Pyridine

Question 1

Pyridine bonding

Answer 1

N lp perpendicular to aromatic π-system, electron deficient, N electronegativity decreases energy of all molecular orbitals so a low energy HOMO means its less reactive towards EAS, low energy LUMO means more reactive to NAS

Question 2

Pyridine N-oxide formation

Answer 2

Pyridine and peracid or H2O2 with HoAC which forms a peracid in situ

Question 3

Pyridine N-oxide with electrophile

Answer 3

Electrophile adds para

Question 4

Pyridine N-oxide with PCl3

Answer 4

Removes oxygen and turns it back into nitrogen

Question 5

Pyridine N-oxide with POCl3

Answer 5

Adds chlorine to C2

Question 6

Pyridine N-oxide with 1. Ac2O then H3O+

Answer 6

Adds keto group to C2, adds OH to C2 giving Enol form first then tautomerises to keto form

Question 7

Pyridine nucleophilic aromatic substitution

Answer 7

2-step addition-elimination mechanism going via a tetrahedral intermediate

Question 8

ChiChibabin reaction

Answer 8

Pyridine with 1. NaNH2, toluene and heat 2. H2O, adds NH2 to C2

Question 9

Pyridines with OH on C2/C4

Answer 9

Tautomerises to pyridone

Question 10

Substituted pyridine reactions

Answer 10

Side chain bromination with N-bromosiccinimide (NMS), side chain oxidation, hydrogenation of pyridine to piperidine