hybridisation etc

What do sp³ orbitals look like?

Explain sp³ hybridisation

Carbon forms 4 single bonds

Each valence electron has ¼ s-orbital character and ¾ p-orbital

Each orbital is sp³ hybridised

sp³ MO diagram

Explain sp² hybridisation

Carbon is bonded to 3 atoms (double bond)

Three orbitals are hybridised to have 1/3 s-orbital character and 2/3 p-orbital

Each orbital is sp² hybridised

What happens to the remaining p-orbital in sp² hybridisation?

It forms a π-bond with a p-orbital from another atom

sp² MO diagram

Explain sp hybridisation

C is bonded to 2 atoms (triple bond)

Two orbitals are hybridised; ½ s-orbital and ½ p-orbital character

sp hybridisation diagram

What does HOMO and LUMO stand for?

HOMO = highest occupied molecular orbital

LUMO = lowest unoccupied molecular orbital

What are inductive effects (±I)

Electron withdrawing (-I) effects and electron donating (+I) effects

• electronegativity creating polar bonds

How to increase stability of carbocation intermediates? (inductive)

More +I (electron donating) groups increases stability

How to increase stability of carbocation intermediates? (alkyl groups)

They have an empty p-orbital

Having more alkyl groups through hyperconjugation

• stabilise the charge

What is conjugation?

π-electrons on adjacent bonds can delocalise their electrons across the π-system

Why are conjugated systems flat?

Orbital overlap is most effective when the p-orbitals are parallel.

What happens as you increase the number of double bonds?

The HOMO-LUMO gap gets smaller

• absorb light in the visible region

What are mesomeric (±M) effects?

The movement of electron density within the π system of the molecule by resonance conjugation

-M is electron withdrawing

+M is electron donating

Diagrams of -M (electron withdrawing) effects

Where are electrons moving to/from?

From p-orbital to empty π* orbital

Diagrams of +M (electron donating) effects

How do the orbitals overlap in -M (electron withdrawing) C=O with heteroatoms?

The π* orbital overlaps with lone pairs in p-orbitals of heteroatoms

What is pKa in terms of pH?

The pH at which the acid is half-dissociated

What does a high/low pKa mean?

• basic/acidic?

high pKa is strong base

low (negative) pKa is weak base

How does equilibrium shift when two molecules are together in solution?

Equilibrium shifts towards the most stable conjugate base (lowest pKa)

Which way would equilibrium be favoured?

What pKa value do you need when deprotonating a molecule?

Use a base with a higher pKa value

How do orbitals overlap when forming a bond?

HOMO of one molecule overlaps with LUMO of another