Organic Bases

Question 1

What is inorganic bases

Answer 1

Most don’t have a C in them

Question 2

What is organic base

Answer 2

Neutral

made up of covalent bonds

lone pair that are avaliable to react with an acid

N is most common

Question 3

Amines

Answer 3

Weak bases

Question 4

What do e- donating groups do

Answer 4

Stabilise conj base

Question 5

E- donating group and e- withdrawing group

Answer 5

Donating - increase basicity
Withdrawing - decrease basicity

(Opposite to acids)

Question 6

How do we quantify the strength of a base

Answer 6

by the strength of its conj acid. So we have to flip the reaction so it goes product -> reactant

Weaker the conj acid the stronger the base

Question 7

what is the +I effect?

Answer 7

inductive effect

donation of e- from substituent

Question 8

amines and the +I effect

Answer 8

going fromprimary to secondary amines the pKa increases and then drops down to tertiary

as the alcohol group increases the +I effect is bigger

Question 9

hydrogen bonding VS the +I effect

Answer 9

water gives a stabilising effect and the conj acids of amines can also be stabilised by H bonding

Question 10

how does this effect 1,2 and 3 amines in their roder of increasing base strength?

Answer 10

3 -> 1 -> 2

3 has 1xH and 3xOH = not as stable
1 has 3xH and 1xOH = little less stable
2 has 2xH and 2x OH = most basic

Question 11

weakest not basic organic base?

Answer 11

pyrrole
- lowest pKa -3.8

Question 12

weakly basic organic bases?

Answer 12

aniline and pyridine with low pKas

Question 13

strongest organic base?

Answer 13

guanidine

Question 14

pKa of guanidine

Answer 14

13

Question 15

how is the nitrogen basicity inreased in guanidien?

Answer 15

by the +M effect from the 2 other N lone pairs

Question 16

which N is protonated in guanidine

Answer 16

N on top of the = bond

Question 17

how does guanidine get protonated?

Answer 17

1. one pair move from N to the middle C
2. arrow from double bond to N

neutralises the + charge by putting e- onto it

Question 18

what does the +M effect stabilise?

Answer 18

the conj acid of guanidine

Question 19

amide pKa?

Answer 19

-1

Question 20

are amine N basic?

Answer 20

no

Question 21

what is +M effect

Answer 21

gives a negative charge to the conjugate system

an electron-donating group that ‘pushes’ electrons onto the carbon atom it is bonded to, usually via a lone pair

Question 22

pyrrole pKa

Answer 22

-3.8

Question 23

what is the N in pyrrole

Answer 23

lone pair are part of stable pi system

N is sp2 hybridised with the lone pair occupying the p orbital

Question 24

lone pair on N of a pyridine

Answer 24

not part of pi system and so are available to react with an acid

The N is sp2 and the lone pair are in a sp2 orbital and protonation occurs via these

Question 25

The more S character an orbital has …..

Answer 25

The more tightly it it holds onto its e- and so the more e- withdrawing it is. This is inductive not conjugation

Question 26

Lone pair on alinines

Answer 26

Partially conjugated (orbital at 40degrees) with the e- withdrawing aromatic pi system and therefore less availiable to react with an acid

Question 27

What is the most basic N in imadazole? pyrolysis or pyridine

Answer 27

N1 which is the pyrrole with N-H