4.3 - Alcohols and haloalkanes Flashcards
What are alcohols ?
They are a homologous series with the functional group -OH ( hydroxyl group )
How do you name alcohols ?
- Name ends in -ol/ starts with hydroxy-
- Count from end nearest -OH unless C=C present ( then count from end nearest of double bond )
What are the physical properties of alcohols in comparison to Alkanes ( of the same chain length ) ?
- Less volatile
- High melting points
- Greater water solubility
Explain why alcohols have a higher melting point than alkanes ( of the same chain length ) ?
- Alkanes have non-polar bonds because the electronegativity of hydrogen and carbon are very similar
- Alkanes are therefore non-polar
- Therefore there are only weak London forces between alkane molecules which don’t require a lot of energy to overcome
- Alcohols have a polar O—H bond because of the difference in electronegativity of the oxygen and hydrogen atoms
- Alcohols are therefore polar
- Therefore, the are weak London forces and strong hydrogen bonds between molecules which require more energy to overcome resulting in higher boiling point
Explain why alcohols are less volatile than alkanes ( of the same chain length ) ?
- More energy is required to overcome strong hydrogen bonds and weak London forces between alcohol molecules than to overcome only weak London forces between alkane molecules
- Therefore, alcohols are less volatile than alkanes
Explain why alcohols are more water soluble than alkanes ( of the same chain length ) ?
- Alkanes are non-polar molecules and cannot form hydrogen bonds with water
- Alcohols are polar molecules that can form hydrogen bonds with water between the polar -OH group and water molecule
- Therefore they are more water soluble than alkanes
Explain the effect of size on water solubility of alcohols?
- As the size of the alcohol increases, the size of the R group on the alcohol increases
- A long-chain alcohol can only form hydrogen bonds between the polar -OH group and water molecule, the rest of the molecule is non-polar and cannot form hydrogen bonds with water between
- As the hydrocarbon chain increases in size, the influence of the -OH group becomes relatively smaller, and the solubility descreases
Draw a diagram showing formation of hydrogen bonds between alcohol molecules ?
Draw a diagram showing hydrogen bonds forming between alcohol and water molecules ?
What are the different types of alcohols ?
- Primary alcohols
- Secondary alcohols
- Tertiary alcohols
Draw the structure of a primary, secondary and tertiary alcohol ?
What are the different reactions with alcohols ?
- Combustion of alcohols
- Oxidation of alcohols
- Dehydration of alcohols
- Substitution reactions
What are the features of the combustion of alcohols ?
- Alcohols undergo complete combustion in a plentiful supply of Ov2, forming COv2 and Hv2O
- The reaction is exothermic
- As the number of carbons in the alcohol molecule increases, the amount of energy that is released per mole increases
Write an equation to show ethanol undergoing complete combustion ?
Cv2Hv5OH + 3Ov2 —> 2COv2 + 3Hv2O
Do you know how to write and balance equations showing combustion of alcohols ?
Yes
How is an oxidising agent written in an equation showing the oxidation of alcohols ?
The symbol [O] is used to symbolise an oxidising agent
What are the different oxidations of alcohols ?
- Oxidation of primary alcohols to from aldehydes
- Oxidation of primary alcohols to form carboxylic acids
- Oxidation of secondary alcohols to form ketons
State the reagents, conditions and observations for the oxidation of primary alcohols to form aldehydes ?
- Reagents : Primary alcohol, acidified potassium dichromate (VI) [ Kv2Crv2Ov7 / H+ ]
- Conditions : Distillation
- Observations : Solution goes from orange to green
Write an equation to show the oxidation of primary alcohol to form aldehydes ( ethanol ) ?
State the reagents, conditions and observations for the oxidation of primary alcohols to form carboxylic acids ?
- Reagents : Primary alcohol, acidified potassium dichromate (VI) [ Kv2Crv2Ov7 / H+ ]
- Conditions : Reflux
- Observations : Solution goes from orange to green
Write an equation to show the oxidation of primary alcohol to form carboxylic acids ( ethanol ) ?
State the reagents, conditions and observations for the oxidation of secondary alcohols to form ketones ?
- Reagents : Secondary alcohol, acidified potassium dichromate (VI) [ Kv2Crv2Ov7 / H+ ]
- Conditions : Reflux
- Observations : Solution goes from orange to green
Write an equation to show the oxidation of secondary alcohols to form ketones ( propane-2-ol ) ?
Explain why tertiary alcohols cannot be oxidised / no reaction occurs ?
A strong carbon-carbon bond would have to be broken in order to oxidise a tertiary alcohol
Write an equation to show the oxidation of a tertiary alcohol ( 2-methylpropan-2-ol ) ?
Draw the apparatus setup for a distillation and label ?
Draw the apparatus setup for a reflux and label ?
State the reagents, conditions, products formed and type of reaction for the dehydration of alcohols ?
- Reagents : Alcohol
- Conditions : Reflux, concentrated Hv2SOv4 ( sulphuric acid ) or Hv3POv4 ( phosphoric acid ) catalyst
- Product formed : Alkene + water
- Type of reaction : Elimination reaction
Write an equation to show the dehydration of alcohols ( propane-2-ol ) ?
State the reagents, conditions, products formed and type of reaction for the substitution reactions of alcohols ?
- Reagents : Alcohol, Hv2SOv4, NaBr ( or KBr, NaCl, KCl )
- Conditions : Reflux
- Product formed : Haloalkane + water + NaHSOv4/KHSOv4
- Type of reaction : Substitution reaction
Write an equation to show the substitution reactions of alcohols ( Ethanol + sodium bromide ) ?
Explain why this alcohol cannot be dehydrated ?
It cannot be dehydrated as there is no hydrogen atom bonded to the adjacent carbon of the alcohol
What is an electrophile ?
An electron pair acceptor
What is a nucleophile ?
An electron pair donor
What happens when a nucleophile attacks a haloalkane ?
- A substation reaction takes place where the halogen atom is replaced by the nucleophile
- The mechanism for this type of reaction is nucleophilic substitution
Name the mechanism, regents, conditions and nucleophile in hydrolysis of haloalkanes ?
- Nucleophilic substitution
- Reagents : haloalkane + NaOH/KOH ( aq )
- Conditions: Reflux, aqueous ethanol solvent
- Nucleophile : OH-
Can you draw the mechanism for nucleophilic addition ( bromomethane ) ?
Can you write the full and ionic equation for nucleophilic addition ( bromomethane ) ?
What does the rate of hydrolysis of primary haloalkanes depend on ( in term of bond enthalpies ) ?
- The rate of hydrolysis depends on the strength of the carbon-halogen bond
- The stronger the carbon-halogen bond ( the greater the bond enthalpy ), the slower the reaction
What are organohalogens ?
- Molecules containing at least one halogen atom joined to a carbon chain
- They are mostly synthetic so not broken down easily and cause of environmental concern
What are the uses of organohalogens ?
- general solvents
- Dry-cleaning solvents
- Making polymers
- Flame retardants
- Refrigerants
What is the ozone layer ?
- The ozone layer is found at the outer edge of the stratosphere
- A small proportion of the gases in the stratosphere are ozone, Ov3
- Ozone absorbs UV-B radiation
Write the equation for how ozone is formed ?
What are CFC’s and HCFC’s ?
CFC = chlorofluorocarbon
HCFC = hydrogen - chlorofluorocarbon
What are the effects of CFC’s and HCFC’s on the ozone layer ?
CFC’s stay stable until they reach the stratosphere, where they absorb UV light, which breaks the strong carbon-chlorine bonds, forming reactive chlorine radicals
Write the imitation and propagation mechanisms for the effect of CFC’s and HCFC’s on the ozone layer ( CFv2Cl ) ?
What are other radicals that also cause ozone depletion ?
NO* radicals formed when aircraft travel in the stratosphere ( and during lighting strikes ) can also breakdown ozone
Write the imitation and propagation mechanisms for the effect of other radicals on the ozone layer ?
What are replacements for CFC’s ?
- Aerosols : butane is used
- Flame retardants : brominated molecules are used ( but may be toxic )
