benzene
- does not react with Br2 via elimination
- reacts with substitution in the presence of FeBr3 (C6H5Br)
- all hydrogens are equivalent
- planar, all bonds are sp2 hybridized and angles are 120 degrees
arene
-hydrocarbon based on the benzene ring as a structural unit
hydrogenation of benzene
-needs 3 moles of H2 (3H2) and rhodium or platinum at room temp to form cyclohexane
heats of hydrogentation
-conjugation that is cyclic has a lower than expected heat of hydrogenation, which infers that benzene is more stable than an open triene
benzene MO
- 3 = bonds
- 6 C atoms
- 6 p orbitals
- 3 bonding
- 3 antibonding
phenyl
- when benzene ring is considered as a substituent, this is its name
- abbreviated by Ph or O with line through the middle
benzyl group
- benzene ring is substituent with CH2
ex. C6H5CH2-
polycyclic aromatic hydrocarbons (PAHs)
- multiple benzene rings fused together
- cannot spin; rigid
- not water soluble
- very volatile
- increased toxicity with greater number of benzene rings
poly chloro biphenyl (PCBs)
- can have up to 10 substituents on the biphenyl
- can spin about the single bond
physical properties of benzene
- nonpolar
- insoluble in water
- less dense than water
benzylic carbon
-a carbon atom that is directly attached to a benzene ring
benzylic carbocations and radicals
-more highly stabilized than allylic carbocations/radicals (H2C=CH-)
benzylic radical
-more stable than allylic radical because the C-H bond is easier to break and has a lower value of enthalpy
(mechanism is free-radical chlorination)
chlorination of toulene
- takes place exclusively at the benzylic carbon (the carbon attached to the benzene ring)
- the benzylic hydrogen is abstracted and replaced by a Cl atom
oxidation of benzene
- Na2Cr2O7 (sodium dichromate) does not react with benzene unless it is substituted
- Na2Cr2O7 and KMnO4 are both strong oxidizing agents
- compounds must have a benzylic H to spontaneously combust
- CO2H (carboxylic acids) are the highest oxidation state possible
