The main type of reaction that alkenes undergo is addition. This is not a trick, it is as simple as it sounds: an addition reaction is where two molecules react together completely to form one product (and only one product). e.g.: Above is shown the reaction of ethene and hydrogen bromide. The reaction above is an … Read more
We know from our discussion of hybridisation, that the overlap of two sp2 orbitals and the additional overlap of two p orbitals forms a double bond. A double bond can be considered as a functional group, just as a single bond can. Molecules containing a C-C double bond are known as alkenes. However, unlike alkanes, which were very unreactive, alkenes can react … Read more
The carbon carbon bond (C-C for short) is probably one of the simplest functional groups. A functional group is a group of atoms (or sometimes just one atom) that have a characteristic chemical property. We have already seen that a C-C single bond is formed with sp3 hybridisation. The name of the group of molecules that contain only C-C single bonds and C-H … Read more
Esters can be hydrolysed by either aqueous solutions of acid or base. The products in both cases are an alcohol and a carboxylic acid. Below is shown the mechanism for acidic ester hydrolysis: Basic hydrolysis proceeds via a tetrahedral intermediate: The addition of the –OH nucleophile causes the intermediate to become tetrahedral.
As with acids, there are two types of base catalysis; specific and general. Specific Base Catalysis With specific base catalysis, the rate is again found to be directly related to the pH. The only species capable of catalysing the reaction is OH–. An example of a base catalysed reaction: This is the reverse of an aldol … Read more
Catalysis provides a reaction a lower energy pathway, so that the reaction proceeds at a greater rate. Acids can act as catalysts in certain situations. There are two types of acid catalysis; Specific Acid Catalysis and General Acid Catalysis. Specific Acid Catalysis (SAC) This is acid catalysis involving only the H30+ (hydroxonium) ion. Characteristically, it can be detected because the rate is … Read more
Two very important bases in organic chemistry are pyrrole and pyridine. These are heterocyclic bases. Firstly, what is a heterocycle? A heterocycle is a cyclic compound with a heteratom in the ring. A heteroatom in this context is any atom other than carbon. Pyrrole is a 5 membered ring containing a nitrogen atom: Pyrrole has some signs of aromaticity, as we … Read more
By way of introduction, let us first consider the simplest aromatic base, aniline: As you can see, aniline has resonance forms which lower the energy of the normal form of aniline. This resonance is allowed because the nitrogen lone pair is in an sp2 hybridised orbital, and can therefore overlap with the pi orbital system of the benzene ring. However upon protonation, no resonance stabilisation is available: The net … Read more
If we attach electron withdrawing groups to an amine, we can significantly reduce its basicity by removing the tendency for the electron pair of the nitrogen to attack a proton. e.g.: The species shown above is not very basic at all due to the electron withdrawing groups. The analogous species with three CF3 groups is practically not basic at … Read more
The trends of bases of the type NR3, where R is an alkyl group or hydrogen, can be explained quite well, and quite simply. The first point to note is that the strength of a base of this type is related to the availability of the electron pair on the nitrogen atom (as it is this pair that will attack … Read more