aromatics Flashcards
what is ipso ortho meta and para position on a benzene ring
ipso is the carbon with the attachment
ortho is next to the attachment
meta is one away
para is 2 away
what is the length of a carbon carbon bond in a benzene ring
1.39 angstroms (A with circle on top)
6 pi electrons, all c shifts are the same (128.5), stability from 6 pi electrons
describe the electrophilic aromatic substitution mechanism
addition of electrophile then loss of proton to restore double bond
equation of the formation of a nitronium ion in the nitration of benzene
HNO3+H2SO4–>NO2+ +HSO4-+H2O
nitric acid+sulfuric acid–>nitronium ion+hydrogen sulphate+water
compare what happens when you react phenol with bromine and when you react benzene with bromine and why
phenol+bromine=bromination
benzene+bromine= no reaction, needs lewis acid catalyst
oxygen substituents activate a benzene ring
OH group in phenol activates the ring towards electrophilic attack and is ortho/para directing
why is nitrogen a stronger activator than oxygen
nitrogen is less electronegative, the lone pair is higher in energy so more available to interact with the pi system
how to prevent oversubstitution in alanine (benzene with NH2)
make alanine less reactive by acylating the amine, this prevents the lone pair on N from interacting so strongly with the pi system, decreases reaction rate but maintains the ortho para directing effect
name 3 groups that are ortho/para directing
OH, NH2, alkyl groups
more electron density in the ortho para positions
what is the structure of toluene
benzene ring with methyl group
why doesnt the elcetrophile attack toluene at the meta position
the charged is still delocalised but none are in the tertiary position/no tertiary carbocation is formed so there is no stabilisation by the alkyl group possible, unfavourable intermediate is formed
give example of a substituent that is meta directing
Me3N/trimethyl ammonium, tri fluromethyl group
