CHEM 1007 Lecture Notes - Lecture 1: Electrophilic Substitution, Electrophilic Addition, Hydrocarbon
Document Summary
Benzene is a cyclic hydrocarbon with six carbons and six hydrogens. Originally it was thought to contain alternate single and double bonds, known as the kekule structure. Double bonds are shorter than single bonds as the extra overlap of the pi orbitals bring the atom closer together. However, the benzene ring has bonds that are the same length, so it does not have alternate single and double bonds, but delocalized electrons in six overlapping orbitals. The carbon atoms form 3 covalent bonds making the angle 120 degrees and the molecule planar. Benzene does not undergo any addition reactions, as it would break up the delocalized system which is not favoured. As the delocalized electrons are electron-rich they are attacked by electrophiles. Electrophilic substitution: nitration: c6h6 + hno3 c6h5no2 + h2o. Reacts with a 50:50 mixture of conc nitric and sulphuric acid (catalyst) under reflux at 50-55 degrees to form nitrobenzene. Nitric acid is a weaker acid and acts as base.
