1. Biological Chemistry FIRST YEAR ORGANIC CHEMISTRY
Lecture Six
Alcohols and Ethers
Convenor : Dr. Fawaz Aldabbagh

2. Alcohols and Ethers
Alcohols and Ethers can be regarded as derivatives of water in which one or two of the H atoms has been replaced by an alkyl group
Saturated molecules are sp3 hybridized
Electronegativity of oxygen causes an unsymmetrical distribution of charge

3. Alcohols are found to have much higher bpt than those of alkanes or haloalkanes of comparable size, e.g. Methanol (65 oC), Chloromethane and Methane are gases ; Ethanol (78.5 oC), Chloroethane (12 oC) and Ethane is a gas
Methanol and Ethanol are classed as Polar Molecules (Hydrophilic) – They are Infinitely Soluble in Water
Why? Answer – Hydrogen Bonding
H-bonds weaker than covalent bonds, although these bonds can be continually broken and reformed – a highly ordered structure results – H-Bonding to water can also occur
Water (mw = 18) is a liquid, bpt 100oC – otherwise a gas

4. Solvent in varnishes, paint
As R-group increases in size, so does the solubility in non-polar solvents
As the number –OHs increases so does solubility in water
Bpt increase with chain length and number of –OHs
Methanol, CH3OH
Solvent in varnishes, paint
Racing Car Fuel (easy to put out flames)
Highly Toxic – “Blindness” - Formaldehyde
Ethanol, CH3OH
Drinking Alcohol
50% Ethanol is flammable

5. Preparation of Ethanol
Ethanol content; Beer, 3-9% ; Wine, 11-13% ; Whisky, 40-45% ; Vanilla Extracts, 35% ; Night Nurse, 25% ; Listerine, 25%
Preparation of Ethanol
- Fermentation of Sugar – Break down of sugar to CO2 and Ethanol by Yeast Enzymes
- Industrial Process – Hydration of Ethene
Naming Alcohols
Methyl alcohol
(methanol)
Ethyl alcohol (ethanol)
Propyl alcohol (propanol)
Isopropyl alcohol
2-Ethyl-1-butanol

6. Naming Alcohols Harmless Extremely Toxic
Polyhydroxy alcohols are alcohols that possess more than one hydroxyl group
1,2,3-Propanetriol (glycerol)
1,2-Propanediol (propylene glycol)
1,2-Ethanediol (ethylene glycol)
Harmless
Extremely Toxic
Calcium Oxalate crystallises in the kidney leading to renal problems

7. Alcohols are weak Acids
pKa CH3OH (15.5), H2O (15.74), CH3CH2OH (15.9), (CH3)3COH (18.0)
The Conjugate base of an alcohol is an alkoxide ion
Because most alcohols are weaker acids than water ; they’re respective alkoxide is a stronger base than hydroxide ion OH -

8. -OH is a Poor Leaving Group
Sodium Ethoxide
-OH is a Poor Leaving Group
Weak acids make Poor Leaving Groups in Organic Reactions
Strong Acids have Conjugate Bases that are Good Leaving Groups in Organic Reactions
We have to convert OH into a Good Leaving Group

9. OMs and OTs are excellent leaving groups in Nucleophilic
Substitution Reactions- Derivatives of Sulfuric Acid

10. SN2 – Substitution, Nucleophilic, Bimolecular
Other Good Leaving Groups ;
R-I > R-Br > R-Cl > R-F It follows Acid Strength
HI > HBr > HCl > HF
SN2 – Substitution, Nucleophilic, Bimolecular
Backside Nucleophilic Attack – Inversion in Configuration
Optically Active
Enantiomericaly Pure
Concerted Mechanism

11. SN1 – Substitution, Nucleophilic, Unimolecular
                               
Professor George Olah
Nobel Prize 1994
Carbocation is sp2-planar

12. Evidence for SN1 is Racemization of an optically active compound
The Carbocation intermediate is attacked by water from either side by the same rate
Phenols
Much high bpt, because of H-Bonding
(e.g. Phenol, 182C, toluene, 111C
1-Naphthol
2-Naphthol
Phenol
4-Methylphenol

13. Phenols are much stronger acids than alcohols

14. ETHERS, RO-OR Cyclic Ethers Non-Flammable Anaesthetics
1-Propoxypropane
Methoxycyclohexane
Methoxybenzene
Bpt are similar to alkanes – No H-bonding to one another
But are soluble in water- H-bonding to water - Polar
Flammable – Ether can cause flash fires
Low Reactivity – Make Good Reaction Solvents
Cyclic Ethers