Comparing acidity

Molecules are usually those with -OH and COOH groups.
Benzene:
1. The benzene group is electron withdrawing.
2. [phenol only] Lone pair on O atom is delocalised onto the ring.
3. Conjugate base produced is more stable
4. A is a stronger acid than B because A has a benzene ring.
Alkyl groups:
1. Alkyl group is electron releasing.
2. [alcohol only] Electrons are released towards the O atom.
3. The O atom attracts H+ more strongly4. A has more/longer alkyl groups attached to the C (in C-OH). Thus, electron releasing effect is stronger, making it a weaker acid.

Note: no. of alkyl groups is more important than length.
Carboxylic acids (COOH):
1. p-orbitals of C and O atoms in COOH overlap to form a delocalised system.
2. Conjugate base formed is more stable.
3. It loses H+ more easily, making it a stronger acid.
4. A is more acidic than B because it has a COOH group.
Halogens:
1. Halogen atoms are electronegative and draw electrons towards themselves.
2. Negative charge is drawn away from the O atom/COO- group.
3. Conjugate base formed is more stable.
4. It loses H+ more easily, making it a stronger acid.
5. A is more acidic than B because it has more halogen atoms/more electronegative halogen.
Priority when assessing acidity: COOH > benzene > alkyl/halogen

Comparing basicity

Molecules are usually those with amine (NH2) or amide (CONH2) groups.
Benzene:
1. The benzene group is electron withdrawing.
2. Lone pair on N atom is delocalised onto the ring.
3. N atom is less electronegative and less able to donate a lone pair to H+ ions.
4. A is a weaker base than B because it has a benzene ring.
Alkyl group:
1. Alkyl group is electron releasing.
2. Electrons are released towards the N atom.
3. N atom is more electronegative and more able to donate a lone pair to H+ ions.
4. A is a stronger base than B because it has more/longer alkyl groups.
Halogen:
1. The halogen atom is electron withdrawing.
2. Electrons are drawn away from the N atom.
3. The N atom is less electronegative and less able to donate a lone pair to H+ ions.
4. A is a weaker base than B as it has more halogen atoms/more electronegative halogens.
Amide:
1. Electrons on N atoms are delocalised because p-orbitals of C, N and O overlap.
2. Electron density on N atom decreases.
3. The N atom is less electronegative and less able to donate a lone pair to H+ ions.
4. A is a weaker base than B because it is an amide.
Amines are usually stronger bases than amides. However, when comparing different amines or amides, alkyl group > benzene/halogen