Organic Bases Flashcards
What is inorganic bases
Most don’t have a C in them
What is organic base
Neutral
made up of covalent bonds
lone pair that are avaliable to react with an acid
N is most common
Amines
Weak bases
What do e- donating groups do
Stabilise conj base
E- donating group and e- withdrawing group
Donating - increase basicity
Withdrawing - decrease basicity
(Opposite to acids)
How do we quantify the strength of a base
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
what is the +I effect?
inductive effect
donation of e- from substituent
amines and the +I effect
going fromprimary to secondary amines the pKa increases and then drops down to tertiary
as the alcohol group increases the +I effect is bigger
hydrogen bonding VS the +I effect
water gives a stabilising effect and the conj acids of amines can also be stabilised by H bonding
how does this effect 1,2 and 3 amines in their roder of increasing base strength?
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
weakest not basic organic base?
pyrrole
- lowest pKa -3.8
weakly basic organic bases?
aniline and pyridine with low pKas
strongest organic base?
guanidine
pKa of guanidine
13
how is the nitrogen basicity inreased in guanidien?
by the +M effect from the 2 other N lone pairs
which N is protonated in guanidine
N on top of the = bond
how does guanidine get protonated?
- one pair move from N to the middle C
- arrow from double bond to N
neutralises the + charge by putting e- onto it
what does the +M effect stabilise?
the conj acid of guanidine
amide pKa?
-1
are amine N basic?
no
what is +M effect
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
pyrrole pKa
-3.8
what is the N in pyrrole
lone pair are part of stable pi system
N is sp2 hybridised with the lone pair occupying the p orbital
lone pair on N of a pyridine
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
The more S character an orbital has …..
The more tightly it it holds onto its e- and so the more e- withdrawing it is. This is inductive not conjugation
Lone pair on alinines
Partially conjugated (orbital at 40degrees) with the e- withdrawing aromatic pi system and therefore less availiable to react with an acid
What is the most basic N in imadazole? pyrolysis or pyridine
N1 which is the pyrrole with N-H
