These are oxidation reactions which also involve the cleavage of carbon-carbon bonds, with the oxidation occurring at both ends. Some will involve complete separation of 2 oxidised fragments and others will leave them connected together. Cleavage of Single Bonds i. 1,2-diols with Lead Tetra-acetate This reaction can also be carried out with NaIO4 instead of Pb(OAc)4. ii. Ketones … Read more
It is not the aim of this section to catalogue all means of oxidation for every compound imaginable, as this would be a mammoth task for both reader and writer (!), and furthermore quite unnecessary. The oxidations included here are the more commonly encountered reagents and functional groups, but should provide a general understanding of the processes involved in oxidation. To work from … Read more
Claisen A [3,3]-sigmatropic rearrangement (see Pericyclics). The driving force for the reaction is formation of the strong C=O bond Cope – similar to Claisen Also a [3,3]-sigmatropic rearrangement. The driving force in this case is opening of the strained four membered ring.
A rearrangement is an intramolecular reaction – i.e. a single molecule reacting with no external input. The topic of rearrangements is extremely nebulous and hence very difficult to cover systematically. Therefore the best approach is to look through the following few pages of (mostly) well-known rearrangements and try to deduce your own patterns and similarities. The theme … Read more
There are four major categories into which organic reactions fall. These are: Substitution Addition Elimination Rearrangement Substitution To deal with 1. first, substitution usually occurs on carbon. There are two sub-categories of this type: nucleophilic, and electrophilic. This is an example of electrophilic substitution (nitration of benzene): Below is a characteristic example of nucleophilic substitution: NC– is the … Read more
Whereas electrophiles have areas of electron deficiency, nucleophiles have areas that are electron rich. A nucleophilic “nucleus-loving” species will tend to attack electron-deficient areas.e.g.: Chloromethane (left) has an electron deficient carbon atom due to the presence of the inductively withdrawing chlorine atom. This is therefore most readily attacked by negatively charged species (OH–, CN– etc.), or by species … Read more
In our discussion of inductive and mesomeric effects, we have covered the concept that certain groups donate or withdraw electrons. This has the effect of making areas of molecules electron rich or poor, and this in turn will clearly influence their reactivity with other molecules. An example of an electron rich molecule is the phenoxide ion shown above. Clearly, this is … Read more
The hybridisation and therefore shape of a radical can be anywhere between sp3 and sp2, although the latter is the more common (with the unpaired electron in the p orbital) – there is some preference for it, shown by the difficulty of forming radicals in bridged species that cannot reach sp2 hybridisation. Radicals are not particularly stable in general, as … Read more
A radical is a highly reactive species which has one unpaired electron. They tend to be formed by homolytic fission of single bonds – this is in contrast to the heterolytic fission which dominates the chemistry of nucleophiles and electrophile – as shown below; In the gas phase, this bond-breaking is always more energetically favourable than the alternative heterolytic fission … Read more
It may be useful to refer to the physical chemistry sections on orbital theory and “electron in a box” diagrams before continuing with this section if they are not familiar concepts. The analogy of the harmonics (standing waves) of a piece of string fastened at both ends to an electron in an energy level is useful in this instance. … Read more