" are English words; they are only italicized as part of a chemical name. See The ACS Style Guide, 3rd ed., pp.145, 235. ~ Lhynard (talk) 21:13, 12 December 2014 (UTC)

Re-word comparison to E/Z isomerism?

I propose that the article's second sentence be made more clear. It states:

[Cis/trans isomerism] is not to be confused with E/Z isomerism, which is an absolute stereochemical description, and only to be used with alkenes.

Does this mean that Cis/trans should only be used with alkenes, or that E/Z is only to be used with alkenes?

Christopher.ursich (talk) 17:03, 23 April 2015 (UTC)

Good question. A related question is what of type of molecule is excluded, since the section E/Z notation shows that halosubstituted alkenes are in fact included. So I checked an authority: Eliel and Wilen Stereochemistry of Organic Compounds (John Wiley 1994), p.1197. Their glossary item for E, Z ends with the sentence: E and Z should not be used for substituted cycloalkanes. So I suggest the article say that E/Z notation should only be used for substituted open-chain alkenes and not for substituted cycloalkanes, possibly using Eliel and Wilen as a reference. Dirac66 (talk) 18:32, 23 April 2015 (UTC)

transification

Is there a word for the process of converting cis to trans? I thought it should be transification, but I don't see much regarding that. More specific, the way too common case of making trans fats as a side effect of hydrogenation. Gah4 (talk) 14:05, 30 October 2018 (UTC)

Isomerization is the general conversion of one isomer to another. So "cis–trans isomerization" is the interconversion between cis and trans. DMacks (talk) 15:42, 30 October 2018 (UTC)

An alternate form is "cis–to–trans isomerization". Dirac66 (talk) 17:30, 30 October 2018 (UTC)

I was trying to find a nice short word for it. It seems that transesterification is a word for that one, but not transification for this one. Thanks all. Gah4 (talk) 02:20, 31 October 2018 (UTC)

short description

It seems to me that the recent change to the short description is too short. It seems to include all isomers, which misses the whole point. Gah4 (talk) 22:05, 10 August 2021 (UTC)

Cis-trans isomers as a subtype of configurational isomers?

According to various sources I've looked at, including http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch07/ch7-1.html (which is referenced in Conformational_isomerism), configurational isomers refer to isomers where "interconversion necessarily involves breaking and reforming of chemical bonds". Thus, as I understand, configurational isomers are a subtype of stereoisomers that include both cis-trans (geometric) isomers and enantiomers, since the latter also requires the breaking of chemical bonds to interconvert. Thus, would it be right to say that cis-trans isomers are a subtype of configurational isomers (instead of implying that they are the same as configurational isomers, as mentioned at the beginning of the article)? Mosrod^Talk 12:31, 16 August 2023 (UTC)

@Mosrod: Yes, I believe you are correct. I have deleted the claim that cis-trans and configurational isomerism are the same, and added a sentence at the end of the intro to say that cis-trans is one type of configurational, using your source. Thank you. Dirac66 (talk) 17:21, 3 November 2023 (UTC)