Chapter 25
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What is the molecular formula of benzene?
C₆H₆
What colour is benzene?
Colourlesss
What type of smell does benzene have?
Sweet
How flammable is benzene?
Highly flammable
What is a carcinogen?
Can cause cancer
What is the structure of benzene?
1) hexagonal ring of six carbon atoms 2) carbon atoms joined to two other carbon atoms and to one hydrogen atom
What is benzene classed as?
1) aromatic hydrocarbon 2) arene
What is the Kekulé model?
1) six membered ring of carbon atoms 2) joined by alternate single and double bonds
What is the evidence to disprove Kekulé’s model?
1) the lack of reactivity of benzene 2) the lengths of the carbon-carbon bonds in benzene 3) hydrogenation enthalpies
What do alkenes decolourise?
Bromine water
How does the lack of reactivity of benzene disprove Kekulé’s model?
1) benzene does not undergo electrophilic addition reactions 2) benzene does not decolourise bromine under normal conditions
How do the lengths of the carbon-carbon bonds in benzene disprove Kekulé’s model?
All the bonds in benzene are 0.139nm in length, between the length of a single bond, 0.153nm, and a double bond, 0.134nm
What is hydrogenation?
The addition of hydrogen to an unsaturated compound
What is the IUPAC name of the Kekulé model?
cyclohexa-1,3,5-triene
When cyclohexene is hydrogenated, how many double bonds react with hydrogen?
One
What is the structure of the delocalised model of benzene?
1) planar 2) cyclic 3) hexagonal hydrocarbon containing six carbon atoms and six hydrogen atoms
What is the bonding in the delocalised model of benzene?
1) each carbon atom uses three of its available four electrons i bonding to two other carbon atoms 2) each carbon atom has one electron in a p-orbital at right angles to the plane of the bonded carbon and hydrogen atoms 3) adjacent p-orbital electrons overlap sideways, in both directions, above and below the plane of the carbon atoms to form a ring of electron density 4) overlapping of the p-orbitals creates a system of pi-bonds which spread over all six of the carbon atoms in the ring structure 5) six electrons occupying system of pi-bonds are delocalised
What groups are prefixes to benzene?
1) short alkyl chains 2) halogens 3) nitro groups
What are aromatic compounds with one substituent group?
Monsubstituted
When is benzene considered to be substituent?
When a benzene ring is attached to an alkyl chain with a functional group or to an alkyl chain with seven or more carbon atoms
When is the prefix phenyl used instead of benzene?
When benzene is considered to be a substituent
What are the three exceptions when naming aromatic compounds?
1) Benzoic acid (benzenecarboxylic acid) 2) phenylamine 3) benzaldehyde (benzenecarbaldehyde)
How many substituent groups do disubstituted compounds have?
Two
How are substituent groups listed?
1) alphabetical order 2) using the smallest numbers possible