Spectroscopic methods are destined to determine the composition of samples containing one or several species on the basis of their energy levels. We have seen that the electrons of atoms don’t have access to any value of energy. They are limited to a few values of energy, the energy orbital’s/levels 1s, 2s, 2p, etc, on […]
Posts in the College – Main subjects category:
Chapter 11 : Reactions of substitution on aromatic cycles
Aromatic cycles, such as the benzene, are very stable because of their energy of resonance. As a result, it is very difficult to “open” the cycle by an usual reaction of addition. Instead of addition reactions, we observe reactions of substitution. The mechanism involves two steps. the first step is the electrophile attack of one […]
Chapter 10 : Reactions of carboxylic acids and their derivatives
All the atoms of carboxylic acids groups have a specific character. The group is thus ambident: it possesses two or more alternative and strongly interacting distinguishable reactive centres. It has acidic and basic properties. A carboxylic acid is more acid than the corresponding alcohol because the conjugated base, the carboxylate, is stabilised by resonance (pKa≈5 […]
Chapter 9 : carbanions in α of carbonyl
In the previous section, we discussed the possible reaction on the carbonyl group of organic molecules. The carbon is an electrophile and the oxygen is a nucleophile. Yet, the presence of a carbonyl can imply other processes. The hydrogen’s that are on a carbon neighbour of a carbonyl group, i.e. the carbon in α of […]
Chapter 8 : Reactions of elimination
A reaction of elimination is a reaction during which one molecule loses two fragments A and B as a neutral substrate AB. The two fragments A and B that are removed can be removed from the same carbon, in which case we talk about a 1,1 elimination, from two adjacent carbons (1,2 elimination or beta […]
Chapter 7 : Electrophile additions on alkenes and alkynes
The interest of electrophile additions on C=C liaisons is to transform two sp2 carbons into two sp3 carbons and to add a chain or a group on the existing molecule. As two carbons are involved in the reaction, the addition of the new group can give several products, with more or less (stereo)selectivity. Moreover, the […]
Chapter 6: Polymers
Nowadays, we find polymers everywhere. They can be solid or flexible, resist to low or high temperatures but are generally lighter than the materials they replace. For instance, wood or metallic chairs are advantageously replaced by plastic chairs. Plastic bags are in every shop (yet also in oceans or forests) and can support heavy charges […]
Chapter 1 : stem cells
What is a stem cell? Ultimately, every cell in the human body can be traced back to a fertilized egg that came into existence from the union of egg and sperm. But the body is made up of over hundreds of different types of cells. All of these cell types come from a pool of […]
Chapter 5 : Kinetics – speed of reaction
Kinetics Kinetics is a field of the chemistry that studies the speed of reactions. The speed of a reaction can depend on the conditions of the reaction. For instance, when we put H2(g) and O2(g) we don’t produce water spontaneously. This reaction has a very negative ΔG0. However, if we produce a spark, the reaction […]
Chapter 4 : Kinetics – Equilibrium
Chemical kinetics is the study of the speed of reactions. The speed of reaction is determined by the variation of the quantity of species by unit of time. Usually, we consider the concentrations for species in solution and we consider pressures for gases. The speed of a reaction is rarely constant and is positive until […]