Textbook Notes (280,000)
CA (170,000)
McMaster (10,000)
CHEM (300)
Chapter 13

CHEM 2OB3 Chapter Notes - Chapter 13: Sodium Borohydride, Hydroxy Group, Phosphorus Tribromide


Department
Chemistry
Course Code
CHEM 2OB3
Professor
Paul Harrison
Chapter
13

This preview shows pages 1-2. to view the full 8 pages of the document.
13: Alcohols and Phenols
Structure and Nomenclature
1. Name the parent
-Longest chain has to include the hydroxyl
group
-2 hydroxys = “ediol” or “___ glycol”
-Cyclic alcohols: ‘phenol’ can be used as the
parent chain
2. Name the substituents
3. Assign locant to each substituent
-Hydroxy group should have the lowest
number
o3-pentanol or pentan-3-ol
-Chrial center present: R or S
-Cyclic alcohols: hydroxyl group is
understood as 1
4. Assemble the substituents alphabetically
Physical Properties
Boiling Point:
-Alcohols have a high boiling point: H
bonding
Ex. Ethanol: H bonding between OH
molecules
Miscibility:
-Not all alcohols are miscible with water
(except Methanol)
-Alcohols have hydropobic and hydrophilic
regions via H-bonding
o
the hydrophobic region (longer the
chain) =
solubility
oExcept butanol is consider soluble (certain
volume of butanol can dissolve in a specified
amount of water at room temperature) not miscible
Commercially Important Alcohols
-Methanol: heating wood in the absence of air or Co2 + H2; toxic
-Ethanol: fermentation of grains or fruits; drinking
-Isopropanol: rubbing alcohol; sterilization
Acidity
Acidity of Hydroxyl Functional Group
-Compare via conjugate base, alkoxide ion
oNegative charge on oxygen atom
-Acidity: hydrogen halides > alcohols > amines and alkanes
-
Stability =
acidity
Reagents for Deprotonating Alcohol
1. Strong base (NaH)
-H- deprotonates the alcohol to generate hydrogen gas
2. Li, Na or K
-Metals react with alcohol to liberate H2, producing alkoxide ion

Only pages 1-2 are available for preview. Some parts have been intentionally blurred.

Factors Affecting Acidity
1. Resonance
-Phenolate/Phenoxide ion: Resonance-stabilized anion
-Phenoxide ions can be deprotonated by a hydroxide ion
-
Resonance =
acidity
2. Induction
-
attachments to electroneg atoms =
acidity
3. Solvation Effects
-
steric hindrance =
acidity
-Less steric hindrance allows for stability by the solvent
Preparation of Alcohols via Substitution or Addition
Substitution
-Tertiary alcohols undergo Sn1
-Primary alcohols undergo Sn2
-Secondary alcohols: in Sn1 condiions, its too slow; in Sn2, favour elimination over substitution
Addition
Preparation of Alcohols via Reduction
Oxidation States
-Bonds are treated heterolytically (ionic bonds)
-Formal charge: 0
-Oxidation state: 2-
-Oxidation: change to a more positive charge
Reduction: change to a more negative charge
Reducing Agents (oxidize)
Ketone  Aldehyde
A. Hydrogenation occurs in presence of metal catalysts, high pressure and
high temperature
B. NaBH4 is used as a reducing agent
-Source of H- and the
solvent functions as H+
(ex. Methanol, ethanol or
water)
You're Reading a Preview

Unlock to view full version

Only pages 1-2 are available for preview. Some parts have been intentionally blurred.

C. LAH (or LiAlH4) is also a
reducing agent, similar to
NaBH4
-delivers H- and reats
violently with water,
so a protic solvent
cannot be present
with LAH
-Ketone or aldehyde
is treated with LAH
and in a separate step, the proton source (H2O or
H3O+) is added to the flask
*Must be two separate steps
-Treated with hydride reducing agent, carbonyl group is
reduced
-Catalytic hydrogenation reduces the C==C bond
-Thus, hydride reducing agents > catalytic hydrogenation
-LAH is more reactive than NaBH4
-LAH is less selective
-LAH will react with carboxylic acid or ester  alcohol
Preparation of DIols
You're Reading a Preview

Unlock to view full version