Aromatic compounds are divided into two categories: benzenoids (one containing benzene ring) and non-benzenoids (those not containing benzene ring), provided they follow Huckel rule. The delocalized structure of benzene also accounts for the X-ray data (all C-C bond lengths equal) and the absence of the type of isomerism shown in Fig. It means, that the distance between the same pair of atoms (e.g., C-H) may vary depending on which compound we are dealing with. 43.1. Benzene is an aromatic compound, as the C-C bonds formed in the ring are not exactly single or double, rather they are of intermediate length. σ BO = ½(B – A) = ½(2 – 0) = 1. All the carbon-carbon bond lengths in benzene are identical, 1.4 Å (1.4 × 10-10 m) Effectively bonds are in longer-shorter cycle, oscillating around some particular length. This bond length falls exactly halfway between the length of a carbon‐carbon single bond (1.46 pm) and a carbon‐carbon double bond (1.34 pm). As a result of the delocalization, benzene ring is stable, thus, reluctant to undergo addition reactions, unlike other alkenes. BO = ½(B – A) The C-C σ Bonds. Therefore, all the C-C bond lengths are the same, and the length is between single and double bond lengths. It reacts with IV in presence of aluminium chloride to form acetophenone. Building the orbital model. The C-C π Bonds. The delocalization of the electrons means that there aren’t alternating double and single bonds. Benzene has a melting point of 5.5°C and a boiling point of 80°C. Benzene is built from hydrogen atoms (1s 1) and carbon atoms (1s 2 2s 2 2p x 1 2p y 1).. Each carbon atom has to join to three other atoms (one hydrogen and two carbons) and doesn't have enough unpaired electrons to form the required number of bonds, so it needs to promote one of the 2s 2 pair into the empty 2p z orbital. Benzene has a planar structure. It has 2 bonding electrons and 0 nonbonding electrons. Fill in the blanks with appropriate words. All the carbon-carbon bond angles in benzene are identical, 120°. In addition, these studies confirm that all bond angles are equal (120°) and that the benzene molecule has a planar (flat) structure. Benzene has 6 molecular π orbitals. The actual bond length (1.395 Å) is the intermediate between the sp 2 –sp 2 single bonds (1.46 Å) and double bonds (1.33 Å). The ring structure of benzene was proposed by II .It shows III substitution reactions. An orbital model for the benzene structure. The Structure and Geometry of Benzene The bond order of a bond is half the difference between the number of bonding and antibonding electrons. All carbon atoms in benzene are I hybridised. In general, the length of the bonds is a property of a whole molecule. Benzene is toxic and is known to cause cancer with prolonged exposure. Benzene is planar molecule (or a flat molecule). The 4th bond pair of electrons from each Carbon atom is delocalised, creating a delocalised cloud of electrons above and below the plane. Benzene is an hexagonal ring in shape with bond angles of 120degrees between Carbon atoms.All the bond lengths in Benzene are equal. Each C-C σ bond is a localized bond. C-C bond length in benzene is 140 pm and C-H bond length is 109 pm. The common practice of using only one of the Lewis structures is only to make keeping track of the π electrons easy. Research conducted with X-rays has allowed us to determine that the bond length for all six C-C bonds in benzene is 142 pm.