Organic Chemkstry II - Topic 17 Flashcards
Suffix of aldehydes
al
Suffix of ketones
One
Suffix and prefix of nitriles
Suffix - nitrile
Prefix - cyano
Suffix of esters
- yl - oats
Suffix for Acyl chloride
- oyl - chloride
Suffix for amide
Amide
Functional group of aldehyde
H - C = O
Functional group of ketone
C = O
Functional group of amines
C - NH2
Functional group of esters
O = C - O
Functional group of nitrile
C triple bond N
When do we use the prefix oxo to describe an aldehyde
The prefix oxo- should be used for compounds that contain a ketone group in addition to a carboxylic acid or aldehyde
When do we use the prefix hydroxy to describe an alcohol (or acid)
When there is an OH functional group and an additional functional group
What carbon atom is an aldehyde always on
One (hence why they always end in al and no number are used to describe the aldehyde)
When do you label the position of ketones in a compound
When there is 5 or more carbons in the carbon chain
What carbon does the C in the nitrile group count as
1 (so nitrile groups are never number)
How do you name esters
1) the chain after the single bonded oxygen is the alcohol formed so ends in yl and is at the beginning of the word
2) the chain after the double bonded oxygen is the carboxylic acid that is formed and ends in anoate and us at the end of the word
Chain isomers
Compounds with the same molecular formula but different structures of the carbon skeleton
position isomers
Compounds with the same molecular formula but different structures due to different positions of the same functional group on the same carbon skeleton
Functional group isomers
Compounds with the same molecular formula but with atoms arranges to give different
functional groups
Stereoisomers
same structural formulae but have a different spatial arrangement of atoms
Two types of stereoisomerism
- E-Z isomerism
- optical isomerism
Conditions for EZ isomerism
1) There is restricted rotation around the C=C double bond.
2) There are two different groups/atoms attached both ends of
the restricted double bond
Which atom is classed as higher priority in EZ isomerism
The atom with the higher relative atomic mass
What is the condition for optical isomerism to occur
- it has to contain a carbon compound with 4 different groups of atoms attached to a carbon (called a chiral carbon atom)
Enantiomers
Two compounds that are optical isomers of
each other
What are optical isomers
Isomers with similar physical and chemical properties, but they rotate plane polarised light in different directions
What is a racemate/racemic mixture
A mixture containing a 50/50 mixture of the
two isomers (enantiomers)
Will racemic mixture rotate in light
racemic mixture will not rotate plane-polarised light.
How do optical isomers rotate in plane polarised light
One optical isomer will rotate light clockwise. The other will rotate it anticlockwise(
How is a racemate formed
1) Nucleophilic addition of HCN to aldehydes and ketones when the trigonal planar carbonyl is approached from both sides by the HCN attacking species
2) When any attacking species approaches both sides for a trigonal planar reactant or intermediate
3) electrophilic addition of HBr to an unsymmetrical alkene
Why is racemate formed when attacking species approach both sides of the reactant or intermediate
As there is an equal chance of either enantiomer forming so a racemate forms
Draw and explain the SN1 mechanism of the formation of a racemate with 2-bromobutane and an OH ion
Pg 8 in chemrevise
Draw and explain the SN2 mechanism of the formation of a racemate with 2-bromobutane and an OH ion
Page 8 of chemrevise
Difference between SN1 and SN2 mechanism, for formation of racemate
- In SN2 no intermediates are formed instead the reaction occurs via a transition state (meaning that the molecule flips/turns to one side, which is the side the arrow on the Br is facing) whilst in SN1 intermediates are formed
- In SN2 If the reactant was chiral then during the reaction the opposite enantiomer would form. The product will rotate light in the opposite direction to the reactant
Draw and explain the electrophilllic addition of HBr to but-1-ene
Pg 8 of chemrevise
What are carbonyls
compounds with a C=O bond, they can be either aldehydes or ketones
What is the oxidizing agent that causes alcohols and aldehydes to oxidize
Acidified Potassium dichromate K2Cr2O7
What is primary alcohols oxidised into
Aldehydes
What is aldehydes oxidised into
Carboxylic acid
What is secondary alcohol oxidised into
Ketones
Test for aldehydes: oxidation using potassium dichromate
1) Reaction
2) Reagent
3) Conditions
4) Observation
1) aldehyde —> carboxylic acid
2) potassium dichromate (VI) solution and
dilute sulfuric acid
3) heat under reflux
4) Orange dichromate ion (Cr2O7 2-) reduces to green Cr 3+ ion
Test for aldehydes
- Tollens reagent
- Fehling solution
- potassium dichromate
Test for aldehydes: Tollens reagent
1) Reagent
2) Conditions
3) what happens to the aldehydes
4) observation
1) Tollen’s Reagent formed by mixing aqueous ammonia and silver nitrate ( [Ag(NH3)2]+ )
2) heat gently
3) aldehydes are oxidised by Tollen’s reagent into carboxylic acid and silver(I) ions are reduced to silver atom
4) a silver mirror forms coating the inside of the test tube, and there is no change to ketones
Test for aldehydes: Fehlings solution
1) Reagent
2) Conditions
3) what happens to the aldehydes
4) observation
1) Fehling’s solution containing blue Cu 2+ ions
2) heat gently
3) aldehydes are oxidised by Fehlings solution into a carboxylic acid and the copper ions are reduced to copper(I) oxide
4) aldehydes produce a blue Cu 2+ solution change to a red precipitate of Cu2O and Ketones do not react
Equation for the oxidation of aldehydes using Tollen’s reagent using ethanal
CH3CHO + 2Ag+ + H2O —-> CH3COOH + 2Ag + 2H+
Equation for the oxidation of aldehydes using Fehlings solution using ethanal
CH3CHO + 2Cu2+ + 2H2O —-> CH3COOH + Cu2O + 4H+
Full equation for oxidation of aldehydes using potassium dichromate with ethanal
3CH3CHO + Cr2O72- + 8H+ —-> 3CH3COOH + 4H2O + 2Cr
Reducing agents that will reduce carbonyls to alcohols
- NaBH4
- LiAlH4
Reduction of carbonyls/ carboxylic acids to primary alcohols
1) Reagent
2) Conditions
1) LiAlH4 in dry ether (or NaBH4)
2) Room temperature and pressure
Addition of hydrogen cyanide to carbonyls to form hydroxynitriles
1) Reaction
2) Reagent
3) Conditions
4) Mechanism
1) carbonyl —> hydroxynitrile
2) HCN in presence of KCN
3) Room temp and pressure
4) nucleophilic addition
What does the KCN do in the Addition of hydrogen cyanide to carbonyls to form hydroxynitriles
The extra KCN increases the concentration of the CN ion nucleophile needed for the
first step of the mechanis
Draw the nucleophilic addition of propanone to hydrogen cyanide
How do we form hydroxynitriles from carbonyls
Throughtnthe addition if hydrogen cyanide
What does the Iodoform test test for
Carbonyls with a methyl group next to the C=O
Iodoform test
1) Reagents
2) conditions
3) observations
1) Iodine and sodium hydroxide
2) warm very gently
3) The product CHI3 is a yellow crystalline
precipitate with an antiseptic smell
Iodoform equation for propanone
CH3COCH3 + 3I2 + 4NaOH → CHI3 + CH3COONa + 3NaI +3H2O
(The 3I2 + 4NaOH —> 3NaI + 3H2O stays the same in all Iodoform equations)
Iodoform equation with butan-2-one
CH3COCH2CH3+ 3I2 + 4NaOH → CHI3 + CH3CH2COONa + 3NaI +3H2O
Reaction to test whether a carbonyl is in an compound (test for both aldehydes and ketones)
Reaction with 2, 4-DNP
Observation with Reaction with 2,4-dinitro phenylhydrazine
An orange precipitate is formed in presence of aldehydes and ketones
How to identify what the carbonyl is after using 2, 4 DNP
1) differentiate an aldehyde from a ketone by using Tollen’s reagent or Fehlings
2) take the melting point of orange crystals product from 2,4-DNP. Compare melting point with known values in database
What happens the the solubility of carboxylic acids as the increase in size
Solubility decreases
Why do carboxylic acids dissolve in water
Due to the hydrogen bonding between the OH and C=O group
How do carboxylic acids remain stable (after dissolving in water)
When a carboxylic acid is dissolved in water it splits up into a carboxylic ion and a hydrogen ion. The lone pair of electrons from the O- ion and the electrons from the pi bond of the C=O become delocalised across the O=C-O bond and the charge is spread out this makes the ion more stable and makes dissociation more likely to occur
Explain the relationship with chain length and strength/ stability of carboxylic acids
Increasing chain length pushes electron density on to the COO- ion (as the oxygen are more electronegative) , making it more negative and less stable. This makes the acid less strong since there will be a greater attraction to protons (H+) so less dissociation.
Explain the affect of chlorine ions on the strength of carboxylic acids
Electronegative chlorine atoms withdraw electron density from the COO- ion, making it less negative and more stable. This make the acid more strong as there will be less attractions to the protons so it can dissociate more protons into the solution
Methods of preparing carboxylic acids
1) Full oxidation of Primary alcohols
2) oxidation of aldehydes
3) hydrolysis of nitriles
Full oxidation of primary alcohols
1) reaction
2) reagent
3) conditions
4) observations
1) primary alcohol —-> carboxylic acid
2) potassium dichromate(VI) solution and dilute sulfuric
3) an excess of dichromate, and heat under reflux: (distil off product after the reaction has finished)
4) orange dichromate ion (Cr2O7 2-) reduces to the green Cr 3+ ion
Hydrolysis of nitriles
1) Reaction
2) Reagent
3) Conditions
4) Equation with propanenitrile
1) Nitrile —> carboxylic acid
2) dilute hydrochloric/ sulfuric acid
3) heat under reflux
4) CH3CH2CN + H+ + 2H2O —-> CH3CH2COOH + NH4+
All example of salt formation with (carboxylic) acids
Acid + metal —> salt + hydrogen
Acid + alkali —> salt + water
Acid + carbonate —> salt + water + carbon dioxide
What is the only oxidizing agent that can oxidise carboxylic acid and why
- Methanoic acid
- as its structure contains and aldehyde group
What does carboxylic acids form when oxidized by methanoic acid
Carbonic acid
Reaction of carboxylic acid with phosphorus (v) chloride
1) reaction
2) reagent
3) conditions
4) equation with ethanoic acid
1) carboxylic acid —> acyl chloride
2) PCl5 (phosphorus (V) chloride)
3) room temp
4) CH3COOH + PCl5 —> CH3COCl + POCl3
Test for carboxylic acid
Reaction of carboxylic acid with phosphorous (V) chloride - it would produce misty fumes of HCl is carboxylic acids are present
How are esters formed
When Carboxylic acids react with alcohols, in the presence of a strong acid catalyst, to form
esters and water.
Use of esters
- perfume
- solvents
- flavouring
Reagents and conditions used for hydrolysis of esters
Reagents: dilute acid or dilute sodium hydroxide
Conditions: heat under reflux
Difference in the hydrolysis of esters with an dilute acid and sodium hydroxide
With acid - reaction is reversible and does not give a good yield of products (carboxylic acid and alcohol)
With sodium hydroxide - reaction goes to completion and it produces a carboxylic salt product, which is the anion of carboxylic acid, which is resistant to weak nucleophiles (e.g alcohols) so reaction is not reversible
Why are acyl chlorides more reactive than carboxylic acids
As the Cl group is a good leaving group
Reaction of acyl chlorides with water
1) reaction
2) reagent
3) conditions
1) acyl chloride —> carboxylic acid
2) water
3) room temp
Reaction of acyl chlorides with alcohol
1) Reaction
2) Reagent
3) Conditions
1) acyl —> ester
2) alcohol
3) room temp
Reaction of acyl chlorides with ammonia
1) reaction
2) reagent
3) conditions
1) acyl —-> primary amide
2) ammonia
3) room temp
Reaction of acyl chlorides with primary amines
1) reaction
2) reagent
3) conditions
1) acyl —> secondary amide
2) primary amine
3) room temp
Two types of condensation polymers
1) polyesters
2) polyamides
How do we form polymers
By reacting compounds with the same functional group on each end of the molecule
dicarboxylic acid + diol —-> poly(ester) + water
diacyl dichloride + diol —-> poly(ester) + HCl
How are polyesters hydrolysed
By using an acid or alkali
- with HCl a polyester will be hydrolysed and split up in to the original dicarboxylic acid and diol
- With NaOH an polyester will be hydrolysed and split up into the diol and dicarboxylic acid salt.
What is meant by a chiral molecules
A non superimposable molecule on its mirror image with no plane of symmetry
