Timeline for Torquoselectivity: Disrotatory ring opening
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8 events
| when toggle format | what | by | license | comment | |
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| Jun 13, 2015 at 18:21 | vote | accept | laminin | ||
| Jun 13, 2015 at 18:11 | comment | added | ron | Yes, at least we could make a good guess. There are 2 possible disrotatory motions. The one that would place the "E" down, has the "E" group and the tertiary hydrogen at the ring juncture approaching each other (sterically preferred). Disrotation to place the "E" up, has the E group and the other rings approaching each other (sterically less preferred). | |
| Jun 13, 2015 at 17:58 | comment | added | laminin | I really like your question, but I'm not completely happy with my chemical understanding of this reaction. Can we predict from stereoelectronic arguments (by assuming E=COOH) why in the initial question the thermally allowed disotatory ring closure gives this preferedly the above mentioned product (Me and H pointing towards us) and not the one in which the methyl group and hydrogen atom of the newly formed bond are pointing at the back? | |
| May 8, 2015 at 23:25 | history | edited | ron | CC BY-SA 3.0 |
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| May 8, 2015 at 22:57 | comment | added | ron | "I guess a möbius overlap resulting in the two methyl groups in anti relationship is sterically disfavored, isn't it?" Mobius type overlap occurs during conrotatory motion, when the top of one p orbital overlaps with the bottom of the other p orbital to which it is forming a bond. Conrotatory (Mobius) motion is allowed thermally in 4 pi systems. Disrotatory motion is allowed thermally in 4n+2 pi systems. It is orbital symmetry (not steric factors) that prevent formation the methyls in the anti arrangement in the present 6 pi electron example. | |
| May 8, 2015 at 22:49 | comment | added | laminin | In order to deal with the specific question I've updated my post. Your answer helped me a lot to remind the basic concepts. For small cycles we mostly consider only Hückel overlap (the methyl groups are syn): I guess a möbius overlap resulting in the two methyl groups in anti relationship is sterically disfavored, isn't it? | |
| May 8, 2015 at 22:02 | history | edited | ron | CC BY-SA 3.0 |
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| May 8, 2015 at 21:43 | history | answered | ron | CC BY-SA 3.0 |