9 - HETEROCYCLES Flashcards

1
Q

why is pyridine a weaker base than piperidine?

A
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1
Q

what are some natural and synthetic derivates of pyridine?

A
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2
Q

how do orbitals affect acidity and basicity?

A
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3
Q

how does electronegativity play a role in acidity/basicity?

A
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4
Q

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

A
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5
Q

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

A
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6
Q

how is dihydropyridine reduced to aromatic pyridine by DDQ?

A
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7
Q

what is the mechanism of the Hantzsch pyridine synthesis?

A
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8
Q

which carbon substitution does pyridine prefer?

A

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

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9
Q

what are some C3 substitution that pyridine undergoes?

A
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10
Q

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

A
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11
Q

why is pyridine reluctant to undergo electrophilic aromatic substitution?

A
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12
Q

on which carbon does pyridine prefer doing electrophilic aromatic substitution?

A

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

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13
Q

how do we carry out reactions at C4 for pyridine?

A

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+

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14
Q

How is the C4 NO2 pyridine reduced with trimethyl phosphite?

A

trimethyl phosphite is a reducing agent

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15
Q

how do nucleophilic aromatic substitutions on pyridine happen?

A

they are quite easy

16
Q

how do you make synthetically useful 2-chloropyridine?

A
17
Q

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

A
18
Q

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

A

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

19
Q

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

A

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

20
Q

what is the canizzaro reaction?

A

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

21
Q

how do nucleophilic aromatic substitutions on Py oxide happen?

A

also happen easily

22
Q

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

A

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

23
Q

what are some natural and synthetic pyridine derivatives?

A
24
Q

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

A
25
Q

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

A
26
Q

what is kinetic resolution?

A

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

27
Q

henderson hasselbalch equations

A
28
Q

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

A
29
Q

how is it possible to reduce ketones steroselectively?

A

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

30
Q

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

A

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