benzene Flashcards
What is benzene
C6H6
Properties of benzene
Highly flammable
Sweet-smelling
Found naturally in crude oil
A carcinogen
Is benzene reactive or unreactive
unreactive
What are arenes
hydrocarbons based on benzene
similarities between Kekule and delocalised model
- overlap of p orbitals
- Pi bond above and below
diffrences beterrn kekule and delocalised model
- kekuke has alternating pi bonds,localised electrons
- delocalised pi electrons spread around ring
3 pieces of evidence supporting delocalised model of benzene
- bond length is not single of double bond length
- Hydrogenation is less exothermic than expected
- benzene does not react with bromine
-OH with benzene ring name
phenol
-NH2 with benzene ring name
phenylamine
why is it harder for benzene to react with bromine
The delocalised electrons above and below the plane are very stable.
- spread out the negative charge
- addition reaction would break ring
what can a halogen carrier be used to do
add a halogen atom onto the benzene ring
Types of halogen carrier
AlCl3 or FeBr3
What are acyl chlorides
like COOH but OH replaced by Cl
Why is phenol less soluble than water
presence of a non polar benzene ring
What type of acid is a phenol
Weak acid
alcohols, phenol, carboxylic acid acidity from least to most
Alcohol,phenol,carboxilyic acid
How can you show phenol is a weak acid
Reacts with strong base (NAOH), doesnt react with carbonates
How to distinguish between a phenol and carboxylic acid
React with sodium carbonate, carboxilyic acid will make CO2
What does phenol and bromine make
2,4,6 tribromophenol and HBR
What does the nitration of phenol produce
2 and 4 nitro phenol and water
Why are phenols more reactive than benzene
lone pair of electrons from the oxygen p-orbital donated to the pi system of the phenol. Increases electron density, attracts electrophiles more strongly
What directing group is the -NH2 group
2 or 4
What directing group is the -NO2 group
3
What is the alkylation of benzene
sub of a hydrogen atom to an alkyl
Why are all carbon carbon bonds the same length in a benzene
Each carbon atom forms single covalent bonds to the carbon on either side
All the carbon carbon bond lengths r the same
How do rings form around benzene
Unpaired electron on each carbon atom is in a p orbital that sticks out above and below the plane
The p orbitals on each carbon atom combine to form a ring of delocalised electrons
What does a lower enthalpy change for benzene mean
More energy needed to break the bond than the other so less reactive
When is phenyl used to name benzene
attached to an alkyl chain with a functional group or 7 or more carbon atoms
COOH attached to a benzene name
benzoic acid
CHO attached to benzene name
benzaldehyde
A student adds bromine water to a solution of phenol.
What would the student see during this reaction?
Bromine water goes from orange to colourless and a white precipitate is formed.
What is the number of sigma bonds in a benzene molecule?
12
Difference between Kekule and delocalised in terms if a pi bond
Kekule - 3 pi bonds with 2 electrons localised
-delocalised - 1 pi ring with 6 electrons
