38568
Aromatic Compounds
- Benzene
- History
- Kekule: Snake - planar, cyclic
- BUT
- Thermodynamically more stable than expected
- Releases 208 kJ per mole when reduced instead of 3*120. Resonance energy = 152 kJ per mole
- Releases 208 kJ per mole when reduced instead of 3*120. Resonance energy = 152 kJ per mole
- Bond lengths all similar
- Did not undergo electrophilic
addition → no true double bond
- SO
- Resonance Hybrid
- Each bond is between single and double
- Lower in energy than Kekule → thermochemically stable
- Each bond is between single and double
- Delocalised pi orbital system, planar
- Resonance Hybrid
- Thermodynamically more stable than expected
- BUT
- C6H6
- X Aliphatic
- X Aliphatic
- First isolated in 1825
- Kekule: Snake - planar, cyclic
- Electrophilic substitution
- Does not affect delocalisation
- Need stronger electrophiles
than those with alkene
- Nitration
- Conc HNO3,
conc H2SO4
(catalyst)
- 55 degrees
- Electrophile: NO2+
(nitronium)
- Nitro benzene
- → Phenylamine → diazonium dyes
- Not safe, side effects
- → Phenylamine → diazonium dyes
- Conc HNO3,
conc H2SO4
(catalyst)
- Halogenation
- Chlorine, Halogen carrier (catalyst)
- Reflux
- Chlorine, Halogen carrier (catalyst)
- Friedel-Crafts Reaction
- Acylation
- Reflux, 50 degrees, dry ether
- RCOX, anhydrous AlCl3
- Electrophile: RC+=O
- Reflux, 50 degrees, dry ether
- Alkylation
- RX, anhydrous AlCl3 (catalyst)
- Electrophile: R+
- Room temp, dry ether
- RX, anhydrous AlCl3 (catalyst)
- Acylation
- Further substitution
- Sulfonation
- + Fuming sulphuric acid → Benzenesulfonic acid
- Room temp
- + Fuming sulphuric acid → Benzenesulfonic acid
- Does not affect delocalisation
- Addition
- Bromine in UV light
- Free radical reaction
- Free radical reaction
- Hydrogenation with Raney nickel
catalyst, 150 degrees C
- Cyclohexane
- Cyclohexane
- Bromine in UV light
- Burns with yellow smoky flame
- History
- Phenol
- C6H5OH
- Aromatic alcohol
- Preparation
- Nitration of benzene
- Reduction of nitro benzene with Tin, Conc HCl, Reflux
- Diazotisation of phenyl amine: nitrous acid and hydrochloric acid, below 10 degrees
- Substitution of diazogroup by OH: water, warm above 10 degrees
- Substitution of diazogroup by OH: water, warm above 10 degrees
- Diazotisation of phenyl amine: nitrous acid and hydrochloric acid, below 10 degrees
- Reduction of nitro benzene with Tin, Conc HCl, Reflux
- Nitration of benzene
- More reactive than benzene as OH group activates benzene ring
- Weak acid
- Electrophilic substitution
- Without catalyst
- Further Substitution
- With Bromine water
- With dilute nitric acid
- With Bromine water
- Without catalyst
- Antiseptic, used to make polymers
- C6H5OH
- Benzene diazonium chloride
- C6H5N2+Cl-
- Preparation
- Phenylamine, nitrous acid (made in situ from sodium nitrite), hydrochloric acid
- Kept below 10 degrees to slow down decomposition of salt
- Phenylamine, nitrous acid (made in situ from sodium nitrite), hydrochloric acid
- Reactions
- Substitution of OH (hydrolysis) → phenol
- Substitution with I using KI solution, warm
- Coupling
- + NaOH + Phenol → Azo dye (N=N)
- + NaOH + Phenol → Azo dye (N=N)
- Substitution of OH (hydrolysis) → phenol
- C6H5N2+Cl-
- Any hydrocarbon
system which has a
stabilised ring of
delocalised electrons
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