Aromatic compounds, Carbonyls and Acids Flashcards
what are arenes
compounds that contain a benzene ring in their structure
what is benzene’s structure
.six carbons atoms bonded to one hydrogen atom
.forms a ring of delocalised electrons
how is the delocalised ring formed
.outer electrons from the p-orbital of the carbons are delocalised into the centre to form the ring
.results in the formation of pi bonds
.what is the evidence for benzenes structure
.the prediction for the enthalpy change of hydrogenation was at -360 KJmol-1 but ended up being -208 Kjmol-1
.all the bond lengths between carbon atoms are the same
why is benzene resistant to electrophilic addition
.as the benzene ring is too stable to be broken down
.so it undergoes electrophilic substitution
how does benzene undergo electrophilic substitution
.the ring has a high electron density making it susceptible to attack from electrophiles
what is the mechanism for the electrophilic substitution for benzene
.draw a arrow from the central ring to the positive electrophile
.this forms a positive broken ring with the electrophile being attached
.draw an arrow form the bond between the H and C to the central ring
.this forms benzene with the electrophile attached and a hydrogen ion
what is halogenation
when benzene reacts with halogens in the presence of iron(III) bromide (FeBr3)
how does halogenation work
.the iron(III) bromide acts as the halogen carrier to polarise the bromine molecule and to form a bromine atom
what is nitration
electrophilic substitution but the electrophile is NO2+ ion
how is NO2+ formed for nitration
H2SO4 reacts with HNO3 to form H2NO3+ and HSO4-
H2NO3+ forms H2O and NO2+
what is the temperature needed for the nitration of one NO2+ atom
55C
what is Friedel-crafts acylation
.when the electron ring acts as a nucleophile
.leads to the ring attacking on acyl chlorides
how does Friedel-crafts work
.R-COCl and AlCl3 react to form R-CO+ and AlCl4-
.the R-CO is used for the reaction
.at the end the H+ removed and the AlCl4- react to form AlCl3
.the reaction forms a phenyl ketone and HCl gas
why does the bromine water test not work on benzene
.the delocalised electron density of the central ring causes benzene to be resistant to bromination
what are phenols
a benzene ring with an OH group
phenol with bromine water reaction
.phenol + 3Br2 –> 2,4,6- tribromophenol + 3HBr
.forms as a white precipitate and decolourises bromine water
why can phenol react with bromine water
the lone pair of electrons of the O is delocalised to the central ring increasing electron density and so less stable and so more susceptible to attack from electrophiles
nitrification of phenol
.reacts with dilute nitric acid to form 2-nitrophenol and 4-nitrophenol
.reacts with one NO2 group in room temperature
directing effects of electron donating groups (OH and NH2)
direct to the 2nd and 4th position
directing effects of electron withdrawing groups (NO2)
direct to the 3rd position
what are carbonyl compounds
compounds containing C=O group(CO functional group)
what does the carbonyl functional group allow to happen
.allows the formation of hydrogen bonds with water
.soluble in water
what bonds do aldehydes and ketones contain
van der Waals only as they can not form hydrogen bond between themselves
