11 Aldehydes and Ketones Flashcards
What do carbonyl compounds contain?
a carbonyl group (C=O)
Give two compounds containing a carbonyl group (C=O).
aldehydes
ketones
Compare aldehydes and ketones by:
a) polar carbonyl group
b) how it reacts
c) whether it can be further oxidised
aldehydes: a) polar carbonyl group RCHO b) nucleophilic addition c) can be further oxidised ketones: a) polar carbonyl group RCOR' b) nucleophilic addition c) cannot be further oxidised
Where is the carbonyl group located in aldehydes as a pose to ketones?
in an aldehyde, it is at the end of the carbon chain
in an ketone it is within the carbon chain
State what each of the following represents:
a) C=O
b) CHO
c) R
d) R’
a) C=O: carbonyl f.group
b) CHO: aldehyde f.group
c) R = H, alkyl, aryl
d) R’ = alkyl or aryl (can’t be hydrogen)
What is common carbonyl compound formaldehyde manufactured from and used as? State the structure.
(Hint: Meth lab and cadavers)
manufactured from methanol
used in many polymers, disinfectant and tissue fixation
(see doc for structure)
What is common carbonyl compound acetaldehyde prepared from and formed in? State the structure.
(Hint: in the body)
prepared from ethyl alcohol
formed in the detoxification of alcohol in the liver (=hangover)
(see doc for structure)
What common carbonyl compound forms acetone, where is it excreted and what is it used in? State the structure.
(Hint: makes you smell of pear drops)
formed in the human body as a by-product of lipid metabolism
excreted in the urine and breath
laboratory use
(see doc for structure)
Which common carbonyl compound hormones are used? give examples for each. Draw out the structures too.
(Hint: ketone = end in -erone)
(Hint: men are simple/ women more complex and stress hormone is stressful to memorise)
(Hint: makes you smell of pear drops; a popular diet atm)
steroid hormones e.g. progesterone, testosterone, cortisone
metabolites e.g. pyruvate, α-ketoglutarate
(see doc for structures)
Which common carbonyl compound are carbohydrates and what are they composed of? Give examples for each. State the structure.
(Hint: each must have 6 C atoms)
carbohydrates are composed of polyhydroxy aldehydes or ketones
e.g. glucose and fructose
(see doc for structures)
Describe the bonding in the carbonyl (C=O) bond.
Hint: 1 pi-bond has 2 balloons and unhybridsed bonds are free bonds
carbon and oxygen are sp2 hybridised
C=O bond comprises a σ-bond and a π-bond
σ-bond is formed by the overlap of sp2 orbitals of carbon and oxygen
π-bond is formed by the overlap of unhybridised p-orbitals
Describe the bond angle and how electrons are shared in carbonyl (C=O) compounds.
bond angles are carbon 120°
electrons in C=O are not shared equally
Describe the electronegativity of the carbonyl (C=O) bond.
electronegative oxygen results in polar bond
How would you give an IUPAC name to an aldehyde.
IUPAC: the -e in the corresponding alkane is replaced by -al.
How would you give a common name to an aldehyde.
derived from the names of corresponding carboxylic acids by replacing -ic acid by -aldehyde.
For each of the following aldehydes state the IUPAC and common names:
a) HCHO
b) CH₃CHO
c) CH₃(CH₂)₂CHO
a) IUPAC: methanal Common: formaldehyde b) IUPAC: ethanal Common: acetaldehyde c) IUPAC: butanal Common: butyraldehyde
How would you give an IUPAC name to a ketone?
the -e in the alkane name is replaced with –one.
The location of the group in the chain is indicated by the number before the -one
How would you give a common name to an ketone?.
the word ketone is added after naming the alkyl groups attached to the carbonyl group
(not necessarily listed in alphabetical order!)
For each of the following ketones (on the document) state the IUPAC and common names.
a) IUPAC: Butan-2-one Common: Methyl ethyl ketone (MEK) b) IUPAC: Propanone Common: Acetone (dimethyl ketone)
Draw out the general reaction for oxidation of a primary alcohol and state:
a) what is lost
b) the 2 possible chemical reagents
c) the 2 possible biological reagents
(see document for diagram)
a) a H atom
b) examples, K₂Cr₂O7 or pyridinium chlorochromate (PCC)
c) Alcohol dehydrogenase + NAD(P)+
Draw out the general reaction for oxidation of a methylaromatic and state the chemical reagent
(see document for diagram)
the chemical reagent is H⁺/Na₂Cr₂O7
Draw out the general reaction for the reduction of an acid chloride molecule and state:
a) the 2 possible chemical reagents
(Hint: Li and Al Have over the top Boos x3 OR How Pda is ad Sign Off x4)
(see document for diagram) a) the chemical reagents are: LiAlH(OtBu)₃ OR H₂, Pd-BaSO₄
Draw out the general reaction for oxidation of a secondary alcohol.
(see document for diagram)
Draw out the general Friedel-Crafts acylation (Aryl only) reaction.
(see document for diagram)
Draw out the general reaction for ketone synthesis by coupling of an organometallic (“R-”) with a carboxylic acid derivative and state:
a) the reagents
b) draw the general reaction equation
a) R’₂CuLi
b) see document
Where is the biological version of ketone synthesis by coupling of an organometallic (“R-”) with a carboxylic acid derivative used? Draw out the reaction example.
For polyketide and fatty acid biosynthesis
see document for the reaction example
State the physical properties of aldehydes/ketones in terms of boiling point.
boiling points are affected by the carbon-oxygen double bond is very polar
Higher than ethers (C-O bonds)
Lower than alcohols (hydrogen bonding)
State the physical properties of aldehydes/ketones in terms of odour and what is the application of this.
Strong and characteristic
Many aldehydes and ketones used as fragrances and flavourings
Give 3 examples of ketones/aldehydes used as fragrances and flavourings and draw out their structures.
nonanal - roses
vanillin
rasberry ketone
(see document for structures)
State and explain the physical properties of aldehydes/ketones in terms of solubility.
Similar to alcohols
As carbonyl oxygen forms H-bonds with water
State and explain the key concepts of the chemical properties of aldehydes/ketones in terms of their reactions.
Carbonyl compounds are unsaturated and polar
Undergo nucleophilic attack resulting in addition to the C=O double bond.
Draw the polar charges on the C=O bond.
see document
Compare for alkenes and carbonyl groups by stating their respective:
a) bond
b) polarity
c) attacked by
d) results
a) alkene = C=C carbonyl = C=O b) alkene = non-polar carbonyl = polar c) alkene = electrophiles carbonyl = nucleophiles d) alkene = addition carbonyl = addition
In which 2 ways can the carbonyl bond also undergo aside from nucleophilic addition?
α-substitution
condensation
Draw out and describe in 2 steps the mechanism of nucleophilic addition to carbonyl compounds and name the product.
Step 1: CN¯ acts as a nucleophile and attacks the slightly positive C. The C=O pi bond breaks; a pair of electrons goes onto the electronegative O.
Step 2: A pair of electrons from O is used to form a bond to H+. Overall, there has been addition of HCN across the double bond.
Product: cyanohydrin
(see document for mechanism)
Which compounds readily dissolve in water and do they form?
Formaldehyde dissolves readily in water
Acetaldehyde somewhat also
form hydrates
Draw out the general hydration reaction for formaldehyde and state:
a) the reagent
b) draw the general reaction equation
c) the type of reaction and what it forms
a) addition of water (H₂O)
b) see document
c) nucleophilic addition, forms hydrates
Fill in the following table with the products and intermediates and their names for the reactions between aldehydes/ketones and alcohols twice?
see document
Give 2 examples of mixed acetals are present in biological strcutures.
(Hint: ultrastrcuture of plants and animals)
DNA
Cellulose
What is the biological relevance of ketones/aldehydes?
sugars - i.e. glucose and fructose
State the 3 stages of oxidation of primary alcohols.
primary alcohol → aldehyde → carboxylic acid
State the 3 stages of oxidation of secondary alcohols.
secondary alcohol → ketone → no more oxidation
State the oxidising agents used for oxidising alcohols:
a) chemically
b) biologically
a) chromate or permanganate oxidising agent
b) Aldehyde dehydrogenase (ALDH) + NAD(P)+
What is the lab test for aldehydes?
chromate or permanganate oxidising agent changing from green to orange
What is the Tollen’s reagent test?
Aldehyde → Carboxylic acid
Silver mirror formed from a clear solution
Tollens reagent = silver nitrate (AgNO₃), aqueous ammonia (NH₃ (ag)), NaOH
Write out the (balanced) Tollen’s reagent test equation.
see document
What is Benedict’s reagent test for reducing sugars? (Hint = in alphabet B then C)
Benedict’s reagent = CuSO4 + alkaline citrate
Solution changes from blue to brick red
What is the Fehling’s reagent test for reducing sugars?
Fehling’s reagent = CuSO4 + alkaline tartrate
Solution changes from blue to brick red
How do you know if a sugar is a reducing sugar from its structure?
Has C=O bond in it
Write out the (balanced) Fehling’s/Benedict’s reagent test equation
see document
State how aldehyde and ketone reductions occur:
a) what is needed?
b) chemically (the different possible reagents)
c) biologically
a) Need Source of H₂ or H-/H+
b) NaBH4, LiAlH4, Diisobutylaluminium hydride (DIBAL); H2 and Pd/Pt/Ni
c) NAD(P)H
Draw out the mechanism for aldehyde/ketone reduction including curly arrows.
see document
What are the two types of α-substitutions that can occur?
Aldol addition + condensation
What do aldehydes/ketones undergo with themselves?
Undergo self-addition in the presence of an acid or base (or enzyme)
Draw out the 3-stage self-addition reaction equation for the self-addition of acetaldehyde.
see document
Draw out the mechanism of the self-addition of acetaldehyde and state the molecules involved.
see document
Mechanism involves enol or enolate
What is an enolate?
R=C(O-)H
Describe the electronic properties of an enolate molecule.
Electron density on O and C
Act as a carbon nucleophile
(see document for the diagram)
State and draw out the 2 examples of biological carbon-carbon bond formation.
(Hint: first stack together and then opposite splitting)
Carbohydrate metabolism - aldolases
see document for them
State a medical example for testing for ketones and how do they work?
Urinalysis sticks used by diabetics and dieters
Work by an enolate reaction
State the ketone reaction for urinalysis sticks to work and the enzymes.
see document
