In its most basic form, an alkene is an electron rich species – the electrons of the π system are quite diffuse and easily polarised, forming a cloud of negative charge around the carbon atoms. This makes most alkenes attractive to electrophiles – those species that are electron deficient. The reactions they will undergo together are addition reactions – similar in overall … Read more
A mesomeric effect is an electron redistribution that occurs via a pi orbital, quite often via conjugated systems. A good example of this effect is seen in the carbonyl group: The properties of the carbonyl are not properly explained by the classical image (far left), nor by the dipole (centre), which represents the total relocation of the pi electrons; the “real” … Read more
The factors affecting the electron availability of a compound might reasonably be thought to have far-reaching consequences upon its reactivity with various compounds. For example, an area of high electron density is unlikely to be attacked by OH–, but an area of low electron density is likely to be far more susceptible to attack by … Read more
This final section of the chapter deals with a few named reactions in which enolate anions react with other carbonyl compounds as nucleophiles – so these could realistically have been placed under the nucleophilic addition chapter. These are just meant to be representative of the huge number of possibilities present for carbonyls reacting with other carbonyls – by noting the patterns and … Read more
Because of the lack of leaving group on these carbonyls (the leaving group would have to be an alkyl group leaving as a carbanion – not generally very stable), they react differently to the general reactions discussed on the previous page. The C=O bond is still polar and attractive to nucleophiles however, so they can attack here. However, it is important … Read more
A carbonyl is a molecule containing the C=O functional group. For the purposes of this chapter they will be split into 2 categories – one category will be ketones and aldehydes, the other will include pretty much everything else. To see how this breaks down; Of the latter class a couple of examples have been given – some other important carbonyls … Read more
The three types of hybrid orbitals we have seen are sp, sp2 and sp3. Hybrid Type Angle between orbitals Arrangement Example C-C Bond Strength (kJ mol-1) C-C Bond Length (Å) sp3 109° 28′ Tetrahedral Ethane (C2H6) 376 1.54 sp2 120° Trigonal planar Ethene (C2H4) 611 1.33 sp 180° Linear Ethyne (C2H2) 835 1.20 As you might … Read more
The third type of hybridisation commonly encountered in organic chemistry is sp. By extrapolation, it is obvious that this involves the use of one s orbital, and one p orbital. Let us have a look at an sp hybridised carbon atom: In this diagram, there are two unhybridised p orbitals, and two sp orbitals. The sp orbitals … Read more
Atoms bond together because in doing so, they can achieve a lower overall energy. In simple terms, making bonds releases energy, and breaking bonds requires energy. The bonds we most often come across in organic chemistry are covalent bonds. These are bonds where electron pairs are shared between atoms, usually with one electron from each pair … Read more
We now know what the orbitals of a general atom look like, but now we need to know in what order the orbitals are filled on progressing through the periodic table, so we can then make predictions about those elements. The following rules can be used to predict the lowest energy state of the electronic configuration (the ground state): … Read more