Why is methylamine stronger than ammonia

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. Since ethanol is very poor at losing hydrogen ions, it is hardly acidic at all.

You might think that all carboxylic acids would have the same strength because each depends on the delocalization 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. Remember that the higher the value for pK a , the weaker the acid is. 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.

The acids can be strengthened by pulling charge away from the -COO - end. You can do this by attaching electronegative atoms like chlorine to the chain. As the next table shows, the more chlorines you can attach the better:.

Attaching different halogens also makes a difference. Fluorine is the most electronegative and so you would expect it to be most successful at pulling charge away from the -COO - end and so strengthening the acid.

Finally, notice that the effect falls off quite quickly as the attached halogen gets further away from the -COO - end. Here is what happens if you move a chlorine atom along the chain in butanoic acid. The chlorine is effective at withdrawing charge when it is next-door to the -COO - group, and much less so as it gets even one carbon further away.

Jim Clark Chemguide. This page explains why simple organic bases are basic and looks at the factors which affect their relative strengths. For A'level purposes, all the bases we are concerned with are primary amines - compounds in which one of the hydrogens in an ammonia molecule, NH 3 , is replaced either by an alkyl group or a benzene ring. All of the compounds we are concerned with are derived from ammonia and so we'll start by looking at the reason for its basic properties.

For the purposes of this topic, we are going to take the definition of a base as "a substance which combines with hydrogen ions protons ". We are going to get a measure of this by looking at how easily the bases take hydrogen ions from water molecules when they are in solution in water.

An ammonium ion is formed together with hydroxide ions. Because the ammonia is only a weak base, it doesn't hang on to the extra hydrogen ion very effectively and so the reaction is reversible. The position of equilibrium lies well to the left. The ammonia reacts as a base because of the active lone pair on the nitrogen.

Nitrogen is more electronegative than hydrogen and so attracts the bonding electrons in the ammonia molecule towards itself. That means that in addition to the lone pair, there is a build-up of negative charge around the nitrogen atom. That combination of extra negativity and active lone pair attracts the new hydrogen from the water. The strengths of weak bases are measured on the pK b scale. The smaller the number on this scale, the stronger the base is. Solution: In aniline the lone pair on N is involved in delocalization with benzene ring and is not available for protonation.

Cannot be protonated. Questions from Amines. AIIMS The correct increasing order of basic strength for the following compounds is : NEET Which of the following compounds is most basic? KEAM Which one of the following amines forms a non-acidic and alkali insoluble product with p-toluenesulphonyl chloride? Important Questions. Supplementary Books. SnapSolve Tutor. Follow us on Youtube.

Follow us on Facebook. Download APP. About SnapSolve. Join Now. Question Chemistry Class Why is methylamine stronger base than ammonia? Methylamine a stronger base than ammonia since it as a election donating group methyl. Therefore, electron density on nitrogen atom increase. Hence, it is stronger base,whereas in ammonia electron donating group is absent.