1. Orbitals – s, p – different shapes Valence Bond model – hybridisation,  and  bonds Conjugation (14.1) Alternate  bonds Hyperconjugation (6.6)  bonds & C-H bonds Aromaticity (15.3) Alternate  bonds and 4n+2 electrons Electronegativity (2.1) Inductive effects Resonance (2.5,2.6) Stability if more forms Molecules with  bonds Ways of explaining stability of organic molecules Molecules with  bonds

2. 2 Polar Covalent Bonds: Electronegativity Covalent bonds can have ionic character These are polar covalent bonds – Bonding electrons attracted more strongly by one atom than by the other – Electron distribution between atoms is not symmetrical Inductive effect: shifting of electrons in a bond in response to EN of nearby atoms

3. 3 Acids and Bases: The Brønsted– Lowry Definition A Brønsted acid is a substance that donates a hydrogen ion (H + ) A Brønsted base is a substance that accepts the H + – “proton” is a synonym for H +

4. 4 K a – the Acidity Constant K a ranges from 10 15 for the strongest acids to very small values (10 -60 ) for the weakest pK a = -log K a A smaller value of pK a indicates a stronger acid and is proportional to the energy difference between products and reactants

5. 5 If A- (RHS) is more stable – then HA is strong acid How can A- be stabilised relative to HA? 1.Negative charge must end up on electronegative atom Electronegative – likes electrons (negative charge)  Usually O-H more acidic than N-H > C-H – carboxylic acid, alcohol more acidic than acetone) How to predict if a compound will be a strong/weak acid?

6. 6 If A- (RHS) is more stable – then HA is strong acid How can A- be stabilised relative to HA? 2.Inductive effects Other electronegative atoms – draw negative charge away, spread out  Compounds with CF3 more acidic than CH3 page 604, chapter 17 – section 17.2 - alcohols page 759, chapter 20 - section 20.4 – carboxylic acids

7. 7 If A- (RHS) is more stable – then HA is strong acid How can A- be stabilised relative to HA? 3.A- has many ‘good’ resonance forms relative to HA Many resonance forms – spread/delocalisation of negative charge  eg COOH compared with COH, or alkyl-OH and phenol Alkyl alcohol vs phenol Section 17.2, page 605-606 Carboxylic acid vs alcohol Section 20.2 page 757 How many resonance forms can be drawn? How many resonance forms can be drawn?

8. 8 If A- (RHS) is more stable – then HA is strong acid How can A- be stabilised relative to HA? (less common factors) 4.A- has aromatic character, HA does not HA not aromatic, but A- aromatic – e.g. cyclopentadiene  see page 526 - chapter 15, section 15.4 Cyclopentadiene gives away H+ so that it can achieve aromatic stability Cyclooctatriene?

9. 9 If A- (RHS) is more stable – then HA is strong acid How can A- be stabilised? (less common factors) 5.A- - negative charge ends up on orbitals with more s character (e.g. sp) Alkynes more acidic than alkenes>alkanes  page 271 – chapter 8, section 8.7 – read up yourself How about dibasic acids? How about bases?