arene chemistry Flashcards
what is aliphatic organic molecul e
straight or branched chain organic substances
aromatic or arene?
includes one or more ring of six carbon
atoms with delocalised bonding.
Benzene’s structure
The simplest arene is benzene.
It has the molecular formula C6H6 Its basic structure is six C atoms in a hexagonal ring, with one H atom bonded to each C atom.
Each C atom is bonded to two other C atoms and one H atom by single covalent σ-bonds. This leaves one unused electron on each C atom in a p orbital, perpendicular to the plane of the ring.
The six p electrons are delocalised in a ring structure above and below the plane of carbon atoms.
is benzene planar
Benzene is a planar molecule. The evidence suggests all the C-C bonds are the same and have a length and bond energy between a C-C single and C=C double bond.
H-C-C bond angle in benzen
120 degrees
why is benzene more thermodynamically stable than expected
The 6 pi electrons are delocalised and not arranged in 3 double bonds.
would hydrogenation value be less In a) cyclohexa-1,3-diene, b) cyclohexa-1,4-diene
In cyclohexa-1,3-diene, there would be some delocalisation and extra stability as the pi electrons are close together and so overlap. The hydrogenation value would be less negative than -240 kJ mol-1 (showing more stable)
n cyclohexa-1,4-diene, there would not be delocalisation as the pi electrons are too far apart and so don’t overlap. The hydrogenation value would be -240 kJ mol-1
how to name benzene w CA group
benzenecarboxylic acid
how to name benzene w aldehyde grp
benzaldehyde
does benzene undergo addition reactions, why?
no
would involve breaking up delocalised system
why does benzene attract electrophiles
- has high electron density
is benzene toxic
yes
it is a carcinogen (causes cancers)
why is methylbenzene less toxic
Methylbenzene is less toxic and also reacts more readily than benzene as the methyl side group releases electrons into the delocalised system making it more attractive to electrophiles.
importance of nitration of benzene
Nitration of benzene and other arenes is an important step in synthesising useful compounds e.g. explosive manufacture (like TNT, trinitrotoluene/ 2-methyl-1,3,5- trinitrobenzene) and formation of amines from which dyestuffs are manufactured.
Overall equation for formation of the electrophile for nitration of benzene, what type of reaction is it
HNO3 + 2H2SO4 +NO2 + 2HSO4- + H3O+ This is an acid-base reaction.
Reducing a nitroarene to aromatic amines: 2 ways
Reagent: Sn and HCl or Fe and HCl Conditions: Heating
Mechanism: reduction
- This reduction reaction can also be done with catalytic hydrogenation (H2 using a Ni catalyst)
benzene -> phenyl ketone conditions + reagents
- heat under reflux
- acyl chloride in presence of anhydrous chloride catalyst
how does chlorobenzene change c-cl bond
- stronger
- Typical halogenoalkane substitution and elimination reactions do not occur. Also the electron rich benzene ring will repel nucleophiles.
how does phenol change c-o, o-h bond
Delocalisation makes the C-O bond stronger and the O-H bond weaker. Phenol does not act like an alcohol- it is more acidic and does not oxidise.
