University:
University of Wolverhampton
Course:
4PY019 | Pharmacy
Academic year:

2024
Views:

416

Pages:

2
Author:

Sara

- all 6 carbon are sp2 hybridized with p-orbital perpendicular to the plane of the Why is benzene unusually stable for an ring unsaturated compound ? - partial overlap of p-orbitals allows electrons to delocalise around the entire ring What makes a molecule aromatic ? 1. cyclic 2. planar 3. cyclically conjugated 4. possess 4n+2 pi electrons 5. possess a induced ring current when placed in magnetic field benzene structure flat regular hexagon - C-C bonds lengths 1.39 A - C-C-C bond angles 120 degrees i) alkyl group 'activates' the ring for further attack and the 2nd group substitutes Why is friedel-crafts alkylation generally easier not useful ? ii) when primary alkyl halides are used, electrophile may rearrange to form unexpected products i) acyl group has deactivating influence Why is friedel-crafts acylation more use- on the ring and further substitutions are ful in comparison to alkylation ? inhibited ii) ketones can be easily reduced i) the rate at which further substitutions a substituent on benzene affects what ? occur ii) the position of a further substitution Activating substituents - examples : NH2 + OH - donate e- into the benzene ring making it more electron dense + reactive towards electrophiles - increases rate of reaction Deactivating substituents - examples : NO2 - withdraw e- from the benzene ring making it less electron dense + less reactive 1/2 towards electrophiles - decreases rate of reaction The electron withdrawing/donating nature of the substituent can be contributed by what two effects ? - resonance - inductive inductive effect - electron donation or withdrawal through sigma bonds > electronegative elements (N, O, S, Halogens) = -ve I effect > electropositive elements (alkyl groups + metals) = +ive I effect resonance effect - electron donation or withdrawal through pi bonds > electron withdrawing groups (C=O, CN) exert -ve R effect > electron donating groups (OH, NH2) exert +ve R effect - although they have L.P of e- (like acwhy are the halogens likely deactivating tivating substituents) due to the atoms substituents ? electronegativity What do activating substituents afford ? - ortho/para disubstituted benzenes what do deactivating substituents afford ? - meta disubstituted benzenes (apart from halogens) 2/2