ARENES Flashcards
Explain the MP/BP of benzenes
Low BP as it has SMS that is non-polar, thus it is held together by weak idid int which requires little amt of energy to overcome
Why is ΔH of hydrogenation of benzene less exo than its kekule structure
Benzene is more energetically stable than its kekule structure due to the delocalisation of pi e- in BZ
Why is BZ less reactive towards E+ compared to alkenes
BZ and alkenes are both e-rich due to presence of pi e-
-> due to delocalised pi e- cloud in the BZ ring, BZ is resonance stablised
-> BZ becomes a weak Nu, less reactive towards E+
Why does BZ only undergo E-Sub and not E-Add
E-Sub retains its aromaticity and remain resonance stabilised, whereas E-Add will disrupt the aromaticity which is energetically unfavourable
Explain the C-C bond length in benzene compared to that in alkenes
C-C bond length in BZ is in b/w C-C bond and C=C bond due to partial double bond charcaer of C-C in BZ
Why cant Al2Cl6 be a catalyst for E-sub of X2
The Al atom is not electron deficient and cannot accept lone pair through dative bond
inductive effect
electron donating or withdrawing through SIGMA BOND
Why is H2SO4 required as catalyst for E-sub of BZ but not E-add of alkene?
Alkenes have e-rich C=C bond that attacks E+ with partial positive charges.
However due to resonance stability of BZ, E+ are too weak to rxt w BZ
thus H2SO4 rxts w HNO3 to generate NO2+ which is a much stronger E+ that can rxt w BZ
resonance effect
electron withdrawing or donating effect through overlap of p orbital
For E-Sub of Methylbenzene, why is a lower temperature(30) used instead of 55 for benzene
The activating methyl group increases the electron density of the BZ ring, making it more susceptible to e-sub, thus milder conditions are required
further substitution may occur if temp >30
definition of electrophile
electron deficient species that act as an e-pair acceptor
definition of nucleophile
electron rich species that act as an e-pair donor
Role of H2SO4 in E-sub
Bronsted Lowry Acid as it donates a proton to __ and generates strong electrophile
How to distinguish between NH2 group and CH3 group
Add KMnO4 in H2SO4 and heat in water bath
mol w/ CH3 will decolourise purple KMnO4. KMnO4 will remain purple in the mol w/ NH2
Describe the role of AlCl3 in electrophillic sub
It acts as a lewis acid catalyst that generates a stronger electrophile to react with a resonance stablised benzene ring
Formula for degree of unsaturation
(2C+2-H+N-X)/2
