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chemistry > Isomers And Carbonyls > Flashcards

Isomers And Carbonyls Flashcards

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1
Q

What is a stereoisomer

A

Isomers with the same structural formula but different spatial arrangements of atoms

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2
Q

When does optical isomerism occur

A

When a carbon atom has 4 different functional groups attached to it

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3
Q

What are enantiomers

A

2 compounds that are optical isomers of each other (non superimposeable mirror images )

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4
Q

How do optical isomers work

A

They have similar physical and chemical properties but they rotate plane polarised light by the same amount but in opposite directions

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5
Q

What is a race mate / racemic mixture

A

A mixture containing a 50/50 mixture of 2 enantiomers

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6
Q

Why are racemic mixtures not detected by polarimeters

A

They don’t rotate plane polarised light

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7
Q

How is a race mate formed

A

When a reactant or intermediate has a original planar group in the molecule and is approached from both sides by an attacking species

There is an equal chance of it being attacked from both sides so an equal amount of each enantiomer is formed

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8
Q

What are 2 reactions that form racemates

A

An unsymmetrical alkene with HBr in Electrophilic addition

Nucleiphilic addition of HCN to aldehydes and unsymmetrical ketones

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9
Q

What are crabonyls

A

Compounds with the C=O bond

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10
Q

Why are smaller carbonyl soluble in water

A

They can form hydrogen bonds with the water

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11
Q

Why do carbonyls not undergo addition reactions easily

How do they attract nuceliphiles

A

The C=O is strong

The bond is polarised as O is more electronegative than carbon

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12
Q

What do primary alcohols oxidise to

A

Aldehydes then carboxylic acids

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13
Q

What do secondary alcohols oxidise to

A

Ketones

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14
Q

What is the oxidising agent used to oxidise alcohols

A

Acidified potassium dichromate solution

Or potassium dichromate solution and dilute sulfuric acid

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15
Q

How do you test for aldehydes

A

Heat gently with tollens reagent and silver mirror forms

Heat gently with fehlongs solution and brick red precipitate forms

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16
Q

What is the reducing agent for reducing carbonyls

A

NaBH4

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17
Q

What are aldehydes reduced to

A

Primary alcohol

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18
Q

What are ketones reduced to

A

Secondary alcohols

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19
Q

What is the mechanism for reducing alcohols

A

Nucleophilic addition

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20
Q

What is another way carbonyls can be reduced

A

Catalytic hydrogenation
Using hydrogen and a nickel catalyst
At a high pressure

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21
Q

How are hydroxinitriels formed
What are the conditions
What is the mechanism

A

Reacting carbonyls with HCN ( dilute sukfiric acid and CN source )
Room temp and pressure
Nuecliphikic addition

22
Q

What type of acids are carboxylic acids in terms of strength (2)

A

They are weak acids as they only slightly dissociate in water

But they are strong enough to displace carbon dioxide from carbonates

23
Q

Why do carboxylic acids dissolve in water

A

They form hydrogen bonds with water molecules

24
Q

How do carboxylic acids differ in strength based on chain length

A

The alkyl groups are electron releasing, a bigger chain lengths makes it more negative and less stable
So acids are weaker as they get biggger

25
Q

How do carboxylic acid strength differ with halogens

A

They are electron withdrawing so it makes it less negative and more stable
So stronger

26
Q

How are carboxylic acids tested

A

React with Na/CO3 or aqueous NaHCo3 to form effervescence when Co/2 released

27
Q

What is the only carboxylic acid that can be oxidised nd why

A

Methanoic acid

Its structure effectively has an aldehyde group so it forms carbonic acid when oxidised (this can decompose to give oxygen )

28
Q

What is an esterification reaction

A

Carboxylic acid + alcohol -»> ester + water

29
Q

How are esters named

A

The anoate from the carboxylic acid
The eyl from alcohol

30
Q

What are 3 users of esters

A

Perfume
Flavourings
Plasticisers for polymers

31
Q

Why do esters not form hydrogen bonds

A

They are polar but don’t form hydrogen bonds because there in no hydrogen bonded to a highly electronegative atom

32
Q

What is the solubility of esters
What is their bp like

A

Almost insoluble in water
Lower bp than the hydrogen bonded carboxylic acid they come from

33
Q

How do plasticisers work

A

They allow polymer chains to move more easily which makes it more flexible

34
Q

How can esters be hydrolysised (2)

A

Either heating with an acid or with sodium hydroxide

35
Q

What are the reagents and conditions for hydrolysis of esters using an acid

A

Dilute hydrochloric acid
Heat under reflux

36
Q

What is formed when an ester is hydrolysed by acid

A

A carboxylic acid and an alcohol (opposite of esterification )

37
Q

What is the problem with hydrolysis by acid of esters

A

It is a reversible reaction that doesn’t give a good yield of products

38
Q

What are the regents and conditions for ester hydrolysis with sodium hydroxide

A

Dilute sodium hydroxide
Heat under reflux

39
Q

Why is the hydrolysis of esters with NaOH not reversible

A

The carboxylic salt produced is an anion of the carboxylic acid which is resistant to attack by weak nucleophiles like alcohols so the reaction is not reversible

40
Q

How do you convert the carboxylic acid salt to a carboxylic acid form

A

Add a strong acid

41
Q

What is glycerol used in and why

A

Cosmetics food and glues

It forms hydrogen bonds very easily and is readily soluble in water

42
Q

How so biodiesel formed

A

Vegetable like or fats reacting with methanol to form methyl esters (biodiesel ) and glycerol

43
Q

What is the difference between acyl chloride and carboxylic acids

A

They are much more reactive

44
Q

What do acyl chlorides form when reacting with water

A

A carboxylic acid and HcL

45
Q

What do acid anhydrides form when reacting with water

A

2 carboxylic acids

46
Q

What do acyl chloride form when reacting with alcohol

A

Ester + Hcl

47
Q

What do acid anhydrides form when reacting with alcohols

A

Ester + carboxylic acid

48
Q

What do acyl chlorides form when reacting with ammonia

What is an observation

A

Primary amide + NH4Cl

White smoke of NH4CL

49
Q

What do acid anhydrides form when reacting with ammonia

A

Primary amide + ammonium salt

50
Q

What does an acid andydride form when reacting with primary amine

A

N substituted amide

51
Q

What does acyl chloride form when reacting with primary amine

A

N substituted amide

52
Q

What is the mechanism called for the reaction of acyl chlorides and acid anhydrides

A

Nucleophilic Addition Elimination

chemistry (23 decks)

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