Chemistry- Alcohols, Aldehydes, Ketones and carboxylic acids Flashcards
What is the primary, secondary and tertiary structure of an alcohol?
Primary: R-OH
Secondary: RCH(OH)R’
Tertiary: RC(OH)R’R”
What are the alcohols (primary, secondary and tertiary) oxidised to?
Primary —[O]—>Aldehyde—[O]—> Carboxylic acid
Secondary —[O]—> Ketone
Tertiary (cannot be oxidised)
Oxidation reagents:
Acidified Potassium Dichromate
What is the test for an oxidation reaction of an alcohol & determining what alcohol structure there is?
Tollens- (silver Nitrate / NH3) = silver mirror or black precipitate
Benedicts/Fehlings = Brick Red precipitate
What are the tests for an Aldehyde?
Fehlings / Benedicts reagent
- Brick red / orange precipitate
Tollens reagent
- Forms a mirror (for positive result)
What is the test for tertiary alcohols?
Reaction with sodium carbonate solution.
Tertiary alcohols effervesce
What happens during oxidation of a primary alcohol?
Primary alcohol —[O]—> Aldehyde
Aldehydes can be distilled off after reflux reaction of a primary alcohol.
Aldehyde —[O]—> Carboxylic Acid,
If not distilled and alcohol is oxidised to completion then a carboxylic acid forms.
What is the functional group for an Aldehyde?
RCHO
What happens during the oxidation of a secondary alcohol?
Alcohol —[O]—> Ketone
Formed when secondary alcohols are heated under reflux.
What is the Functional group for a ketone?
R-C(-R)=O
What happens during the oxidation of a tertiary alcohol?
Tertiary alcohols do not oxidise (no change)
How can you test for a primary, secondary or tertiary alcohol or aldehydes and ketones?
1) Heat with H2SO4/ K2Cr2O7 No colour change = 3' alcohol. 2) Green solution 2' or 1' alcohol 3) distil and test with tollens or Fehlings No colour change = 2' Alcohol Colour change = 1' Alcohol.
Why are only small ketones and aldehydes soluble in water?
The smaller ketones and aldehydes can form hydrogen bonds in water due to electronegative oxygen atoms in their structure bonding to water molecules.
Larger aldehydes and ketones with large R-groups (hydrocarbon chain) are less soluble as the longer chain is non-polar and cause solubility to decrease.
What intermolecular forces are present in an alkane, ketone and alcohol and their effect on their boiling points
Butane - Only van der waals forces so have a low boiling point
Ketone - Dipole dipole forces and van der waals so middle boiling point
Alcohol - Hydrogen bonds and van der waals so high boiling point.
Why are ketones and aldehydes susceptible to attack from nucleophiles?
C=O is a polar bond due to electronegativity between carbon and oxygen.
Nucleophiles attack the slightly positive carbon and the double bond means that an addition reaction is possible.
Why is the nucleophilic addition of cyanide useful?
Very useful due to the number increase in carbon number within the molecule.
Nitrile and hydroxy can react at a later date.
What isomers are produced from nucleophilic addition with cyanide?
Nucleophilic addition with cyanide to an aldehyde or asymetric ketone produces optical isomers.
Nucleophilic addition to a symetrical ketone does not produce an optical isomer.
What kind of mixture is produced when a nucleophile reacts with an asymetric isomer.
50% : 50%
Racemic mixture
What is the carbon with 4 different groups off it called?
Chiral carbon (chiral centre)
Why is HCN gas not used practically or in a lab?
Toxic gas and hard to prevent escaping into the laboratory.
What substances are used to introduce cyanide into a molecule.
Use NaCN or KCN followed by dilute HCl.
Na/KCN —> Source of CN ions
Dilute HCl —> Source of H+ ions
What is the reverse reaction to oxidation and what is the reducing agent?
Reduction reaction
Hydride ion H-
What source of Hydride ions is used in reduction of carbonyl gorups? (C=O)
NaBH4
Sodium Tetrahydrioborate III
Why would NaBH4 not reduce Alkenes (C=C) bonds?
Hydride ion (H-) is negative and therefore will not react/attack electron dense area on the pi bond of C=C.
Define a chiral molecule
A molecule where a carbon has 4 different groups attached called a chiral centre or Asymetric carbon
Define a Racemic mixture
Where a 50:50 mixture of two (optical isomers) is produced. A mixture of 50:50 enantiomes.
Optical Isomers often produced from nucleophilic addition.
Explain why carboxylic acids are soluble in water
Due to the carboxyl group RCOOH being able to form hydrogen bonds with water molecules.
Carboxylic acids with < 4 carbon atoms are completely soluble in water. >4 carbon atoms cause the molecule to become less and less polar and therefore lose solubility.
What is special about Carboxylic acids boiling points compared to Alkanes of a similar Mr?
Carboxylic acid boiling points are much higher than alkanes of a similar Mr.
Since carboxylic acids can form hydrogen bonds therefore increase their boiling point compared to easily overcome van der waals forces of attraction.
What can be formed form carboxylic acid molecules in a pure carboxylic acid?
May form Dimers (2 monomers joined together by a hydrogen bond)
What is the test for a Carboxylic acid?
Add sodium carbonate solution.
The carboxylic acid is present if effervescence occurs with sodium carbonate.
Describe the reaction equation between magnesium and ethanoic acid.
Mg + 2CH3COOH —(H2O)—> (CH3COO-)Mg^2+ + H2
Until water is added, ethanoic acid is not dissociating easily. Adding H2O causes an equilibrium shift to the right and more product (magnesium ethanoate) is produced.
How is an ester formed?
Alcohol + Carboxylic Acid Ester + Water
An acid catalyst is used in formation.
Why is a base hydrolysis of an ester better than a metal and a carboxylic acid?
Base hydrolysises of esters are better as this will go further to completion since no equilibrium forms
What is the structure of soap?
Sodium/Potassium salt of a fatty acid.
(Na+O-)-C(-R)=O
Hydrophilic ionic end (polar) and hydrophobic hydrocarbon end (non-polar)
What is formed from the base hydrolysis of a triglyceride?
Heating with Sodium Hydroxide = A Hard Soap
Heating with Potassium Hydroxide = A soft soap
What are the products of a base hydrolysis of triglyceride?
Soap
Glycerol (Propan-1,2,3-triol)
What are the uses of Propan-1,2,3-triol?
Solvent in food Pharmaceutical applications Attracts water Prevents foods from drying out Plasticiser in PVC and other plastics.
How does Soap Work?
- Soap interacts when in between oil and water.
- Carboxylate ion end dissolves in water and hydrocarbon end dissolves in oil.
- This stabilises the oil droplets as soap ions arrange themselves around each droplet of oil.
- Each droplet is surrounded by a negative charge so droplets repel each other.
- Hydrogen bonds form with water molecules so the oil droplets can be removed.
How do you make biodiesel?
Methano l + vegetable oil —> Methyl Ester + Glycerol
Animal Fats (Biodiesel)
Waste oil
Similar to making soap -> makes methyl esters and not sodium salts.
How does biodiesel form?
After the reaction between the triester/trigylceride
- 2 layers form.
Glycerol is denser than the methyl ester and therefore biodiesel forms a layer ontop of glycerol (propan-1,2,3-triol.
Why do Methyl Esters not dissolve in gylcerol?
Methyl Esters could form hydrogen bonds with glycerol however the length of the R-gorups are too long (non-polar sections) so solubility is prevented.
Define a nucleophile.
A species which is an electron pair donor (usually a negative ion and/or has a lone pair)
Define an Electrophile
A species which is an electron pair acceptor (usually an electron deficient ion/molecule)
They attack areas of high electron density.
What is an addition reaction?
Where you could chemically add one molecule into another molecule.
(1 molecule formed as a product of 2 molecule)
What is an elimination Reaction?
Remove a molecule from another molecule to form 2 separate molecules.
What is a substitution reaction?
Where one molecule is swapped/substituted for another molecule.
What is an Acyl group?
R-C=0(-Z) where z can be anything.
Give some examples of Acyl molecules.
Ester: RCOOR Ethyl Ethanoate
Acyl Chloride: RCOCl Ethanoyl Chloride
Acid Anhydride RCOOCOR Ethanoic Anhydride
They are all acid derivatives made from carboxylic acids.
What is Acylation?
The process by which an acyl group is introduced into another molecule.
What are the possible nucleophiles for an acylation reaction?
Water - Produce carboxylic acids
Alcohol - Produce esters
Ammonia - Produce amides
Amines - Produce N-substituted amides.
What is the functional group of an Amide?
O=C-N-H
