Carbo-cations may be stabilized by: (a) π-bonds only at allylic position (b) π-bonds only at vinylic position (c) π-bonds at allylic and benzylic position also (d) -I effect While the answer is obviously not (d), I am really confused about what 'allylic', 'vinylic' and 'benzylic' positions actually mean.

2023年9月24日 · So, the carbons in vinyl group is "vinylic" carbon and the carbon in the extra methylene bridge is the "allylic" carbon. (Picture source) Regarding the origin of the word, the respective Wikipedia page has a good information. In short: allyl comes from the scientific name for garlic, Allium sativum. In 1844, Theodor Wertheim isolated an allyl ...

The larger the electron affinity, the more tightly the electron was held. Stable carbanions hold their electron more tightly than less stable carbanions. The electron affinity of the allyl anion was measured as 0.481 eV. For the vinylic carbanion, the EA was measured as 0.667 eV.

The Link notes that "the allylic radical is stabilized by 12 kcal/mol relative to the nonallylic radical" and that "benzylic radicals are about 10 kcal/mol more stable than comparably substituted nonbenzylic radicals".

2018年3月13日 · For a positive center to be attached to a more electronegative group is destabilizing. Hence the vinylic cation is less stable than a typical alkyl cation. Things are even worse with the aryl carbocation on the right. Here the positive carbon is attached to 2 $\ce{sp^2}$ carbons. Destabilizing the aryl cation even further is its geometry.

2015年4月4日 · Why do Allylic Halides prefer SN2 reaction over Sn1? is not true. There are many cases where allylic halides react preferentially by an $\mathrm{S_{N}1}$ process. Since both the allylic $\mathrm{S_{N}1}$ and $\mathrm{S_{N}2}$ reactions are stabilized, there is a delicate balance between the two pathways. We can shift from one mechanism to the ...

2018年4月30日 · Therefore, what looks like an allylic carbocation is actually a twisted allylic carbocation. The $\mathrm{2p}$ orbitals of the double bond can't stabilize the new cation by resonance. Worse yet, the $\mathrm{2p^2}$ carbons of the double bond are relatively electronegative, so they actually destabilize the new carbocation. In other words, the ...

2022年8月8日 · $\begingroup$ If you look at "peak data" here for methacryloyl chloride ($\ce{C4H5ClO}$), you will see that there is small coupling between the two vinylic hydrogens but also weak allylic coupling to the methyl group. $\endgroup$ –

2018年8月14日 · Since 3 is vinylic hydrogen, therefore it is least acidic. Both 1 and 2 are allylic and are at the alpha position with respect to the carbonyl group. Nitrogen is quite electronegative, therefore hydrogen 1 is more acidic than hydrogen 2. Hence the result.

2017年3月1日 · You also need to consider that in a chemical reaction, stability does not only depend on the energy, but also on the reaction speed. Since primary allylic cation is sterically unhindered, it may react faster, making it less stable. Again, it is only a first guess, I do not have numbers for this. $\endgroup$ –