18A - Benzene

What is the difference between an aliphatic and aromatic compound?

• Aliphatic - Straight/branched chain organic susbstance

• Aromatic - 1+ rings of 6 carbon atoms with delocalised bonding electrons

What are some uses of aromatic compounds?

• Fragrances

• Drugs - antibiotic, pain relief

• Plastics

• Pigment

What are some properties of benzene?

• Planar structure - so flat

• Cyclic - 6 carbon atoms bonded

• Delocalised pi electrons - make it stable

• High mp bc stable

• low bp bc non- polar, hard to dissolve in water

Name these compounds?

Name these compounds

What is the expected value for benzene and what does it show about benzene

• -360

• Benzene is more stable than the proposed structure of cyclohexan 1,3,5 triene (benzene has less energy)

What are the 2 electrophillic addition reactions benzene can undergo?

• Nitration

• Freidal - crafts acylation

What are the conditions and reagant for the nitration reaction of benzene and what is the electrophle?

• Nitric acid (HNO3)

• conc sulfuric acid

• warm

• Electrophile - NO2

In nitration of benzene why shouldn’t the temperature go above 55 degress?

Multiple substitution reactions occur which wont produce arenes

What is the combustion reaction of benzene?

C6H6 + 7.5 O2 → 6CO2 + 3H2O

What are the reagents for halogenation of benzene?

X (halogen) and FeX catalyst

What is the formula for phenols?

C6H5OH

What is the reaction of phenol with bromine water? (what does it produce and observations)

• Produce 2,4,6 tribromophenol

• white preciptate, antisepctic smell

• Brown to colourless

What is the difference between bromination of phenols compared to benzene?

• Phenol doesn’t need catalyst

• Undergoes multiple substitution reactions

Why is the reaction of bromine water more reactive with phenols than benzene?

• In phenols the lp of e- in the oxygen atom is partially delocalised into the benzene ring structure, so e- density increases

• bromine is more polarised

What can phenoles be used to make?

• plastics

• Antiseptics

• Disinfectant

• Resin for plants

Why is phenol more like to react with a haloalkane than benzene?

• Bc of lone pair on oxygen delocalises into benzene ring

• Which increases electron density

• Making phenol more susceptible to electrophillic attack