Chapter 25 Flashcards
What is benzene?
Benzene is an aromatic compound with six carbons atoms joined in a ring and formula C6H6
What is the kekule model of benzene? Draw it
In 1865 German chemistry Kekulé suggested benzene is made up of a planar ring of carbon atoms with alternating single and double bonds
Diagram
What facts disprove the kekulé model?
1) if benzene contained the c=c it should undergo electrophilic addition (eg decolourises bromine water) but it doesn’t
2) if Kekulé was correct you’d expect 3c-c bonds of length 154 pm and 3 c=c bonds of length 134 pm but in reality all bonds are 139 pm
3) if Kekulé was correct you’d expect benzene with three double bonds to have three times the enthalpy change of hydrogenation of cyclohexene with one double bond. You’d expect it to be three times -120 yet it is only -208
Draw and explain the delocalized model of benzene
Each carbon in benzene uses 3 of its 4 electrons to make 3 sigma bonds
each carbon has one electron in a p orbital at a right angle to the plane
Adjacent p orbital electrons overlap sideways creating pi bonds
this system of pi barns creates a ring of electron density above and below the plane which are delocalised
Which aromatic compounds are named as substituted benzene rings and give an example
Alkyl groups halogens and nitro groups for example ethyl benzene chlorobenzene or nitrobenzene
Which aromatix compounds are named as a compound with a phenyl group attached and give an example
Alkyl chains with a functional group or compounds with 7 or more carbons are named as compounds with the phenyl group attached such as phenyl ethanone or phenyl octane
How do you name an aromatic compounds with more than one functional group
If all the functional groups are the same pick any and count round the way which give you the smallest numbers if there are different functional groups start with The group which gives its suffix
Name the conditions required for the nitration of benzene
50°C and a sulphuric acid catalyst
Draw all three parts of the mechanism for nitration of benzene
Mechanism In notes
Name the conditions required for the halogenation of benzene
A halogen carrier FECL3 and room temperature
Draw all three parts of the mechanism for the halogenation of benzene
Mechanism in book
Name the conditions for the alkylation and acylation of benzene
Reflux and aluminium chlorideAlCl3
Draw the equation for the alkylation of benzene to ethyl benzene
in book
Draw the reaction of the acylation of benzene to phenyl ethanone
in book
What is an acyl group
A carbon double bond it to an oxygen
Draw the functional group for an aldehyde
CHO
Draw the functional group for ketone
COC
Draw the functional group for in amine
NH2
Draw the functional group for a carboxylic acid
COOH
Draw the functional great for an Ester
COOC
Compare the reactivity of alkenes with benzene In terms of localised and delocalised electrons
Alkanes decolourise bromine water in electrophilic addition reaction because the pi bond contains localised electrons which induce a dipole in the nonpolar bromine enabling it to act as an electrophile.
Benzene does not react very mean unless the halogen carrier catalyst is present because benzene has a delocalised pie ring of electrons which are less dense and localised there is insufficient density to induce a dipole
What is Phenol
Phenol is an organic chemical containing a hydroxyl functional group directly bonded to an aromatic ring
What type of acid is phenol and why
Phenol is a weak acid because it partially dissociates in water
How can you tell phenol is more acidic than alcohols but less than carboxylic acid
Ethanol does not react with sodium hydroxide a strong base or sodium carbonate a weak base
Phenols and carboxylic acids react with sodium hydroxide a strong base
Only carboxylic acids are strong enough to react with sodium carbonate a weak base
State the conditions and draw the reaction for the bromination of phenol
Conditions room temperature and textbook
State the conditions and draw the mechanism for the nitration of Phenol
Conditions room temperature mechanism in textbook two products
Compare the reactivity of Phenol and benzene
Bromine and nitric acid react more readily with phenol than benzene because the lone pair from the OH oxygen p orbital is donated to the pie system increasing electron density attracting Electrofiles
What is a directing group
A functional group which directs substituents to certain positions
What is an electron donating group
An electron donating group have electrons in orbitals overlap with the delocalised ring and increase its electron density at carbon is 24 and six so electricals are most likely to react here and direct substituents to these positions
Give two examples of electron donating groups
0H and NH2
What is an electron withdrawing group
An electron withdrawing group don’t have any orbitals which overlap with the delocalised ring and or electronegative so withdraws electron density from the ring at carbon 2 4 and six so directing them to carbon three and five
Example of an electron withdrawing group
NO2
Name and draw four exceptions to the naming of aromatic compounds
Benzoic acid, phenylamine, benzaldehyde and phenol
