How to tell between Electron Donating or Electron Withdrawing? : Mcat
Despite their high bond dissociation energy, cobaltocenium mechanophores are found to be selective sites of main chain scission under sonomechanical activation. Computational CoGEF calculations suggest that the presence of a counterion to cobaltocenium plays a vital role by promoting a peeling mechanism of dissociation in conjunction with the initial slipping. All electron-donating groups are activating groups and all are ortho-para directors with the exception of substituents, all electron-withdrawing groups are deactivating groups and all are meta directors. Hydrogen abstraction from the methyl group of methylbenzene produces a radical called the radical.
- I won’t mind adding "political science" to the list.
- The allyl cation and allyl anion are just two examples to illustrate the above concept.
- Because thiolate ions are also excellent nucleophiles, thioethers can react again to give a thioether.
- The group which directs the second incoming group to the meta position, is called a meta-director.
- This entire subject is a bit complicated, but I believe I have a good explanation for the data Pauling was attempting to explain.
From these examples, we can see that the electronic effects of the allylic double bond is highly dependent on the system we are considering. We can also seem to qualitatively derive the rule of thumb that the allylic double bond donates or withdraws based on the "needs" of the adjacent site. If it is electron-deficient, there would be donation from the double bond. If there is a site of high electron density, there would be withdrawal towards the double bond. Attack occurs at the ortho and para positions, which have formal negative charges that indicate π electron excess at these positions.
If the electronegative atom is then joined to a chain of atoms, usually carbon, the positive charge is relayed to the other atoms in the chain. You have discovered the ‘electronegativity paradox’ (also known as why Pauling’s electronegativity scale is wrong). Another scale of electronic effects is the Hammett scale for aromatic substituent effects. Although this does not measure electron withdrawing properties, it can reveal an ability to withdraw or donate charge. If you look at it, you will find that a methyl group is electron donating compared to hydrogen. In that case, you should expect hydrogen to be more electron withdrawing.
One of these lone pairs can be donated to a bond with the hydroxyl group carbon. This pushes the electrons from the carbon-carbon double bond to the carbon that it ortho to the hydroxyl group carbon. This resonance structure has a formal plus charge on the oxygen, and a formal minus charge on the ortho carbons.
Nomenclature rules allow us to name alkyl halides and alcohols. In an elimination reaction, a double bond is formed as an HX or an HOH molecule is removed. The effect is illustrated for electrophilic aromatic substitutions with alkyl substituents of differing steric demand for electrophilic aromatic nitration.
Using what you determined in question 4, label each compound below as electron donating or…
Question about bases and electron donating/withdrawing groups… In fact, I’ve seen some sources say that ester OR groups are actually electron donating , which is contrary to what Uworld says. Absence of Stereodirecting Participation by 2-O-Alkoxycarbonylmethyl Ethers in 4,6-O-Benzylidene-Directed Mannosylation. Typically NaH is used as a suspension in THF, a solvent that resists attack by strong bases but can solvate many reactive sodium compounds. Thioethers are prepared by the SN2 reaction between an alkyl halide and a thiolate ion.
At the same time, Oxygen is highly electronegative, so I’d expect it to have some withdrawing capacity. The following table shows the effect substituents have on both the rate and orientation of electrophilic aromatic substitution reactions. Phenol is an ortho/para director, but in a presence of base, the reaction is more rapid. It is due to the higher reactivity of phenolate anion.
Confusion on electron withdrawing and donating effects of alkoxy, amide, ester groups
Symmetrical thioethers can be prepared by treating the alkyl halide with KOH and hydrogen sulfide where the latter is not in excess. The nitro group can withdraw electron density through resonance. When both group have similar directing effect and are para to each other, the third substituent depends on the less hindered one.
The inductive and resonance properties compete with each other but the resonance effect dominates for purposes of directing the sites of reactivity. For nitration, for example, fluorine directs strongly to the para position because the ortho position is inductively deactivated (86% para, 13% ortho, 0.6% meta). On the other hand, iodine directs to ortho and para positions comparably (54% para and 45% ortho, 1.3% meta). Some common ortho para directing groups are –Cl, -Br, -I, -OH, -NH2, -CH3, -C2H5. The group which directs the second incoming group to the meta position, is called a meta-director. For example, alkylation of nitro benzene gives m-alkylnitro benzene as major product.
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Substitution reaction can follow S N 1 or S N 2 mechanisms. Both mechanisms follow different conditions and offer different products. Alkyl halides also form important Grignard reagent which is commonly utilized to make carbon – carbon bonds.
Connect and share knowledge within a single location that is structured and easy to search. Chemistry Stack Exchange is a question and answer site for scientists, academics, teachers, and students in the field of chemistry. When both group are the same director, the third substituent depends on the stronger one.