Sites of organic reactions refers to the sites within molecules where there are additional or a deficit of electrons. Read all about it here on Berry Berry Easy in this post, Part 2 in the chapter of Introduction to Organic Chemistry for STPM Chemistry. It is important to understand the reaction sites in terms of why reactions occur there in terms of the bonds involved. Berry Readers would be exposed to multiple bonds, polar bonds and lewis acids and bases.
[Tips: While learning the organic reaction sites, it is important to visualise it at the same time. Imagine the molucules and visualise the reactions as it occur and how the bonds affect it. Draw it on a paper if you have difficulty visualising it. Looking at videos/schematic diagrams also helps greatly.]
STPM Chemistry Form 6 Note – Introduction of Organic Reaction (Part 2)
Sites of reactions
- Electrophiles (Greek, “electron-loving”) – electron-deficient speciesthat accept electrons in a chemical reaction. Electrophiles are Lewis acids.
- Nucleophiles (Greek, “nucleus-loving”) – electron-rich species / species with electron availability that donates electrons in a chemical reaction. Nucleophiles are Lewis bases.
- 4 types of reaction sites: multiple bonds, polar bonds and Lewis acids and bases.
A. Multiple Bonds
- Active reaction site: double bond or triple bond (electron-rich π cloud / bonds and available to species looking for electrons)
- More readily to an attacking species
B. Polar Bonds
- They are covalent bonds which have uneven sharing of electron pairs between atoms of different electronegativities (one atom of the bond is partially negative and another atom of the bond is partially positive).
- Molecules (high electron density) attract electrophiles.
C. Lewis Acids and Bases
- Lewis acid – substance that can accept a pair of electrons for sharing in a chemical reaction (electrophile).
- Lewis base – substance with an outer-shell nonbonding electron pair that can donate in a chemical reaction (nucleophiles).
D. Combination of Site Types
- Some of the reaction sites contain two or more of the structural concepts.
- Example: Formaldehyde (COH2) has carbon-oxygen double bond
- This site has a polar bond (oxygen is more electronegative than carbon, a Lewis base (unshared pairs of electrons on the oxygen) and multiple bond with a π bond.
This marks the end of Part 2 in the series of notes on the Introduction to Organic Chemistry for STPM Chemistry by Berry Berry Easy. In the next part, you’ll learn about the inductive effects in terms of positive inductive effects and negative inductive effects.