Aromatic compounds Flashcards
Definition of sigma bond
A bond formed by the direct overlap of orbitals between bonding atoms
Definition of pi bond
A bond formed by the sideways overlap of two p orbitals
Electron density is above and below the plane of the molecule
Empirical formula of benzene
CH
Molecular formula of benzene
C6H6
Benzene properties
Colourless
Sweet smelling
Flammable liquid
Where is benzene naturally found?
In crude oil
What is negative thing is benzene classified as ?
Carcinogen
What reaction does Kekulé’s structure undergo that benzene doesn’t, what is the observation with both? (Disproving Kekulé’s)
Electrophilic addition reaction with bromine water
Kekulé;
Bromine water (orange) + kekulé (alkene) –> bromoalkane solution (colourless
No reaction with benzene
Benzene has lower chemical reactivity than predicted by Kekulé’s
Draw the hydrogenation of cyclohexene with one double bond and state the enthalpy change of hydrogenation
Draw the hydrogenation of benzene and state the enthalpy change of hydrogenation
What is different about the enthalpy changes of hydrogenation and how does this disprove Kekulé’s structure
Enthalpy change of hydrogenation of benzene is less exothermic than expected from Kekulé’s structure
What is different about the bond lengths in benzene and Kekulé’s structure?
Kekulé’s structure has alternating bond lengths
carbon carbon double bonds are shorter than single bonds so Kekulé’s structure is asymmetrical
Benzene has all equal bond lengths and bond angle of 120
What method is used to identify carbon lengths and bond angles in Kekulé’s and benzene?
X-ray crystallography
What does the spreading of electrons do to the molecule?
stabilises it
Explain how the delocalised model forms with drawings- structure of benzene
Each of the 6 carbons donate 1 electron from its p-orbital
These electrons combine to form a delocalised ring above and below the plane of the molecule
(P orbitals overlap forming this cloud)
Do alkenes have localised or delocalised electrons in their pi bonds? Does benzene have localised or delocalised electrons in pi bonds?What does this mean
Alkenes-localised
Benzene- delocalised
Electron density is higher in alkenes
Explains higher reactivity of alkenes and the relative stability of benzene
Describe arenes burning in air
What other organic compound can burn similarly
Characteristically sooty flames
Soot is unburnt carbon as a result of the high proportion of carbon that arenes contain
Long-chained alkanes burn with sooty flame due to increased percentage carbon content not due to unsaturation
Define arene
Aromatic hydrocarbons that contain one or more benzene rings
Name
R-CH3
Methyl
Name
R-CH2CH3
Ethyl
Name
R-OH
Hydroxy
OR
-ol
Name
R-NO2
Nitro
Name
R-NH2
Amino
OR
-Amine
Name
R-CN
Cyano
-nitrile
Name
R-F
R-Cl
R-I
R-Br
Fluoro
Chloro
Bromo
Iodo
Root of the name is benzene when group attached to the benzene ring is:
An alkyl group
Halogen
Nitro group
Carboxylic acid
Name and give molecular formula of:
Name and give molecular formula of:
Name and give molecular formula of:
Name and give molecular formula of:
Name and give molecular formula of:
After how many carbons is the aromatic compound no longer named an Xbenzene?
What is named instead?
6
Phenyl-substituted alkane
Name this:
4-phenylnonane
When is phenyl ALSO used to name a compund?
When the group added to the benzene ring affects its overall chemistry
Name this:
Iodobenzene
Draw propylbenzene
Name:
benzoic acid
Name:
Methylbenzoate
Double substituted benzene rules:
Names of prefix in alphabetical order
Keep numbers as low as possible
Methyl group usually carbon 1 otherwise use higher Mr value
Name:
1,4-dibromobenzene
Name:
1,3,5-trichlorobenzene
Draw
1,2-dibromobenzene
Draw
1,3,5-tribromo-2,4,6-trichlorobenzene
Draw
2-amino-1,3-dimethylbenzene
Name:
2,4,6-trinitromethylbenzene
If you add bromine water to alkene what do you see?
Draw the equation
Orange to colourless
Describe electrophilic addition of alkenes and draw mechanism
Pi-electron pair from the double bond is attracted to the bromine and the double bond breaks.
New bond formed between a carbon and a bromine forming a carbocation.
Bond between the two Br atoms breaks by heterolytic fission Br- formed.
Br- attracted to the intermediate carbocation and a covalent bond is formed
Generic mechanism of electrophilic substitution
label the unstable intermediate
Overall reaction of preparation of nitrobenzene from benzene
Nitration of benzene
Generation of the electrophile
Nitration of benzene
Reaction mechanism
Nitration of benzene
Regeneration of the catalyst
Overall equation for the monosubstitution of bromine onto a benzene ring
Halogenation of benzene
Generation of the electrophile
Halogenation of benzene
Reaction mechanism
Halogenation of benzene
Regeneration of the catalyst
Reaction equation for chlorination of benzene
Friedel-crafts alkykation diagram
Friedel-crafts acylation diagram
Methylation of benzene overall equation
Methylation
Electrophile generation
Methylation
Mechanism
Methylation
Regeneration of catalyst
General structural formula of acyl chloride
Overall equation of benzene with ethanoyl chloride
Acylation
Electrophile generation
Acylation
Mechanism
Acylation
Regeneration of catalyst
Overall equation of phenol dissociating H
Overall equation of phenol reacting with sodium hydroxide
Describe conditions needed for bromination of phenol draw overall equation
name product and observation
No catalyst
Bromine molecule
Room temperature
White precipitate of 2,4,6-tribromophenol
Equation for the reaction between phenol and chlorine to make TCP
Describe conditions of nitration of phenol
Draw overall equation including isomers
Room temperature
Dilute nitric acid
No catalyst
Draw ortho dichlorobenzene
Draw meta dichlorobenzene
Draw para dichlorobenzene
