Unit 3.4.5 - Carbonyl groups Flashcards
What functional group do aldehydes and ketones share?
=O
What is the difference between aldehydes and ketones?
Aldehydes have the =O at the end of the carbon chain Ketones have the =O in the middle of the carbon chain
How can aldehydes be made?
By oxidising primary alcohols
How can ketones be made?
By oxidising secondary alcohols
What suffix is used to name aldehydes?
-al
What suffix is used to name ketones?
-one
Other than the suffix used what is the difference between naming aldehydes and ketones?
With ketones you have to say the number of the carbon the functional group comes off
What can you oxidise an aldehyde too?
Carboxylic acid
What can you oxidise a ketone too?
It can’t be oxidised
Name three tests to distinguish between aldehydes and ketones.
You heat with …… Tollen’s reagent, Benedict’s solution or Fehling’s solution
What do all the tests for distinguishing between aldehydes and ketones work on?
The fact an aldehyde can be oxidised but a ketone can’t
What is Tollen’s reagent?
Colourless solution of silver nitrate dissolved in aqueous ammonia
What are the results when a ketone and aldehyde is mixed with Tollen’s reagent?
Ketone - no visible change Aldehyde - silver mirror forms
What is the equation for when diamine silver ions are reduced, when they are used as Tollen’s reagent?
[Ag(NH₃)₂]⁺ + e⁻ → Ag + 2NH₃
What is Fehling’s solution?
Blue solution of a complexed copper (II) ions dissolved in sodium hydroxide
What are the results when a ketone and aldehyde is mixed with Fehling’s solution?
Ketone - no visible change Aldehyde - brick red precipitate
What is the equation for when copper(II) ions are reduced, when used as Fehling’s solution?
Cu²⁺ + e⁻ → Cu⁺
What is Fehling’s solution similar too?
Benedict’s solution
What are the results when a ketone and aldehyde is mixed with Benedict’s solution?
Ketone - no visible change Aldehyde - brick red precipitate
What can you reduce an aldehyde too?
Primary alcohol
What can you reduce a ketone too?
Secondary alcohol
Give an example of a reducing agent used to reduce a aldehyde to a primary alcohol.
Sodium borohydride - NaBH₄
What is usually used to represent a reducing agent?
[H]
What is the mechanism called for when an aldehyde is reduced to a primary alcohol?
Nucleophilic addition
What from the reducing agent acts as a nucleophile for the mechanisms of an aldehyde being reduced to a primary alcohol
H⁻
What are the five steps in the mechanism for the reaction between an aldehyde and H⁻?
1.) The C=O bond is polar so the carbon is slightly positive and attracts the negative lone pair of electrons on the H⁻ ion 2.) The H⁻ ion attacks the slightly positive carbon and donates its pair of electrons forming a bond with the carbon 3.) As the carbon can only have four bonds this causes one of the carbon-oxygen bonds to break, forcing a lone pair of electrons from the C=O double bond onto the oxygen 4.) The oxygen then donates its lone pair of electrons to a H⁺ ion (which has come from from or a weak acid) 5.) And so a primary alcohol is produced
How can you produce hydroxynitriles?
By reacting aldehyde or ketones with hydrogen cyanide
What is produced when you react aldehydes or ketones with hydrogen cyanide?
Hydroxynitriles
What are hydroxynitriles?
Molecules which contain a hydroxyl group (OH) and a nitrile group (CN)
How do you name hydroxynitriles?
The nitrile group takes priority and so you name that with the suffix -nitrile, the carbon in the nitrile group is then carbon-1, you then name the hydroxyl group with the prefix hydroxyl- along with the number of the carbon atom it comes off
What is the mechanism called for when an aldehyde or ketone reacts with hydrogen cyanide to produce a hydroxylnitrile?
Nucleophilic addition
What are the six steps in the mechanism for when hydrogen cyanide reacts with an aldehyde or ketone?
1.) HCN is a weak acid so partially dissociates in water to form H⁺ ions and CN⁻ ions 2.) The C=O bond is polar so the carbon is slightly positive and attracts the negative lone pair of electrons on the CN⁻ ion 3.) The CN⁻ ion attacks the slightly positive carbon and donates its pair of electrons forming a bond with the carbon 4.) As the carbon can only have four bonds this causes one of the carbon-oxygen bonds to break, forcing a lone pair of electrons from the C=O double bond onto the oxygen 5.) The oxygen then donates its lone pair of electrons to a H⁺ ion 6.) A hydroxylnitrile is produced
What is often used instead of HCN? and why?
Acidified KCN HCN is extremely toxic and so KCN is used to reduce the risk and it is also easier to store Acidified to provide the H⁺ ions for the reaction
How should you heat aldehydes and ketones and why?
In a water both because they are very flammable
What functional group do carboxylic acids contain
-COOH
What suffix is used to name carboxylic acids?
-oic acid
What type of acids are carboxylic acids?
Weak
Why are carboxylic acids only weak acids?
They only partially dissociate into carboxylate ions and H⁺ ions
What do carboxylic acids react with carbonates or hydrogen carbonates to form?
A salt, carbon dioxide and water
What is the symbol for a carbonate ion?
CO₃²⁻
What is the symbol for a hydrogen carbonate ions?
HCO₃⁻
What can you react with a carboxylic acid to form a salt, carbon dioxide and water?
Carbonates or hydrogen carbonates
What is the equation for ethanoic acid reacting with sodium carbonate?
2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂
What is the equation for ethnic acid reacting with sodium hydrogen carbonate?
CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂
What is CH₃COONa?
Sodium ethanoate
How can you produce an ester from a carboxylic acid?
Heat in with an alcohol with a concentrated acid catalyst
What is produced when you heat a carboxylic acid with an alcohol and a concentrated acid catalyst?
Ester
How are esters named?
You name the first part with the alkyl group that came from the alcohol and then add the name of the carboxylic acid swapping the -oic acid for -oate
How do you name other functional group on esters?
Away from the C-O-C bond with both of these carbons being carbon-1
Name four uses of esters.
Perfumes, flavourings, solvents, plasticisers
Why are esters used in perfumes and as flavourings?
They can have a pleasant sweet smell
Why are esters used as solvents?
They are polar liquids so lots of polar organic compounds with dissolve in them, they also have a low boiling point so they an evaporate easily from the mixture
How are esters used as plasticisers?
They are added to plastics during polymerisation to make the plastics more flexible
What is hydrolysis?
When a substance is split up using water
What is the name for the reaction between an alcohol and carboxylic acid?
Esterification
As hydrolysis of an ester is often slow what is added to speed up the reaction?
An acid or alkali
What are the two types of hydrolysis called?
Acid hydrolysis and base hydrolysis