Chem 4:5 - Compounds Containing the Carbonyl Group Flashcards
Carbonyl Group Formula
> C=O
What are carbonyl groups present in ?
Aldehydes and Ketones
Aldehydes Formula
H
> C = O
R
Ketones Formula
R
> C = O
R
What can the R groups on the aldehydes and ketones be ?
Alkyl or Aryl
How do you name aldehydes?
1) Suffix = al
2) FG counted as par of the C chain.
3) No numbers needed because the ald group is always at the end.
4) CH2O = methanal
How do you name ketones?
1) suffix = one
2) C atom of FG part of the C chain.
3) C3H6O = propanone
4) No ketone with less than 3 C’s possible
5) no need to number C in prop or but because it can only be in one position.
What do you know about the reactivity of the carbonyl compounds?
- Delta positive C makes it easy for nucleophilic reagents to attack.
- Double bond means additions reactions possible due to the unsaturated carbonyl group.
- Most common reaction in carbonyl groups = NUCLEOPHILIC ADDITION.
What can you use as the nucleophile for these nucleophilic addition reactions?
HCN/NaCN/KCN
Describe the mechanism for nucleophilic addition in words.
1) Arrow from Nu to C and arrow from double bond to O
2) C is now attached to Nu and O:-
Also arrow going from O to H+
3) Product is RR’CNuOH
What are the products of these nucleophilic addition reactions called?
Hydroxynitriles
What can the reaction produce?
A racemic mixture
- forms an aldehyde and an unsymmetrical ketone
- Because the CN ion may attack from above or below the C=O group.
What do these reactions do in terms of C chain length?
Increase it
What can aldehydes be oxidised to ?
what denotes the oxidising agent?
and what would the oxidising agent be?
Carboxylic acids
[o]
Potassium Dichromate (K2Cr2O7/H+) with dilute sulphuric acid.
Can ketones be oxidised to carboxylic acids? and why?
No
Because unlike Ald, a C-C bod must be broken.
What CAN oxidise ketones?
A stronger [o] can break ketones down into CO2 and H2O
This shortens the C chain
What tests can you use to distinguish aldehydes and ketones?
1) Fehlings test
2) Silver mirror test
What is Fehlings test?
Made from:
Fehlings A - Cu2+ (blue)
Fehlings B - alkali and complexing agent.
What is the silver mirror test?
Tollens Reagent
- Complex of silver nitrate and ammonia
- (Ag[NH3]2)
What occurs when an aldehyde is warmed with fehlings solution?
Brick red precipitate formed
- of Cu(I) oxide
- because copper oxide oxidises the aldehyde to a carbox acid.
- Cu(II) reduced to Cu(I)
What happens when ketones are warmed with fehlings solution?
No reaction
What happens when an aldehyde is warmed with tollens reagent?
Metallic silver formed
- Ald oxidised by tollens reagent
- Ag+ reducd to metallic silver
- Silver mirror formed on outside of test tube (spotlessly clean)
What is the reaction for an aldehyde and tollens reagent?
RCHO + [o]»_space;> RCOOH
What happens when a ketone is warmed with tollens reagent?
No reaction
Many reducing agent can reduce Aldehydes and ketones to alcohols, what is an eg of a reducing agent and how does it work?
Sodium tetrahydridoborate (NaBH4)
- In aqueous solution : H- ion formed.
- This attacks the C=O (but not C=C because its repelled by e density)
Describe the mechanism of reducing an aldehyde and what is the only difference in reducing a ketone
1) Arrow from :H- to C and double bond to O
2) arrow from RHCHO:- to H+
3)RHCHOH molecule formed.
- PRIMARY ALC formed
In an ester - a secondary alcohol is formed.
Formula of a carboxylic acid
COOH/CO2H
What do you know about the FG’s and the properties of carboxylic acids
Has 2 FG’s - OH and C=O
This means they have different properties.
Eg the OH is more acidic in CA’s than alcohols.
Look at flashcard to see how to name CA
Properties of CA’s
- Form H-bonds with water
- Up to butanoic acid are completely soluble in water
- CA in solid state form H- bonds with eachother therefore MP is higher than alkanes of similar RM
Identify the smells of ethanoic and butanoic acid.
Ethanoic acid = VINEGAR
Butanoic acid = RANCID BUTTER
Formula Of esters
RCOOR’
Compare Esters to CA’s
Esters derived from CA’s
H in the alc group of CA’s replaced by a hydrocarbon group (alkyl or aryl) therefore OH replaced by OR
What are the properties of esters?
Volatile ad have pleasant smells
Look in txtbk for smells
look at flashcard for how to name esters
What 3 things do you know about the reactivity of carboxylic acids?
1) delta positive carbon can be attacked by a nucleophile
2) Delta negative O can be attacked by charge species eg H+
3) Can act as an acid and lose a proton
How are esters formed? and why is an equilibrium formed?
CA reacts with an alcohol
Sped up by strong acid catalyst.
Reversible reaction
The H from the OH group substituted for the hydrocarbon grp on the alcohol
read flashcard about hydrolysis of esters NOW
Hydrolysis of esters
Delta positive carbon gets attacked by water acting as a weak nucleophile.
RCOOR’ +H2O»_space;» RCOOH +R’OH
An equilibrium is produced because the reaction doesn’t go to completion.
An acid catalyst is used - speeds up rate at which eq reached but doesn’t change composition of elements
How do you name carboxylic acids?
1) CA group counted as part of the carbon chain
2) CA Carbon is counted as the 1st C if it has any side chains
Eg. HCOOH - Methanoic acid
How do you name esters?
1) Based on the parent acid therefore the name always begins with the alkyl/aryl group that has replaced the hydrogen from the carboxylic acid
2) Eg CH3COOCH3 =Methyl (from he alkyl/aryl group) Ethanoate because theres 2 carbons attatched to the CH3.
How does a carboxylic acid act as a proton? And what do you know about the resulting ion?
- H from OH group is lost to form a Carboxylate ion : RCOO-
- Therefore now the negative charge is shared over the whole molecule
- The delocalisation makes the ion very stable.
Carboxylic acids are weak acids, therefore the equilibrium lies well to the left. But what are they still able to do ?
React with sodium hydrogen carbonate and release CO2. This distinguishes them from other organic groups that contain OH (eg Alcohols)
What is the equation when ethanoic acid (carboxylic acid) reacts with sodium hydrogen carbonate?
CH3COOH + NaHCO3»_space;»> CH3COONa + H2O + CO2
Carboxylic acids are proton donors therefore they act as acids, how does this work?
-They form ionic salts with reactive metals/alkalis/metal oxides/metal carbonates
-Salts formed have the general name CARBOXYLATES.
Eg methanoic acid = methanoates
ethanoic acid = ethanoates etc
What would the equation be between ethanoic acid and sodium hydroxide?
CH3COOH + NaOH»_space;»» CH3COONa + H2O
Hydrolysis of esters part 2
- Esters can be hydrolysed at room temperature using strong acid catalyst.
- Base can also be used as catalyst but produces the salt of the acid instead of the acid therefore the reaction goes to completion.
2 equations showing hydrolysis of esters using strong acid catalyst and base
1) CH3COOCH3 + H2O»_space;(reversible reaction)»(base catalyst - NaOH)»> CH3COONA + H2O
Uses of esters
- Animal and veg oils = Esters of propan 1,2,3 - triol (glycerol)
What are the difference between fats and oils
?
Fats are solid at RT
Oils are liquid at RT
What do fats and oils contain?
3 molecules of long chain CA’s - FATTY ACIDS
What are oils and fats called?
Triglycerides
Can fats and oils be hydrolysed in acid conditions? and if so, what are the products
yes, Fatty acids and glycerol
Can fats and oils be hydrolysed with boiling with NaOH? if so, what are the products?
yes, Glycerol and a mixture of the salts that made up the esters
What are the salts? And what makes the salt the type it is
soaps
the amount of fatty acid originally in the ester
Properties of glycerol
3 O-H bonds therefore readily forms Hydrogen bonds
V soluble in water
Uses of glycerol
Pharmecutical products (attracts waters therefore stops creams from drying)
Solvent in medicines and present in toothpaste
Solvent in food industry - food colouring
Plasticies
Acyl Group?
RC(x2bondO) and something else
What is acylation?
where an acyl group is introduced to another molecule
all acid derivatives have an acyl group, what are 2 other acid derivatives?
Acid chlorides
acid anhydrides
What are acid derivatives?
Derived from carboxylic acids
Formula RCOZ (Z can be a variety of groups)
if Z was CH3 then molec called - ETHANOYL
Why is an acid derivative susceptible to nucleophilic attack?
Because it is polarised (delta C positive and negative delta O)
The Z is replaced by the nucleophile
How readily this acid derivative nucleophilic substitution reaction is dependant on 3 factors, what are they??
1) magnitude of Delta positive carbon
2) how easily Z is lost
3) Hoe good the nucleophile is
What 2 things make a good nucleophile
1) Lone pair to attack e- deficient carbon
2) Good at donating its lone pair
What 4 molecules do acid cl and acid anhydrides react with ?
NH3 - ammonia
NH2R - Primary amine
H2O - Water
HOR- Alcohol
What are the reactions of nucleophiles and acid anh/cl called?
Addition elimination reactions
NOW READ FLASHCARDS FOR MECHANISMS
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