Share This Video. Apne doubts clear karein ab Whatsapp par bhi. Try it now. Ab clear karein apne doubts Whatsapp par bhi. Apna phone number register karein. Ab aap Whatsapp pe solutions paa saktey h, hum aapko message karenge. But the delocalisation spreads this charge over the whole of the COO group.
Because oxygen is more electronegative than carbon, you can think of most of the charge being shared between the two oxygens shown by the heavy red shading in this diagram. If there wasn't any delocalisation, one of the oxygens would have a full charge which would be very attractive towards hydrogen ions.
With delocalisation, that charge is spread over two oxygen atoms, and neither will be as attractive to a hydrogen ion as if one of the oxygens carried the whole charge. That means that the ethanoate ion won't take up a hydrogen ion as easily as it would if there wasn't any delocalisation. Because some of it stays ionised, the formation of the hydrogen ions means that it is acidic. In the phenoxide ion , the single oxygen atom is still the most electronegative thing present, and the delocalised system will be heavily distorted towards it.
That still leaves the oxygen atom with most of its negative charge. What delocalisation there is makes the phenoxide ion more stable than it would otherwise be, and so phenol is acidic to an extent.
However, the delocalisation hasn't shared the charge around very effectively. There is still lots of negative charge around the oxygen to which hydrogen ions will be attracted - and so the phenol will readily re-form. Phenol is therefore only very weakly acidic.
If the hydrogen-oxygen bond breaks to release a hydrogen ion, an ethoxide ion is formed:. This has nothing at all going for it. There is no way of delocalising the negative charge, which remains firmly on the oxygen atom. That intense negative charge will be highly attractive towards hydrogen ions, and so the ethanol will instantly re-form.
You might think that all carboxylic acids would have the same strength because each depends on the delocalisation of the negative charge around the -COO - group to make the anion more stable, and so more reluctant to re-combine with a hydrogen ion. In fact, the carboxylic acids have widely different acidities. Why is ethanoic acid weaker than methanoic acid? It again depends on the stability of the anions formed - on how much it is possible to delocalise the negative charge.
The less the charge is delocalised, the less stable the ion, and the weaker the acid. The only difference between this and the ethanoate ion is the presence of the CH 3 group in the ethanoate.
But that's important! Alkyl groups have a tendency to "push" electrons away from themselves. That means that there will be a small amount of extra negative charge built up on the -COO - group. Any build-up of charge will make the ion less stable, and more attractive to hydrogen ions.
Ethanoic acid is therefore weaker than methanoic acid, because it will re-form more easily from its ions. The other alkyl groups have "electron-pushing" effects very similar to the methyl group, and so the strengths of propanoic acid and butanoic acid are very similar to ethanoic acid. General Effects on Bronsted Acidity.
Cite the two general effects which are considered to influence the relative acidities of acids where only the nature of A is varied. Indicate in what sense increase or decrease they affect acidity and briefly explain why. The stronger the H-A bond, the less acidic is HA.
The more stable this anion is, the stronger the acid HA. The bond strength effect dominates. This is because the bond strength decreases greatly in a series which proceeds down a column of the periodic table, but the anion stability varies only slightly.
Anion stability dominates. This is because in a series which proceeds across arrow of the periodic table, bond strength varies relatively little, but electronegativity increases tremendously toward the right side, so that anion stability increases greatly as we go from methide to amide to hydroxide anion.
In both anions, the negative charge is on oxygen, so the resonance effect is essentially the only differentiating effect. Consequently, the attractive interaction is dominate and results in stabilization of the anion by this inductive effect. State both criteria which you are using and show precisely how they are applied. Quantitative Criterion [2 pts]. Then explain what specific aspect of each reactant molecule enables it to function as the Lewis acid or base.
Could this molecule serve as a Lewis base? Why or why not? Could it plausibly serve as a Bronsted acid? Although the boron is negatively charged, it has a filled second main shell and no other electrons.
Stereoisomers which are not mirror images-- diastereoisomers. Please feel free to ask your queries here. Win exciting gifts by answering the questions on Discussion Forum. So help discuss any query on askiitians forum and become an Elite Expert League askiitian. Please choose valid name.
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