Organic acids and bases Flashcards
In the Bronstead-Lowry theory, what are acids and bases
Acids are defined as proton donors
Bases are defined as proton acceptors
In Bronstead-Lowry terms, what is an acid-base reaction?
A reactions occurs when an acid transfers a proton to a base
What is a conjugate base
Is the chemical compound formed by the donatation of a proton from a Bronstead acid
What is a conjugate acid
is the chemical compound formed by the reception of a proton by a Bronstead base
The strength of an acid is the extend of the dissociation of an acid (HA) in solution
Describe the equation for this and the associated acid dissociation constant
How can interconvert between pKa to Ka
The lower the pKa…
the stronger the acid
This is due to the negative sign of the pKa equation
The stregth of an acid depends on two key factors, what are they?
- The strength on the HA bond (the weaker the HA bond is, the stonger the acid)
- The stability of the conjugate base (the more stable the conjugated base, the stronger the acid)
Within the same period (row), what happens to the acidity of an organic compound as the electronegativity of a consitituent increases
Acidity increases
e.g. methanol is more acidic than methylamine
Down a group, electronegativity decreases, what happens to the strength of an acid
The strength of an acid increases
Due to the weakening bond strength on descending the group, which means the stability of the anion increases as the charge can be spread over a larger atom
What happens to acidity, when the charge on the conjugate base can be delocalised over two or more atoms through resonance forms
acidity increases
e.g. ethanoic acid is a much stronger acid than methanol. The negative charge can delocalise between both oxygen atoms in the conjugate base of ethanoic acid
Known as the resonance effect
What happens to the strength of an acid if electron withdrawing groups are added
The negative charge can be spread with the electron-withdrawing groups, which will stabilise the conjugate base and therefore the strength of the acid
Known as the inductive effect
The inductive effect decreases with distance
What two factors will influence the strength of a conjugate base - hence an acid
Resonance effects
Electronegativity and inductive effects
When considering the inductive effect, would a methyl group or tert-butyl groups be more electron donating
The tert-butyl would be more electron donating - increasing the stability of the conjugate base (because it is anionic and not a cation) and hence the strength of the acid
They release of electrons is through a process called
hyperconjugation
If an base has a high pKaH this means
AH⁺ is a poor acid, the equilibrium is over to the left
Hence A must be a strong base
