Chapter 17 Flashcards
What is optical isomerism a type of?
Stereoisomerism
What is sterioisomerism?
Where isomers have the same structural formula, but the atoms are arranged differently in space
What is a chiral carbon atom also known as?
A chiral centre
What is a chiral centre?
A carbon atom that has 4 different groups attached to it
What are enantiomers also called?
Optical isomers
What are optical isomers?
Isomers which are mirror images of each other and come from chiral centres
What are the 2 steps you have to take when drawing optical isomers?
1-Locate chiral centres
2-Draw one enantiomer in a tetrehedral shape, then draw a mirror image of it
What is normal light made up of?
A range of different wavelengths and vibrates in all directions
What is monochromatic, plane-polarised light made up of?
Light of a single wavelength and only vibrates in one direction
As optical isomers are optically active, what do they do?
They rotate the plane of polarisation of plane-polarised monochromatic light
What do optical isomers do to plane-polarised monochromatic light?
One enantiomer rotates it clockwise whilst the other rotates it anticlockwise
What is a racemic mixture?
A mixture which contains equal quantities of each enantiomer of a chiral compound
Why don’t racemic mixtures rotate plane-polarised light?
The two enantiomers cancel out each others light-rotating effect
What do chemists often get when mixing 2 achiral things together?
A racemic mixture of a chiral product, as there is an equal chance of forming each of the enantiomers. For example, butane and chlorine form HCl + either enantiomer.
What happens in the Sn1 mechanism roughly?
You start with a single enantiomer and form a racemic mixture of 2 optical isomers of each other
What happens in step 1 of the Sn1 reaction?
A group breaks off, leaving a planar(flat ion). This group could be X-
What happens in step 2 of the Sn1 mechanism?
The planar ion can be attacked by a nucleophile from either side, resulting in 2 optical isomers
What happens in the Sn2 meachanims roughly?
A single enantiomer reactant produces a single enantiomer product
What happens in the only step of the Sn2 mechanism?
The nucleophile attacks the opposite side to the leaving group(X-), so only one product is produced. The product will rotate plane polarised light differently to the reactant
What do both aldehydes and ketones contain?
A carbonyl group
What is a carbonyl group?
A C=O bond
What is the difference between the structure of aldhydes and ketones?
Aldehydes have their carbonyl group at the end of the carbon chain, ketones have it in the middle of the carbon chain
What do aldehydes end in when naming>
-al
What do ketones end in when naming?
-one
Why can’t aldehydes or ketones form hydrogen bonds with other aldehyde or ketone molecules?
They don’t have a polar O-H bond
Why do solutions of aldehydes or ketones have lower boilng points than their equivalent alcohols?
The lack of hydrogen bonding
Which ways can ketone and aldehydes bond to other ketone and aldehyde molecules?
Through London forces and permanent dipole-permanent dipole bonds
What has a higher boiling temperature, propanone or propan-1-ol?
Propan-1-ol, as it contains hydrogen bonds
As aldehydes and ketones have a lone pair of electrons on the oxygen atom, what does this allow them to do?
Form hydrogen bonds with hydrogen atoms on water molecules
Why can some small aldehydes and ketones dissolve in water?
Their lone pair of electrons on the oxygen atom can form hydrogen bonds with the hydrogen atom in water
Why can’t larger aldehydes and ketones dissolve in water?
They have longer carbon chains which aren’t able to form hydrogen bonds with water. The carbon chains disrupt the hydrogen bonding between the water molecules, but aren’t able to form hydrogen bonds themself
Desribe why and aldehyde or ketone won’t dissolve in water:
If the aldehyde/ketone is large enough, the inntermolecular forces between the aldehyde/ketone molecules, and the hydrogen bonding between the water molecules will be stronger than the hydrogen bonds it could form with the aldehyde/ketone the compound won’t dissolve
What is the easiest thing to distinguish between an aldehyde and a ketone?
An aldehyde will easily be oxidies to a carboxylic acid, whilst a ketone won’t
What is Tollen’s reagent?
A colourless solution of silver nitrate dissolved in aqueous ammonia
If Tollen’s reagent is heated in a test tube with an aldehyde, what will happen?
A silver mirror forms after a few minutes
What is fehling’s solution?
A blue solution of complexed copper(II) ions dissolved in sodium hydroxide
What happens when fehling’s solution is heated with an aldehyde?
The copper(II) ions are reduced to a brick-red precipitate of copper(I) oxide
What equation represent the colour change when reacting and aldehyde with Tollens’ reagent?
colourless Ag(NH3)2+ + e- —–> silver Ag + 2NH3
What equation represents the colour change when reacting an aldehyde with Fehling’s solution?
blue Cu2+ + e- —-> brick red Cu+
What is the only difference between benedicts solution and Fehling’s solution?
In Benedict’s solution the copper(II) ions are dissolved in sodium carbonate instead
If you heat an aldehyde with acidified dichromate(VI) ions, what do you get?
A carboxlic acid. The solution turns from orange to green
What is the colour change when you heat an aldehyde with acidified dichromate ions?
Orange to green
What can you reduce an aldehyde to?
A primary alcohol
What can you reduce a ketone to?
A secondary alcohol
When reducing aldehydes or ketones, what is the best reducing agent to use?
Lithium aluminium hydroxide
What is hydrogen cyanide? (HCN)
A weak acid, a highly toxic gas
When hydrogen cyanide reacts with carbonyl compounds what does it form?
Hydroxynitriles
What happens during the mechanism of the reaction between a carbonyl compound and hydrogen cyanide?
1-The CN- ions attacks the slightly +carbon atom and dontates a pair of electrons to it. Both electrons from the double bond transfer to the oxygen
2-H+ bonds to the water from the OH group forming a hydroxynitrile
Why is acidified potassium cyanide used instead of hydrogen cyanide in a labatory?
Hydrogen cyanide is a toxic gas
When a hydroxynitrile atom is being formed, how comee the groups surrounding the carbonyl atom in a ketone or aldehyde are planar?
The CN- ions can attack it from either side
When you react an aldehyde or an asymmetric ketone with CN-, what do you get?
A racemic mixture of 2 optical isomers
Why is a hydroxynitrile optically innactive?
It is a racemic mixture
When testing for a carbonyl group, what is 2,4-dinitrophenylhydrazine dissolved in?
Methanol and concentrated sulfuric acid
If a carbonyl is present, what does 2,4-dinitrophenylhydrazine react to form?
A bright orange precipitate
If a carbonyl is heated with iodine in the presence of an alkali and a yellow precipitate of triiodomethane is formed, what does this mean?
The carbonyl contains a methyl carbonyl group
If something contains a methyl carbonyl group, what must it be?
A ketone or ethanal
What are the reagents and conditions necessary to convert an aldehyde into an alcohol?
Mix with lithium aluminium hydride
What can you do with the orange precipitate that is formed when 2,4-dinitrophenylhydrazine is reacted with a carbonyl?
Measure the melting point and compare it to a known melting point to find out which carbonyl it is
What are the reagents and conditions necessary to convert a carbonyl into a hydroxynitrile?
React the carbonyl with hydrogen cyanide
What is the type of reaction when hydrogen cyanide reacts with carbonyl compounds?
Nucleophillic addition
What functional groups do carboxylic acids contain?
The carboxyl functional group, COOH
How do you name carboxylic acids?
Add -oic acid at the end of the longest carbon chain
As carboxylic acid is a weak acid, what does it do in water?
It partially dissocotiates to form carboxylate ions and H+ ions
Why do carboxylic acids have relatively high boiling points?
They form hydrogen bonds with each other
Why are carboxylic acids very soluble in water?
They can form hydrogen bonds with the water molecules
Why does the solubility of carboxylic acids decrease as the length of the carbon chain increases?
The hydrocarbon chains can’t form hydrogen bonds with the water but do disrupt the hydrogen bonds present between the water molecules, so large carboxylic acids can’t dissolve
In pure, liquid carboxylic acids, dimers can form. What does this mean?
The molecule hydrogen bonds with just one other molecule, increasing the size of the molecule and boiling point
How can a carboxylic acid be formed from an alcohol?
A primary alcoho, oxidises to form an aldehyde, which can then oxidise to form a carboxlic acid
What reagent is often uses to oxidise a primary alcohol to an alehyde and then to a carboxylic acid?
Acidified potassium dichromate
How can a carboxylic acid be made from hydrolysing a nitrile?
Reflux the nitrile with dilute HCl and then distil off the carboxylic acid
What are carboxylic acid neutralised by?
Aqueous bases to form salts and water
When carboxylic acids react with carbonates or hydrogen carbonates, what do they form?
A salt, carbon dioxide and water
When you react a carboxylic acid with a powerful reducing agent what can you form?
A primary alcohol
When you mix a carboxylic acid with phosphorous chloride, what can you form?
An acyl chloride
What is the ester functional group?
-COO-
What is the name of an ester made up of?
Two parts, the first bit comes from the alchol and the second bit from the carboxylic acid
What do esters end in?
-oate
Describe the process when naming an ester:
1-Look at the alkyl group that came from the alcohol 2-look at the part that came from the carboxylic acid(swap the -oic acid for -oate)
How are esters made?
From heating a carboxylic acid with an alcohol
What is esterification?
When you heat a carboxylic acid with an alcohol in the presence of an acid catalyst
What catalyst do you have to use during esterififcation?
An acid catalyst, such as concentrated H2SO4 or HCl
How do you make ethyl ethanoate?
You reflux ethanoic acid with ethanol and concentrated sulfic acid as the catalyst
When making ethyl ethanoate, why do you separate the product as it is formed?
The reaction is reversible
Why do you mix the prodcut of esterification with sodium carbonate?
To react with any carboxylic acid that might have snuck in. The ethyl ethanoate forms a layer on top can be easily separated with a separating funnel
When is ethyl ethanoate used?
As a solvent in chromatography and as a pineapple flavouring
What are the 2 ways inwhich esters can be broken up?
Acid hydrolysis and base hydrolysis
What does acid hydrolysis split the ester into?
An acid and an alcohol
How do you perform acid hydrolysis with an ester?
Reflux the ester with a dilute acid,such as HCl or H2SO4
What does base hydrolysis break up the ester into?
A carboxylate ion and an alcohol
How do you perform base hydrolysis?
Reflux the ester with a dilute base, such as sodiumhydroxide
What do diols contain?
2 -OH functional groups
What do dicarboxylic acids contain?
2 COOH functional groups
When dicarboxylic acids react with diols what do they form?
Long ester chains
What are long ester chains called?
Polyester chains
What are the main properties of polyester chains?
Strong, flexible and abrasion resistant
What is the functional group of acyl chlorides?
COCl
When naming acyl chlorides,what does their name end in?
-oyl chloride
What happens when acyl chlordies react with cold water?
A vigorous reaction producing a carboxylic acid
What happens when acyl chlorides react with alcohols?
vigorous reaction occurs and an ester is produced
What happens when acyl chlorides react with concentrated ammonia?
A violent reaction at room temperature, producing an amide
What is an amide functional group?
C0NH2
What happens when acyl chlorides react with amines?
A violent reaction at room temperature, producing an N-substituted amide
What do acyl chlordies easily lose?
Their chlorine atom
