9 - HETEROCYCLES

Question 1

why is pyridine a weaker base than piperidine?

Answer 1

Question 1

what are some natural and synthetic derivates of pyridine?

Answer 1

Question 2

how do orbitals affect acidity and basicity?

Answer 2

Question 3

how does electronegativity play a role in acidity/basicity?

Answer 3

Question 4

how is pyridine formed from an unsaturated 1,5-dicarbonyl compound?

Answer 4

Question 5

how is pyridine formed from a saturated 1,5-dicarbonyl compound?

Answer 5

Question 6

how is dihydropyridine reduced to aromatic pyridine by DDQ?

Answer 6

Question 7

what is the mechanism of the Hantzsch pyridine synthesis?

Answer 7

Question 8

which carbon substitution does pyridine prefer?

Answer 8

C3 substitution is preferred
this maximises the number of resonance forms possible in the intermediate, greater charge delocalization

Question 9

what are some C3 substitution that pyridine undergoes?

Answer 9

Question 10

why is N substitution for pyridine preferred and what are some reactions?

Answer 10

Question 11

why is pyridine reluctant to undergo electrophilic aromatic substitution?

Answer 11

Question 12

on which carbon does pyridine prefer doing electrophilic aromatic substitution?

Answer 12

C3
more resonance forms, greater charge delocalisation
be able to draw the resonance structures:

Question 13

how do we carry out reactions at C4 for pyridine?

Answer 13

first prepare a Py N oxide by reacing with H2O2 then add the desired nucleophile
reduce it back to the ring
you get some C2-nitro derivatives, but that one is less favored because of sterics and electrostatic repulsion between N+ and NO2+

Question 14

How is the C4 NO2 pyridine reduced with trimethyl phosphite?

Answer 14

trimethyl phosphite is a reducing agent

Question 15

how do nucleophilic aromatic substitutions on pyridine happen?

Answer 15

they are quite easy

Question 16

how do you make synthetically useful 2-chloropyridine?

Answer 16

Question 17

why does making 2-chloropyridine only happen at C2 and not at C4?

Answer 17

Question 18

how can a benzene be added to C2 of a pyridine?

Answer 18

need a strong nucleophile, an organolithium reagent
hydride leaves because the driving force is the regeneration of the aromaticity

Question 19

how can a hydroxyl group be added to the C2 of a pyridine?

Answer 19

need a strong nucleophile, in this case OH-
you get both the keto and enol form

Question 20

what is the canizzaro reaction?

Answer 20

example of a reaction where hydride is the leaving group
this is a green chemistry reaction, no solvent is needed
-> mechanochemistry

Question 21

how do nucleophilic aromatic substitutions on Py oxide happen?

Answer 21

also happen easily

Question 22

what is the synthesis of nifluminic acid from nicotine and its function?

Answer 22

nifluminic acid=treats joint and muscle pain
use N2Cr2O7 as an oxidizing agent

Question 23

what are some natural and synthetic pyridine derivatives?

Answer 23

Question 24

what is S-lactate oxidized to and what is NAD+ reduced to, draw the reaction for this?

Answer 24

Question 25

what is pyruvate reduced to and what is NADH oxidized to, draw the reaction for this?

Answer 25

Question 26

what is kinetic resolution?

Answer 26

faster with one stereoisomer if two stereoisomers are fed to one enzyme, only one of the isomers will react lactate dehydrogenase only take S lactate to make into pyruvate R lactate would remain the same

Question 27

henderson hasselbalch equations

Answer 27

Question 28

how do the ratios of guanidinium (GH) to guanidine(G) compare at different pHs?

Answer 28

Question 29

how is it possible to reduce ketones steroselectively?

Answer 29

possible to do that using enzymes the enzymes are alcohol dehydrogenases (ADH) of which there is a large family available NAD+/NADH are used as co-factors and aqueous ispropanol is the solvent

Question 30

how is isopropanol used as a way to regenerate NADH, since it is expensive?

Answer 30

the isopropanol, as the solvent, will be oxidized to acetone this will reduce NAD+ and regenerate NADH, which was used in the reductive reaction