organic chem Flashcards
equation for generation of electrophile in nitration (ES)
HNO + 2H2SO4 -> NO2+ + 2HSO4- + H3O+
equation for generation of electrophile in chlorination (ES)
Cl2 + AlCl3 -> Cl+ + [AlCl4]-
OR
Cl2 + FeBr3 -> Cl+ + [FeBr3Cl]-
equation for generation of electrophile in bromination (ES)
Br2 + FeBr3 -> Br+ + [FeBr4]-
OR
Br2 + AlCl3 -> Br+ + [AlCl3Br]-
why catalyst is required for ES of benzene rings,
but not phenol, methyl benzene or phenylamine
- benzene rings need as
- contains delocalised electron cloud
- thus resonance stability
- less susceptible to ES
- others (benzene ring + OH / alkyl (e.g. CH3) / NH2)
don’t need as- they activate benzene ring for ES
- for phenol and phenylamine, lone pair of e- on O/N delocalises into benzene ring
-> increase e- density in benzene ring - for alkyl amine, alkyl grp is ED
-> increase e- density in benzene ring
- for phenol and phenylamine, lone pair of e- on O/N delocalises into benzene ring
- they activate benzene ring for ES
why benzene rings undergo ES, not EA
- addition rxn leads to loss of delocalised π e- cloud system
- requires a lot of energy
- thus EA not favoured
equation for iodoform reaction
- RCH(OH)CH3 + 4I2 + 6OH- -> RCO2- + CHI3 + 5I- + 5H2O
- RCOCH3 + 3I2 + 4OH- -> RCO2- + CHI3 + 3I- + 3H2O
equation for tollens’ test
RCHO + 2[Ag(NH3)2]+ + 3OH- -> RCO2- + 2Ag + 4NH3 + 2H2O
equation for fehling’s test
RCHO + 2Cu2+ + 5OH- -> CH3CO2- + Cu2O + 3H2O
function of (trace) KCN in NuA
- generate nucleophile CN-
(eqn: KCN -> K+ + CN-) - can be replaced by any (Bronsted) base (e.g. NaOH) which reacts with HCN to generate CN-
factors affecting ROR of NuA /
susceptibility/reactivity of substrate towards NuA and NuS
- (most important) how e- deficient the C atom in cpd is
- alkenes:
C=C bond is non-polar
-> no e- deficient site
=> not susceptible to NuA / NuS - aldehyde vs ketone:
C atom in aldehyde has fewer ED alkyl grps bonded to it
-> more e- deficient
=> more susceptible to NuA / NuS
- alkenes:
- (for NuS only) whether bond in cpd has partial double bond character
- acyl chloride (benzene ring -Cl):
lone pair on X delocalise into benzene ring
-> C-X has partial double bond character
-> C-X bond is difficult to break
=> less susceptible to NuA / NuS
- acyl chloride (benzene ring -Cl):
understanding directing effect of grps for ES
- context: during ES, e-rich benzene attacks electrophile (i.e. benzene donates e- pair to electrophile)
- thus favouring of certain C positions could be due to that C position having greatest ability to supply an e- pair to the electrophile
reason why racemic mixture is formed (or product mixture does not rotate plane-polarised light)
- happens during Sn1 and NuA
- (1) geometry around the C atom in the cpd is planar
- (2) thus the nucleophile can attack C atom from top and bottom of plane with equal probability
- (3) thus forming a racemic mixture
identifying nucleophile as the role of cpd in rxn
- cpd has atom with 1 or more lone pairs
- and it donates 1 of them to bond to an e-deficient atom in another cpd
reasons UV/heat is needed for FRS
- X-X bond is very strong (QV)
and thus requires a lot of energy to break - UV/heat provides the energy required to break the X-X bonds and form X• radicals
reason reaction continues with increasing rate after brief exposure to UV/heat has stopped
- reaction is exothermic
- heat produced increases KE of reactant molecules
- thus increasing frequency of effective collisions
- and thus increasing ROR
