Definition: Organic chemistry is the branch of chemistry that studies the structure, properties, composition, reactions, and preparation of carbon-containing compounds.
Importance: It is significant in various fields such as medicine, biology, and environmental science due to the diversity of carbon compounds.
Structure:
Benzene (C6H6) is a cyclic hydrocarbon with a ring structure composed of six carbon atoms.
Each carbon atom is bonded to one hydrogen atom, resulting in the molecular formula C6H6.
Skeletal Formula:
The skeletal formula of benzene shows its carbon skeleton.
It is represented as a hexagon with alternating double bonds or simply as a hexagon with a circle inside, depicting resonance structures.
Resonance:
Benzene exhibits resonance, meaning the actual structure is an average of two or more valid Lewis structures.
The electrons involved in bonds are delocalized over the carbon atoms, causing equal bond lengths that are intermediate between single and double bonds.
Bond Length:
All C-C bond lengths in benzene are approximately 1.39 Å, which is shorter than a typical C-C single bond and longer than a C=C double bond.
Aromaticity:
Benzene is classified as an aromatic compound due to its stability and unique bonding, fulfilling Huckel's rule (having 4n + 2 π electrons, where n is an integer).
This stability is often referred to as "aromatic stabilization," making benzene less reactive than typical alkenes.
Physical Properties:
State: Benzene is a colorless liquid at room temperature.
Smell: It has a sweet odor and is flammable.
Solubility: Although benzene is a non-polar molecule, it is slightly soluble in water but miscible with many organic solvents.
Electrophilic Aromatic Substitution (EAS):
Benzene primarily undergoes EAS reactions rather than addition reactions due to its aromatic nature.
Common EAS reactions include:
Nitration: Introduction of a nitro group (NO2) via reaction with nitric acid (HNO3) in the presence of sulfuric acid (H2SO4).
Sulfonation: Addition of a sulfonyl group (SO3H) using sulfur trioxide (SO3).
Halogenation: Substitution of hydrogen with halogens (Cl, Br) using a Lewis acid catalyst (e.g., FeBr3).
Uses:
Benzene is a precursor for many chemicals, including:
Styrene: used to produce polystyrene plastics.
Phenol: used in the manufacture of products such as plastics and adhesives.
Cyclohexane: used in the production of nylon and other synthetic fibers.
Health Concerns:
Benzene is toxic and a known carcinogen, leading to regulations on its handling and use in industry.