Benzene and Its Compounds Flashcards
compound with one or more benzene rings
arenes
benzene compounds also known as
aryl/aromatic
describe the benzene ring
each carbon benzene is sp2 hybridised = delocalised electrons
benzene shape is planar (120 degrees)
overlap of p orbitals above and below ring
delocalised electrons in pi bonds spread over all six carbon atoms
describe kekule structure
benzene perfectly symmetrical hexagonal structure BUT C=C short
benzene cannot undergo addition reaction BUT structure has double bonds
what type of reaction do benzene undergo
electrophilic substitution
why does benzene only undergo certain reactions
high electron density
can only react with electrophiles but need halogen carrier
stable = pi bonding system
why is alkenes able to react whereas benzenes cannot
higher electron density
observation when arenes are combusted
smoky flames
describe halogenation of benzene (benzene + Br2)
anhydrous iron (III) bromine/chlorine catalyst electrophile (Br+) made by FeBr3 polarise Br2 electrophile and benzene react to form positive ion which turns into neutral molecule
draw the mechanism of benzene + Br2
picture
how do we get 4- chloromethyl benzene
chlorine gas and anhydrous aluminium chloride catalyst
halogenmethyl-benzene
which positions are activated with methylbenzene and cl2/br2
2,4,6 (excess)
OR 2/4
how do we get chloromethylbenzene ( substitution in methylchain)
UV light
chlorine gas
boiling methyl benzene
conditions for nitration of benzene
Concentrated nitric acid
Concentrated sulfuric acid
Reflux
55C
describe nitration of benzene process
making electrophile (NO2+) by HNO3 + H2SO4 high electron dense pi bonding attracts electrophile pair of electrons donate
what positions do NO2 group activate
3, 5 and deactivates 2,4
describe process of alkylation of benzene
alcl3 catalyst + halogenoalkane
carbocation added to benzene ring
which positions do carbocations substitute into methylbenzene
1,3 -
1,4 -
higher temperature produced more 1,3 -
describe hydrogenation of alkylbenzene (reduction)
nickel catalyst
150 degrees
hydrogen gas
alkylbenzene + hydrogen gas
→ cyclohexane
how are side chains oxidised
reflux in acidified potassium manganate (VII)/acidified potassium dichromate + dilute h2so4
products of oxidising side chains on benzene
carboxylic acid
describe phenol
high melting point
slightly soluble due to hydrogen bonding OH
weakly acidic
more reactive than benzene
why is phenol so reactive
oxygen lone pair delocalised in ring
greater electron density around ring
benzene ring is activated
attracts electrophiles
rate on weak acidity
water
ethanol
phenol
phenol is the strongest
ethanol is the weakest
comment on dissociation with weak acids/strong acids
weak partially dissociates - some stays as acid and some stays as ions
strong completerly dissociates
why is phenol a weak acid (don’t be confused with reactivity)
phenoxide ion has negative charge spread - reduces charge density and negative ion is stable = stays as ions
why is phenol a strong acid than ethanol
ethanol has electron donating group that concentrates negative charge on oxygen - making it more attracted to hydrogen and able to reform
what are the reactions with phenols (4)
Phenol + NaOH → salt + water
2Phenol + Na → 2salt + hydrogen gas
Phenol + Na2CO3 → NaHCO3 + sodium phenoxide
Phenol + 3Br2 → 2,4,6-tribromophenol (white ppt.) + 3HBr
how do you produce 2,4,6 trinitrophenol
room temperature
dilute nitric acid
what are electron donating groups
alkyl groups
what are electron withdrawing groups
electronegative groups
