Benzene/Aromatic Compounds Flashcards
How do you name benzene when the functional group is on the ring?
‘Name of functional group’ ‘benzene’
eg Nitrobenzene
How do you name benzene when there’s an alkyl chain up to 6 carbons?
‘Name chain’ ‘yl’ ‘benzene’
eg pentyl benzene
How do you name benzene when there’s an alkyl chain over 6 carbons?
‘Phenyl’ ‘name of chain’
Phenyl heptane
How do you name benzene when the functional group is not directly on the ring?
‘phenyl’ ‘name of functional group’ (may also need numbers)
eg 2-chloro-1-phenyl propane
Phenyl ethanone
What are the priorities when naming benzene?
Phenol Methyl benzene Phenyl amine Benzaldehyde Benzoic acid
What is phenol?
OH directly bonded to benzene
What is methyl benzene?
CH3 directly bonded to benzene
What is phenyl amine?
NH2 directly bonded to benzene
What is benzaldehyde?
Ethanal directly bonded to benzene
What is benzoic acid?
Methanoic acid directly bonded to benzene
Why is there spare electrons in the p orbitals of carbon in benzene?
Each carbon has 4 electrons in the outer shell, 2 make sigma bonds with C, 1 is used to make a sigma bond with H, so 1 is spare
What is the shape around the carbon atoms in benzene?
120 trigonal planar
This makes benzene flat
What is the definition of a pi bond in benzene?
Sideways overlap of p orbitals on adjacent carbon atoms above and below the plane of carbon atoms in a ring.
6 electrons in pi bond across 6 C-C, delocalised
What are the negatives of kekule’s model of benzene?
Bond length
Isomers
C=C
Enthalpy of hydrogenation
How is bond length a negative of kekule’s model of benzene?
C=C are shorter so should be 2 different bond lengths but an X-ray diffraction shows all C-C bonds are all the same length in benzene
How are isomers a negative of kekule’s model of benzene?
2Br can be on the same double bond or on different ones. Tested in a number of environments you would expect different results but they react the same
How is the C=C a negative of kekule’s model of benzene?
Adding Br2 when there are double bonds makes the solution go from orange to colourless so, using kekule’s model, benzene should do this addition reaction BUT in order to get the benzene to do this you need a catalyst and it does a substitution reaction
How is the enthalpy of hydrogenation a negative of kekule’s model of benzene?
A ring with 1 C=C = -120KJ
A ring with 2 C=C = -240 KJ
So you would expect Kekule’s model to be -360KJ BUT, benzene only has an enthalpy of hydrogenation of -208KJ
Less exothermic than Kekule’s model so it is more stable
What is the molecular/emperical formula for benzene?
Molecular - C6H6
Empirical - CH
What can you add to benzene?
Cl Br Acyl chloride R group NO2
What is the catalyst when adding Cl to benzene?
AlCl3/FeCl3
What is the catalyst when adding Br to benzene?
AlBr3/FeBr3
What is the catalyst when adding a COR to benzene?
AlCl3/Br3 or FeCl3/Br3
What is the catalyst when adding an R group to benzene?
AlCl3/Br3 or FeCl3/Br3
What is the catalyst when adding NO2 to benzene?
Conc H2SO4
50 degrees celsius
How do you work out the electrophile when adding something to benzene?
Whatever you are adding with a +
Br+, Cl+ etc
What is the reagent when adding Cl to benzene?
Cl2
What is the reagent when adding Br to benzene?
Br2
What is the reagent when adding NO2 to benzene?
Conc HNO3
What is the reagent when adding an R group to benzene?
R-halogen
What is the reagent when adding COR to benzene?
Acyl chloride
R-CO-Cl
What are the 4 steps for the mechanism of reacting things with benzene?
Overall equation
Make electrophile
Curly arrow
Regenerate catalyst
What is different about phenols pi bond compared to benzene and why?
It has an extended delocalised system.
Because O and C have p orbitals. The lone pair on O is partially delocalised into pi bond which increases the electron density (8e- over 6C-C)
What is an aromatic alcohol?
When OH is directly bonded to a benzene ring
How is phenol a weak acid? (pH 3-6)
H+ ions don’t fully dissociate / the acid partially dissociates to release H+ ions in aqueous solution
What can phenol react with?
Alkali (NaOH) Metals (Na) Up to 3 Br2 Dilute HNO3 Conc HNO3
What does adding an alkali (NaOH) to phenol make?
Salt and H2O
What does adding a metal (Na) to phenol make?
Salt and H2
What does adding up to 3Br2 to phenol make?
Up to 2,4,6-tribromo phenol
What is made when adding dilute HNO3 to phenol?
Nitro phenol
NO2 either on 2 or 4 in the ratio 1:2
What is made when adding conc HNO3 to phenol?
Di/tri nitro phenol
What is observed when adding an alkali to phenol?
No fizzing (water is made)
What is observed when adding a metal to phenol?
Fizzing (H2 gas is produced)
What is observed when adding bromine to phenol?
Orange to colourless solution
White precipitate formed
Compare phenol and benzene
Phenol has H bonds with itself
Phenol has 8e- across 6C-C benzene has 6e-
Phenol has higher electron density in pi bond
Phenol can react with Br2 at room temp with no catalyst as it can induce dipoles on it
Phenol attract electrophiles more readily
Compare alkenes and benzene
Alkenes have 2e- across 1C=C benzene has 6e-
Alkenes have higher electron density in pi bond
Alkenes can react with Br2 at room temp with no catalyst as it can induce dipoles on it
Alkenes attract electrophiles more readily
What are the 3 directing groups?
NO2
NH2
OH
These have priority unless other info is given
Describe NO2 as a directing group
3,5 directing, electron withdrawing
Describe NH2 as a directing group
2,4,6 directing, electron donating
Describe OH as a directing group
2,4,6 directing, electron donating
When are things 2,4,6 directing?
Most electronegative element is directly on the ring (N in NH3 and O in OH)
When are things 3,5 directing?
Most electronegative element is 1 away from the ring (O in NO2)
How do you go from NO2 to NH2?
Sn, conc HCl, heat under reflux
What type of reaction is mainly used with benzene?
Electrophilic substitution
How can you distinguish between phenol and other acids?
Phenol won’t react with a carbonate, no fizzing
Acids will react and fizzing would occur
