Fluorenone/Aldol - Post-Lab

Catalytic Hydrogenation

Chemical reaction where H2 adds across a C-C double bond in presence of a transition-metal catalyst (Ex.: Ni, H2)

Hydride Reducing Agent

Donates H- to an electrophile; LiAlH4 and NaBH4.

Racemic Mixture

A mixture with equal amounts of two enantiomers

Asymmetric Synthesis

Selective synthesis of a single enantiomer of a chiral compound

Hydride Reducing Agent Strength - Metal EN Difference

The more EN it is, the stronger it pulls its e-; less likely to give up H+.

Hydride Reducing Agent Strength - Valence Shell e- Configuration

Determines EN, orbital size, and ability to stabilize a positive charge after losing the hydride ion.

Hydride Reducing Agent Strength - Solvent Issues

You must use a aprotic solvent to prevent formation of H2.

Disadvantages and Advantage of using NaBH4

- Much safer to handle as it is more EN

- Will react with protic solvents readily and is less reactive.

General Mechanism of Reduction

1. Carbonyl C takes H from NaBH4, creating a negative charge on the O that attracts Na+

2. The negative O attacks the B and makes it negatively charged

3. Repeated 3 more times

4. Addition of H+/H20 to make secondary alcohol.

IR Analysis of Reduction

Alcohol peak with BIG C-H/C-C area

Percent Yield Analysis - Reduction

Ideal is 70% but students should get 30-50%

MP Analysis - Reduction

153-154 C

alpha-Hydrogen/Proton

Hydrogen located on the C next to the carbonyl C

Alpha-Carbon Enolate

Nucleophile formed when an alpha H is removed from the alpha C

Enolate

Anion formed from the deprotonation of the alpha-carbon; resonance-stabilized.

Mixed Aldol Condensation

Two different carbonyl compounds (aldehydes and ketones) react to form a C-C bond.

Why are a-protons more acidic than an alkane proton?

Removal of a-protons are resonance stabilized, while removing an alkane proton destabilized the carbanion.

Mixed Aldol Condensations - What are the problems?

- There are multiple Nu (a-protons) and multiple electrophiles. It can make 4 products that are difficult to separate.

- It has a negative Keq, which means it is reactant favored.

Mixed Aldol Condensations - How do we solve our problem?

- First, you make the enolate. Then, you add the enolate to your final solvent (carbonyl C)

- Use a strong base (LDA) to shift equilibrium in favor of the enolate

Mixed Aldol Condensations - Why we don't need to worry about the problems with our reaction?

- Only acetophenone has an alpha proton and can become the enolate.

- Steric hinderance makes aldehyde more reactive (can use NaOH)

- Quickly undergoes dehydration

General Reaction and Mechanism

1. Addition of strong base causes the formation of a C-C bond and reduction of carbonyl on aldehyde.

2. Product rapidly dehydrates and produces water.

IR Analysis - Aldol

- Presence of carbonyl peak, small little peaks close together

- Large fingerprint region

% Yield Analysis - Aldol

Ideal is 75%. Student is 30-50%.

MP Analysis - Aldol

73-78 C