Alcohols

What is the general formula for an alcohol

CnH2n+1OH

Describe structure and bonding in an alcohol molecule

Contains a hydroxyl group, hydrogen bonding between alcohol molecules means strong intermolecular forces which means high melting/boiling point

Why do alcohols have higher m.p/b.p than alkanes

Hydrogen bonding is stronger than London forces in alkanes so more energy is required

What state is an alcohol at room temperature

Liquid

Trend of m.p/b.p with increasing chain length

increases as carbon chain length increases due to strong London forces

Define the term volatile

The tendency of a substance to vaporise easily

Compare volatility of alchol vs alkane

Alcohols are less volatile than alkanes of similar chain lengths because of hydrogen bonding between alcohol molecules

Describe trend in solubility with increasing chain length

Solubility deceases as chain length increases as non polar carbon chain dominates. Smaller alcohols are highly soluble in water due to OH group forming h bonds with water

Define the term primary alcohol

OH attached to a carbon bonded to 1 other carbon

Define the term secondary alcohol

OH attached to a carbon bonded to 2 other carbons

Define the term tertiary alcohol

OH attached to a carbon bonded to 3 other carbons

General formula of an aldehyde

CnH2nO

General formula of a ketone

CnH2nO

General formula of carboxylic acid

CnH2n+1COOH

Compare properties of the 3 carbonyls

All have London forces + permanent dipole-dipole forces

Boiling/Melting point increase with chain length

Polar C=O allows hydrogen bonding with water which makes it soluble

Why are the carbonyls soluble

Because the C=O is polar which can form H bonds with water increasing solubility

Which carbonyl has the highest m.p/b.p+ solubility and why

Carboxylic acids as the extra OH allows more hydrogen bonding with water which results in higher m.p/b.p and solubility

When does hydrogen bonding occur

Only if hydrogen is covalently bonded to O,F, or N

Equations for the complete combustion of alcohol

Alcohol + oxygen = carbon dioxide and water

What is the name of the reaction when alcohol undergoes combustion

Exothermic combustion

Lower alcohols burn with almost invisible flame what does this indicate

Release less energy per mole and low soot formation

How is ethanol produced

Fermentation of sugars making it a renewable biofuel

Pros and cons of using ethanol as a biofuel

Pros: renewable, reduces fossil fuel waste

Cons: lower energy density than petrol, uses farmland

What is oxidation in organic Chemistry

Addition of oxygen or loss of hydrogen

What is reduction in organic chemistry

Addition of hydrogen or loss of oxygen

When does oxidation occur in organic chem

When carbon forms a bond with a more electronegative element O,N,,F

What is the required reagents for oxidation of alcohol

Acidified potassium dichromate or H2SO4

What is the observation upon adding K2Cr2O7 for the presence of primary/secondary alcohol

Colour chnage from orange to green

What is the required conditions for partial oxidation of a primary alcohol and the product it forms

Distillation producing aldehyde

What is the required condition and product formed upon complete oxidation

Reflux producing carboxylic acid

What does secondary alcohol produce under which conditions

Reflux to produce ketone

How would you extract/collect a ketone

Distillation

Reagents to confirm the presence of an aldehyde

Tollens reagents- forms a silver mirror

Fehlings/benedicts- blue to red precipitate

What is the test for carboxylic acid

Reaction with metal carbonate producing CO2 bubbles or effervescence

What type of reaction is dehydration of alcohols

Elimination

What are the products when an alchol gets dehydrated

Alkene and water

What conditions are required for dehydration of alcohols

Heat and concentrated H2SO4 or H3PO4

What is removed during an elimination reaction kf an alchol

OH group and a hydrogen atom adjacent to it

Why can multiple products be formed from secondary and tertiary alcohols

Because there is more than one adjacent carbon so different hydrogens can be removed which results in isomers

What type of reaction forms halo alkenes from alcohols

Nucleophilic Substitution

What happens to the OH group in the substitution reaction

It is replaced by a halogen atom

Which reagent are uses to convert alcohols to haloalkane

Soduim halide and H2SO4 or Al2O3

What is the role of sulfuric acid in the substitution reaction

Provides acidic conditions in order to form hydrogen halide

What products are formed in substitution of alcohols

Haloalkane, water and a salt

How do you directly convert an alcohol to a haloalkane

Use PX3

Which carbocation is the most stable amd why

Secondary because it’s bonded to more carbons and reacts faster

Propan-1-ol is oxidised under reflux.

Which of the following statements is correct?

A. Abung must be used at the top of the condenser to ensure that no product is lost.

B. Water must flow in at the top of the condenser and out at the bottom of the condenser.

C. There must be small glass beads in the round-bottomed flask to allow the reaction mixture to boil more vigorously

D. Adding sodium hydrogencarbonate will allow the product to be distinguished from the reactants.

D

• The product is an acid

• Sodium hydrogencarbonate reacts with acids to release CO₂ gas, distinguishing the product

Explain how hydrogen bonding arises between molecules of propan-1-ol.

In your answer, you should refer to relevant partial charges and lone pairs.

• Oxygen is more electronegative than hydrogen, creating a polar O-H bond with partial charges

• There are lone pairs of electrons on the oxygen atom

• A hydrogen bond is an attraction between a lone pair on the oxygen atom of one molecule and the + hydrogen atom of a neighbouring molecule

Explain how you would collect ethanol whwn fermentation occurs name the process

Fractional distillation. Turn on the water and heat the round bottom flask. Keep the temperature below or at the boiling point of ethanol. Ethanol (and small amounts of water) vapours are formed. Ethanol vapour passes into the condenser Which cools the vapour and condenses the ethanol back into a liquid.