Benzene Formula C 6 H 6 unsaturated Original

Benzene Formula C 6 H 6 unsaturated Original slide prepared for the

Benzene • Its molecular formula, C 6 H 6 , was established in 1834, after the compound's discovery by Faraday. • The formula of benzene (C 6 H 6) caused a mystery for many years after its discovery, as no explanation had been found that could account for all the bonds — carbon usually forms four single bonds and hydrogen one. • The chemist Friedrich August Kekulé was the first to deduce the ring structure of benzene (1865). • The cyclic nature of benzene was confirmed by the crystallographer Kathleen Lonsdale. • Original slide prepared for the

Benzene • Using X-ray diffraction, researchers discovered that all of the carbon-carbon bonds in benzene are of the same length, and it is known that a single bond is longer than a double bond. • In addition, the bond length, the distance between the two bonded atoms in benzene is greater than a double bond, but shorter than a single bond. • There seemed to be in effect, a bond a half between each carbon. Original slide prepared for the

Benzene • Benzene is also a planar molecule (all the atoms lie in one plane). Each carbon atom is bonded to its neighbor with one electron from each atom. Since each atom has two neighbors, this uses two electrons from each atom. • Another electron from each carbon is used to bond the hydrogen attached to it. • The remaining six electrons orbit the atomic nuclei at right angles to the plane of the ring and also overlap each other, consequently blurring their orbits both above and below the ring ( 3 electrons in upper ring and 3 electrons in down ring). Original slide prepared for the

Benzene • As a result, the electrons are shared equally between the carbon atoms and exist as two clouds, one above and one below the plane of the carbon ring. • Since these latter six electrons are not confined to specific carbon atoms, they are said to be delocalised. • This is usually represented in structural formula as a hexagon with a circle in the centre to represent the shared nature of the electrons Original slide prepared for the

Bonding in benzene H H C C C C H 6 electrons in a delocalised bond C H above and below the plane of the atoms H Original slide prepared for the

Benzene References Steve Lewis for the Royal Society of Chemistry Original slide prepared for the