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Flashcards in Heterocyles - directing effect Deck (14)
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1
Q

what is a heterocyclic compound?

A

a cyclic compound in which one or more of the ring atoms is an atom other than carbon

2
Q

why is the carbon substituted atom of a 6-membered heteroaromatic system in a trigonal planar?

A

to keep the hexagonal ring flat

3
Q

where does the 5 delocalised electrons in the 6-membered heteroaromatic system stay?

A

in the P orbital

4
Q

which is the weaker base, pyridine or piperidine?

A

pyridine

5
Q

which is more stable and why, pyridine or piperidine?

A

pyridine due to its aromaticity-so the C=C bonds cause resonance increasing stability.

6
Q

does the lone pair of electrons on nitrogen in a heteroaromatic structure interact with the pi cloud?

A

no the lone pair is in a plane of its own

7
Q

what is pyridine used as in a nucleophilic substitution reaction with acyl chloride?

A

it acts as a nucleophile to help make an ester from the acyl chloride

8
Q

what does the nitrogen atom in a heteroaromatic structure do to the rest of the ring?

A

it reduces the energy of all the orbitals making the ring a less reactive nucleophile and a more reactive electrophile as the nitrogen destabilises the cationic intermediate that would form in a nucleophilic reaction

9
Q

explain how pyridines are made in the Hantzsch pyridine synthesis mechanism?

A
  1. aldehyde and keto-ester react in an aldol reaction
  2. addition of keto-ester to the enone, then add ammonia causing cyclisation
  3. oxidation to pyridine
10
Q

what is the most common chemical reaction heterocycles with >2 nitrogen atoms undergo?

A

nucleophilic substitution

11
Q

which mechanism is more common in pyrrole’s, nucleophilic or electrophilic substitution?

A

electrophilic substitution

12
Q

what is the big difference between pyrrole and pyridine?

A

the nitrogen lone pair is delocalised around the ring in a pyrrole but in a pyridine it’s in a plane of its own and doesn’t interact with the delocalised electrons.

13
Q

what is formed when you replace a carbon atom in a 5 membered heterocycle with a nitrogen atom at the 3 position?

A

an imidazole

14
Q

which is more basic and acidic pyrroles or imidazole?

A

imidazole

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