Timeline for Regioselectivity of bromination of alkenes
Current License: CC BY-SA 4.0
8 events
| when toggle format | what | by | license | comment | |
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| Aug 21, 2018 at 9:46 | comment | added | Martin - マーチン♦ | @Tan I am certain there is hyperconjugation, as there already was hyperconjugation in a substituted alkene. There probably is always something to which we refer to as hyperconjugation. You are thinking in localised orbitals, which is only one viewpoint. I can't promise that I'll be able to add any more information, I am also unsure whether I will have the time. | |
| Aug 21, 2018 at 9:30 | comment | added | Tan Yong Boon | Are you certain that there will be hyperconjugation? The geometry of bromonium is slightly different from that of the conventional carbocation. Maybe the orbitals (i.e. C-Br sigma * and C-C sigma) may not have the right symmetry/orientation? Could you illustrate more quantitatively the hyperconjugation that is taking place? I am very curious... | |
| Aug 21, 2018 at 9:00 | comment | added | Martin - マーチン♦ | @Tan No they should not. You might be confusing formal charges with partial charges. There is a significant difference in electronegativities for carbon and hydrogen, most of the electron density of the hydrogen is polarised to the carbon. Even such an over-simplified model like oxidation numbers would predict this trend. The values are certainly within expectation. | |
| Aug 21, 2018 at 8:56 | comment | added | Martin - マーチン♦ | @Tan The molecular structure is always by a delicate balance of electronic effects and orbital interactions. The molecule will adopt the structure, which is lowest in energy (or all structures accessible at a certain temperature). I am not a big fan of calling things +/-I or +/-M effects, as that are zeroth order approximations. We know that there will always be hyperconjugation from a methyl group, which will certainly the case here, too. And that much should be clear, that a positive charge will be stabilised by it. It follows basically the same trend as carbocations. | |
| Aug 20, 2018 at 23:13 | comment | added | Tan Yong Boon | Why does the calculation show that the carbons are bearing negative charges? Shouldn't they bear a partial positive charge? | |
| Aug 20, 2018 at 23:08 | comment | added | Tan Yong Boon | What could have caused the C-Br bond to the more substituted carbon to be longer? Orbital interactions? Electronic effects? | |
| Aug 20, 2018 at 23:04 | vote | accept | Tan Yong Boon | ||
| Aug 20, 2018 at 17:26 | history | answered | Martin - マーチン♦ | CC BY-SA 4.0 |