Aromatic Chemistry - Reaction with Arenes (8.2)

Question 1

What is a nucleophile?

Answer 1

• an electron rich substance attracted to an area of low electron density (loves positive charges
• e.g. Cl2, H20

Question 2

What is an electrophile?

Answer 2

• an electron poor substance attracted to an area of high electron density (loves negative charges)
• e.g. H+, NO2+

Question 3

What is benzene going to react with? Electrophiles or Nucleophiles?

Answer 3

• Electrophiles - as electrons are above and below the molecule of the plane
• electrons available for reaction

Question 4

What does SEAr stand for?

Answer 4

Electrophilic Aromatic Substitution

Question 5

What happens in Electrophilic Aromatic Substitution?

Answer 5

• a hydrogen atom = substituted for another functional group

Question 6

What are some SEAr reaction examples?

Answer 6

• nitration
• sulfonation
• halogenation
• friedel crafts alkylation

Question 7

What happens in general Electrophilic Aromatic Substitution mechanism?

Answer 7

• formation of electrophile
• benzene attacks the electrophile
• formation of carbocation ring
• reformation of aromatic ring
• regeneration of catalyst

Question 8

What happens in the nitration of benzene?

Answer 8

• reagent = nitric acid (HNO3)
• catalyst = sulfuric acid (H2SO4)
• conditions = no warmer than 50oC
• generation of the electrophile
• attack of the electrophile
• regeneration of the catalyst

Question 9

What is phenylamine?

Answer 9

• simplest aryl amine
• starting point for making other chemicals and pharmaceutical compounds
• made by the reduction of reduction of nitrobenzene (by nitration)

Question 10

What happens in the halogenation of benzene?

Answer 10

• reagent = Cl2 (Br2/I2)
• catalyst = AlCl3 (AlBr3/AlL3)
• generation of the electrophile
• attack of the electrophile
• regeneration of the catalyst

Question 11

What happens in Friedel Crafts Alkylation?

Answer 11

• reagent = R-X (e.g. CH3-Cl)
• catalyst = AlCl3
• generation of the electrophile
• attack of the electrophile
• regeneration of the catalyst

Question 12

What happens in Friedel Craft’s Acylation?

Answer 12

• reagent = R-X (e.g. CH3-Cl)
• catalyst = AlCl3
• generation of the electrophile
• attack of the electrophile
• regeneration of the catalyst
• and formation of the product

Question 13

What happens in SEAr reactions with substituted benzene?

Answer 13

• alkyl, alcohol and amine groups all push electron density into the benzene ring = the ring becomes more electron rich
• SEAr reactions can occur more easily
• making multiple reactions occur
• reactions taking place without a catalyst

Question 14

What are directing groups?

Answer 14

• methyl, phenol and amine groups

- direct substituents to the 2- and 4- positions

Question 15

What further reactions can occur with methylbenzene?

Answer 15

• free-radical substitution (in UV light) -alkane chain reacts like any alkane
• oxidation of the side chain (with alkaline KMnO4 as a reagent, & diluted H2SO4 as a catalyst (making a carboxylic acid

Question 16

What further reactions can occur with phenol?

Answer 16

• phenol = alcohol, so reacts with acyl chlorides or acid anhydrides to make esters
• does not react with carboxylic acids
• cannot be oxidised with potassium dichromate
• but oxidised with other reagents to form biologically or pharmacologically active species

Question 17

What happens in acid/base reactions of phenol?

Answer 17

• phenol = weak acid
• ions = stabilised because negative charged = delocalised into the ring
• reacts with strong bases e.g. NaOH
• does not react with sodium carbonate

Question 18

What happens in acid/base reactions of amines?

Answer 18

• the lone pair on any amine can form a dative covalent bond

- with H+ in a acid-base reaction