Organic chemistry- Carbonyl and carboxylic acids Flashcards
what is the functional group of aldehydes?
carbon atom of carbonyl group is attached to a hydrogen atom
what is methanal used for?
used in solution to preserve biological specimens
what is the functional group for a ketone?
carbonyl functional group is joined to two carbon atoms
what is propanone used for?
it is acetone, which is used as a solvent and used in nail varnish removers
what is octantal used for?
colourless fragrant liquid, responsible for the smell of oranges. It naturally occurs in citrus oils and is used in perfumes and flavour production in food industry
Why do ketones not undergo oxidation reactions?
lack of reactivity
What is the difference between the C=C double bond in alkenes and the C=O in carbonyl compounds?
-C=C in alkenes is non-polar
-C=O in carbonyl compounds is polar
-oxygen is more electronegative than carbon, greater share of electrons causing separation of charge.
why do aldehydes and ketones react with some nucleophiles?
due to polarity of C=O double bond. The reaction is called nucleophilic addition
what reducing agent is used to reduce aldehydes and ketones into alcohols?
Aldehyde or ketone is warmed with NaBH4 (sodium tetrahydridobrorate III) in aqueous solution
Aldehydes reduce to?
primary alcohols
Ketones reduce to?
secondary alcohols
Describe hydrogen cyanide?
HCN, it is colourless and poisonous. It cannot be used in an open laboratory as it boils slightly above room temp. Sodium cyanide and sulfuric acid are used to provide hydrogen cyanide.
Why is the reaction between carbonyl compounds (aldehydes and ketones) and hydrogen cyanide useful?
Increases length of carbon chain. A nitrile group (CN) and hydroxyl group is formed. These compounds are classed as hydroxynitriles
What is a carbonyl compound?
compound with C=O
In the nucleophilic addition reaction with NaBH4, what acts as the nucleophile?
hydride ion, H-
Describe the mechanism for the reaction between NaBH4 and carbonyl groups?
-hydride ion is attracted and donated to positive carbon atom
-dative covalent bond is formed between hydride ion and carbon atom of C=O double bond
-the pi C=O bond breaks by heterolytic fission forming a negative intermediate
-the oxygen atom of the intermediate donates a lone pair of electrons to a hydrogen atom in a water molecule. The intermediate becomes protonated to form an alcohol and lone hydroxyl group.
Describe the mechanism for the reaction with NaCN/H+?
-the cyanide ion, CN- is attracted to the C=O and a dative covalent bond form
-the pi bond breaks through heterolytic fission forming a negatively charged oxygen
-the immediate (oxygen) is protonated by a lone pair of electrons from a hydrogen ion.
-a hydroxynitrile is formed
How do you detect carbonyl compounds?
use Brady’s reagent . Positive result of yellow or orange precipitate
Describe Brady’s reagent?
normally dissolved in methanol and sulphuric acid as a pale orange solution. Solid Brady’s reagent is very hazardous due to friction or sudden blow causing explosion
How does Brady’s reagent work?
in condensation reaction as water is formed in nucleophilic addition. The NH2 group in Brady’s reagent adds across the C=O
how do you detect and aldehyde?
using tollen’s reagent, a solution of silver nitrate in aqueous ammonia. Positive result of a silver mirror
What are the reactions when using tollens reagent?
Ag+ acts as oxidising agent in presence of ammonia. Silver ions are reduced to silver and aldehyde is oxidised to carboxylic acid
what are the chemical equations when using tollens reagent?
-Ag+(aq) + e- —> Ag(s) (silver mirror)
-aldehyde + [O] —-> carboxylic acid
what is the functional group for a carboxylic acid?
contain carbonyl group and hydroxyl group on the same carbon
carboxylic acids are used for?
medicines e.g painkiller (aspirin)
why are carboxylic acids soluble?
the C=O AND O-H bonds are polar, allowing hydrogen bonds to form with water molecules
why does solubility decrease as number of carbon atoms increases?
carboxylic acids with up to four carbon atoms are soluble in water. The non-polar carbon chain has a greater effect on the overall polarity
what kind of acid are carboxylic acids?
weak acids, they partially dissociate from H+ ions
carboxylic acids take place in redox reactions with…
metals. They form hydrogen gas and carboxylate salt.
carboxylic acids take place in neutralisation reactions with…
bases (alkalis, metal oxides, carbonates)
carboxylic acids form what kind of salt?
carboxylate salts
carboxylic acid + metal oxide forms?
carboxylate salt + water
carboxylic acid + alkali forms?
carboxylate salt + water
carboxylic acid + carbonate forms?
carboxylate salt + water +carbon dioxide
how do you test for a carboxyl group?
react with carbonate. Carboxylic acids are the only common organic compound sufficiently acidic to react with carbonates
what Is a devrivative of a carboxylic acid?
a compound that can be hydrolysed to form the parent carboxylic acid.
what is an acyl group?
common sequence of atoms in the structure
how do you name esters?
replace -ioc acid from -oate. The alkyl chain attached to the oxygen atom of the COO group is then added as the first word in the name
how do you name acyl chlorides?
replace -oic acid with -oyl chloride
how is an acid anhydride formed?
by removal of water from two carboxylic acid molecules
what is esterification?
reaction of alcohol and carboxylic acid where is is warmed to form an ester an water. Use small amount of concentrated sulphuric acid which acts as a catalyst.
what does esters smell like?
sweet smelling
how can you easily detect the smell of an ester when making it from a carboxylic acid and alcohol?
add aqueous sodium carbonate which is a weak base to neutralise acid. This removes the smell of the carboxylic acid that hasn’t reacted making it easier to smell the ester.
describe ethyl propanoate (common)?
colourless. Smells like pineapples. It is naturally produced in some fruits like kiwi and strawberries
esters can be hydrolysed by what?
aqueous acid or alkali
Explain the hydrolysis of ester using acid
ester is heated under reflux with dilute aqueous acid. The ester is broken down by water with acid acting as a catalyst.
what are the products of the acid hydrolysis?
carboxylic acid and alcohol
Explain the alkaline hydrolysis is also known as saponification
it is irreversible. The ester is heated under reflux with aqueous hydroxide ions.
what are the products formed when an ester is hydrolysed using an alkaline?
carboxylate ion and an alcohol
describe the oxidation of aldehydes?
can form carboxylic acids when refluxed with acidified dichromate ions usually potassium or sodium and dilute sulphuric acid.
do ketones undergo oxidation reactions?
no
what is the chemical test and observation of an alkene?
chemical test- bromine water
observation- colourless
what is the chemical test and observation of an aldehyde?
test- tollens reagent and warm
observation- silver mirror
what is the chemical test and observation of a carbonyl?
test- 2,4 DNP
observation- orange precipitate
what is the chemical test and observation for a primary and secondary alcohol and aldehyde?
test- acidified potassium dichromate and warm in water bath
observation- orange precipitate
what is the chemical test and observation from a carboxylic acid?
test- aqueous sodium carbonate
observation- effervescence
