Talk:E1cB-elimination reaction

Completion of Educational Assignment Fall 2013

We completed our final edits to this page. We expanded on the original page by describing the mechanism in more detail in addition to comparing the E1cB mechanism to the other elimination reactions. This also included a detailed discussion of the kinetics that characterize this reaction and several applications. We would appreciate any comments or recommendations that would add to this page.
Thanks!
--Paracelsus22 (talk) 15:34, 11 November 2013 (UTC)

Peer Review and Responses During Educational Assignments in Fall 2013

Comments

The start with E1cB elimination reaction is a type of elimination reaction could be improved.--Stone (talk) 21:26, 29 October 2013 (UTC)

Peer Review 1

The introduction section seems appropriate in language and length, much more so than the original page’s. It may be more helpful to place the breakdown of the name (E=elimination) first, and then proceed into the conditions. The mechanisms section could wiki-link to the inductive effect and delocalization pages to clear up the significance of those terms. The “Distinguishing from other Beta-hydride elimination reactions” section seems to be repetitive of several kinetic effects mentioned in the “Identifying E1cB-elimination mechanisms” section. It might be best if those two are merged on the final page. The Kinetic Isotope Effect in the latter section was very thorough and written in accessible language. The representative example with the Aldol reaction was well done. All in all, excellent accessible language, but make sure to link more to other wiki articles that go into some of your concepts: Steady state approximation in chemical kinetics, reversible vs. irreversible reactions, conjugate bases, nucleophiles. The original page also seems to have a good amount of technical information on specific reaction conditions and named reactions. This should be incorporated with the example reactions in the final version of the page.

The images definitely illustrate the concepts well; however there might be a minor way to improve the abbreviations for base and leaving group. It may be helpful to in the first mechanism on the page, refer to the Base as “Base (:B- )” instead of “:B” and then referring to it in the preferred convention for further mechanisms would be helpful. Novices might think you mean boron anions are good bases. Also referring to the Leaving groups as “LG” in their first image would be more acceptable notation for non-chemists. Lastly the image in the “Distinguishing from other Beta-hydride elimination reactions” may need a slight edit: in the product of k2 reaction, after the double bond forms, it should be a planar molecule. However these mechanisim and figures are much more helpful than the original article’s and they appear to be drawn accurately for the most part.

The required numbers of sources are present and well dispersed between journals and textbooks that should be available in most academic libraries.

Overall the article is very accessible to the Wikipedia audience, and is well-illustrated with pertinent and mostly accurate images. It does get repetitive in the 3rd and 4th section, and it would be best to combine these or make a separate section for only kinetics. The fact that approximately half the references are text rather than online journals is commendable as well. I think this article will definitely elucidate the concepts mentioned on the original article, which was written in much more technical language.

dgsinUM (talk)

Response

Thank you very much for your helpful insights relating to our page! We really appreciate your comments, and here are some changes that we made:

• We included many more wiki-links throughout the article. This should supplement the reader's overall experience.
• We also redid the "Distinguishing E1cB-elimination reactions from E1 and E2-elimination reactions." This section now focuses on the physical factors that influence the reaction mechanism in a broader view. To make sure these conditions were clear we also included a table. Now this sections is distinct from the kinetics section; however, there is still some overlap because kinetics to play a role in determining what type of mechanism is dominating. We just tried to make it as non-repetitive as possible while still conveying the most important information.
• We incorporated additional figures from the original page as suggested.
• We did our best to improve the overall mechanisms. This is included explicitly showing that ":B" symbolized base and "LG" stands for leaving group, and we edited our figures such that the correct 3D-structure is shown.

One change that we respectfully disagreed on relates to how we described the naming of E1cB mechanisms. You suggested that it "may be more helpful to place the breakdown of the name (E=elimination) first, and then proceed into the conditions." We felt that describing the conditions served as the first stepping stone to getting to what the name stood for. It followed the logic of "here is the mechanism and what it does, so it makes sense that it is called this."

Thank you again for your suggestions!

--Paracelsus22 (talk) 16:34, 8 November 2013 (UTC)

Peer Review 2

The introductory section is definitely an improvement over the previous page. It is not too detailed, and I think it is accessible to those who are studying sophomore level organic chemistry. However I'm not sure that in this sentence: Elimination refers to the fact that this mechanism is for a Beta-Hydride elimination that "for" is the correct word to use. Other than that I find it clear and think that less experienced chemists could understand. Also, I think the introduction should be above the table of contents. In my opinion it would make the introduction section clearer. I do think that the length of each section is helpful and the ideal length. I think the content here is helpful and necessary, and I don't think there is much duplication. Just a few notes though: saying something "will want to leave" is less scientific and might confuse readers who don't understand stability = happiness of molecules. Using "we" like in the rate law kinetic section, I think is less ideal in the wikipedia world. The kinetics discussion was relatively clear though for people who understand kinetics, but I don't think there is another way to explain it without being technical and assuming knowledge. During the isotope effect a C is missing: The use of 11C can be used. I think some more information could be used in the aldol example as it is "The most well known reaction that undergoes E1cB". I'm not sure exactly what should be added, but perhaps a description of why it is E1cb, because all that is there is a description of the mechanism (which is helpful).

Most of the figures are helpful. As a person who understands a little bit of chemistry, some of them seem a bit repetitive, but I think they could be helpful. The figure for Ethiofencarb should say that it is the molecule, otherwise it appeared to be just a seemingly overly-complicated amide/ester molecule. The figure of the beta elimination section of the E1cb is great, but the last structure should have better bond angles. I'm not sure if there are figures you could make for KIE, but if you could that would only help the section. Also, (extremely trivial) in my opinion, for consistency's sake, the font in the chemdraw figures should all be the same. Some are helvetica, and some are times new roman.

The references are good sources, mostly books and reviews, which makes them accessible. The only problem is that the in-text citations are not always consistent. Sometimes the in text citation (numbers) follow or precede the period, and they should follow the period.

I think it's a great page, especially considering where it came from, with the exception of a few small details that could be changed/expanded or clarified. A lot of aspects of the mechanism were clarified, which I think is the ultimate goal of the page. The only comments I have for improvement are the little things stated above.

Mechem13 (talk) — Preceding unsigned comment added by Mechem13 (talk • contribs) 00:00, 4 November 2013 (UTC)

Response

Thank you for your review. Here are some of the edits we made based on your comments.

1. Fixed grammar and missing text
2. Fixed informal language (we and will want to leave)
3. Added a more descriptive description of an Aldol E1cB mechansim
4. Labeled Ethiofencarb as a molecule
5. Fixed citations and figures to match
6. We kept a large quantity of figures to demonstrate the mechanism in a variety of examples, although separated the KIE and distunguishing sections which removed some repetative figures
7. We didn't add any figures for KIE because the mechanism doesn't change and if a reader is curious about how KIE works we provide a link to that Wiki page

--Physchem 13 (talk) 16:28, 8 November 2013 (UTC)

Additional Comments

UMChemProfessor (talk) 02:45, 5 November 2013 (UTC)There needs to be some consistency between each figure in terms of size, format, style, etc. For example, whether hashed/wedged bonds are used, or not. The peer reviewers also made some great suggestions.

Suggestions from ChemLibrarian (talk) 03:29, 5 November 2013 (UTC)

1. You do not need to title the first paragraph as Introduction. Just delete the heading "Introduction". People usually know the first paragraph is an overview of the concept.
2. I noticed that we you upload the images, you did not follow the instruction to upload it in Wikimedia Commons first and assign it as your own work. So, some of them are actually labeled as potential copyright violating. So, please fix the images by following instructions in this video here and re-upload your images and re-insert them in the article (video about uploading images) . Let me know if you need further help.

Additional Response

1. We fixed the formatting of our pictures to match.
2. All figures are now uploaded to the wikipedia commons
3. The "introduction" heading was removed

--Physchem 13 (talk) 16:36, 8 November 2013 (UTC)

Merge this page with elimination reactions.

This page should be merged with elimination reactions

I agree IlyaV 20:08, 9 March 2008 (UTC) —Preceding unsigned comment added by IlyaV (talk • contribs)

• Disagree, this particular reaction is not entry level material like the other elimination reactions so better leave it here .V8rik (talk) 20:31, 9 March 2008 (UTC)

Rating

I rated this page as mid, but I suspect it could be high importance if viewed in light of the Elimination reaction article. To my mind, E1cB is less fundamental than E1 and E2, but I'm flexible as to which of mid/high it falls into. Brammers (talk/c) 17:08, 8 January 2012 (UTC)

Mistakes

In my opinion, this article contains mistakes.

1. It states: "This reaction mechanism explains the formation of alkenes from (mostly) alkyl halides through a carbanion intermediate". However, alkyl halides are absolutely not typical substrates for E1cB.

2. It states: "The reaction takes place around a sp3 - sp3 carbon to carbon covalent bond with an α-acidic hydrogen atom substituent and a β-leaving group". alpha and beta to what??? Seems someone forgot to mention the presence of a mysteriously acidifying functional group?

This one is o.k., I misunderstood the original sentence.

3. It states: "This leaving group can be a halide or a sulfonic acid ester such as a tosyl group." However, E1cB is only possible if the leaving group is not overly good. For halides and sulfonates, I expect E2 mechanisms. Why should such potent leaving groups wait before they eliminate. Fluoride may be the most typical of all halides for E1cB, because it is such a bad leaving group.

4. It states: "A named reaction displaying E1cB elimination mechanism is the Boord olefin synthesis." However, the Boord olefin synthesis does not start from an acidic CH substrate, but from a halo-hetero-substrate, where the halo is reductively converted to a carbanion, which must be an irreversible step. So, the carbanion in that reaction is generated irreversibly, and in the absence of a base. That is certainly not a typical E1cB mechanism, since the acid to the conjugated base is not the starting material.

5. The most common examples for E1cB (aldol elimination) are not even mentioned, when some fancy special cases from recent research literature is treated in all detail.116.14.37.220 (talk) 12:33, 22 March 2013 (UTC)

• General literature is lacking here and you make valid points, I will make an effort to fact-check the article against some of the general text books V8rik (talk) 20:50, 23 October 2013 (UTC)

My comments:

• point 1, agreed, alkyl halides not typical substrates
• point 3, removed statement, my sources are silent on the nature of the leaving group
• point 4, true but March classifies Boord as E1Cb
• point 5, my sources do not mention Aldol so it is not up to me to have it included. There is really nothing against mentioning special cases. General references now included. V8rik (talk) 14:07, 2 November 2013 (UTC)