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Chemistry A2- new > Unit 4- Further organic chemistry > Flashcards

Unit 4- Further organic chemistry Flashcards

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1
Q

What are the two forms of stereoisomerism?

A

geometric and optical isomers

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2
Q

what are geometric isomers?

A

isomers which have the same gruop of atoms but in a different spatial arrangement

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3
Q

How does geometric isomer occur?

A

due to the lack of rotation by the carbon carbon double bond

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4
Q

What is chirality?

A

when two objects are non superimposable and are mirror images of eachother, they are chiral. This feature is exclusive to asymmetrical objects

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5
Q

How is a molecule chiral?

A

if there are four different groups attached to a central carbon where the molecules are non superimposable and are mirror images

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6
Q

If the isomers are mirror images of eachother, what are they reffered to as?

A

enantiomers

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7
Q

How to tell between two enantiomers?

A

different effect on plane of polarised light where one enantiomer rotates the plane of light clockwise while the other anticlockwise

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8
Q

What type of wave is the plane of polarised light?

A

transverse

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9
Q

When an enantiomer is placed between two polaroids, what happens?

A

the second polaroid must be rotated to allow the light to pass through, this is the angle of rotation

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10
Q

What mixtures have no effect on the plane polarised light?

A

racemic mixtures

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11
Q

why do racemic mixtures have no effect on plane polarised light?

A

they are formed in a 1:1 ratio therefore the clockwise rotation is cancelled by the anticlockwise rotation

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12
Q

What is the functional group of an aldehyde?

A

a bonded hydrogen atom and a double bonded oxygen atom to a carbon atom

H-C=O

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13
Q

What is the functional group of a ketone?

A

A double bonded oxygen atom to a carbon

-C=O

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14
Q

what is the C=O functional group referred to as?

A

a carbonyl group

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15
Q

what are the properties of the carbonyl group?

A
  • greater boiling and melting temperature in comparison to alkanes but lower than alcohol
  • straight chain isomers are more packed therefore stronger than branched chain
  • aldehydes are slightly more volatile than ketones
  • aldehydes and ketones are miscible with water but this decreases as chain length increases
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16
Q

Why are aldehydes and ketones soluble in water?

A

Due to the ability to hydrogen bond with water

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17
Q

What are the effects of a carbonyl group?

A
  • pi and sigma bonds present
  • the bond is permanently polarised
  • cannot hydrogen bond between themselves
  • permament dipole-dipole interactions
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18
Q

Describe the oxidation reaction of aldehydes and ketones

A
  • aldehydes oxidise due to the hydrogen atom
  • oxidises to carboxylic acid
  • warming with potassium dichromate (VI) acidified with sulfuric acid
  • ketone does not readily oxidise
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19
Q

Describe the reaction with fehlings and benedicts

A
  • If an aldehyde is warmed, it is oxidised to a carboxylic acid
  • This reduces the fehlings giving a red-brown precipirate
  • precipitate is of copper(I) oxide
  • ketone does not react
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20
Q

How is tollens reagent formed?

A
  • produced by dissolving nitrate in water and adding aqeuous ammonia
  • silver (I) oxide is formed but dissolves as more ammonia is added
  • forms the complex diammine silver (I) ion
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21
Q

Describe the reaction with tollens reagent

A
  • Tollen is warmed gently with aldehyde
  • the aldehyde is oxidised
  • silver (I) ions are reduced forming silver metal
  • produces a silver mirror
  • ketone does not react
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22
Q

What are the oxidation reactions of aldehydes and ketones?

A
  • oxidation by potassium dichromate (VI)
  • With fehlings and benedicts
  • With tollens reagent
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23
Q

What is the reduction reaction of aldehydes and ketones?

A
  • aldehydes can be redcued to primary alcohols
  • ketones can be reduced to secondary alcohols
  • Lithium tetrahydridoalumate (LiAlH4) dissolved in dry ether can be used
  • sodium tetrahydridoborate (NaBH4) dissolved in ethanol can be used
24
Q

What is the addition reaction of aldehydes and ketones?

A
  • addition reaction with hydrogen cyanide (HCN)
  • produces hydroxynitriles
  • occurs in presence of cold alkali and potassium cyanide
  • the equilibrium K+ + CN- + H2O à K+ + HCN + OH- is formed
25
Q

What are the steps of the addition of hydrogen nitrile to an aldehyde or ketone?

A
  • Nucleophile CN- attacks the central carbon displacing a pair of electrons in the double bond and pushing the elctrons to the oxygen atom
  • negatively charged oxygen acts as a base and gains a proton
26
Q

What is the reaction between DNPH and aldehydes and carboxylic acids?

A
  • Reacts with bradys reagent to form a yellow/orange/red solid
  • DNPH (Bradys) is oringally a red-orange solid
  • condensation reaction
  • forms DNPH derivatives
27
Q

How are the DNPH derivatives used to identify a ketone or aldehydes?

A

different boiling and melting temerature specific to the aldehyde or ketone it is formed for

28
Q

Why is DNPH used?

A

DNPH derivatives are less soluble therefore crystallise easier

29
Q

Describe the reaction for iodine in the presence of alkali with aldehydes and ketones

A
  • aldehyde is warmed with iodine in alkaline
  • aldehyde reacts with iodine to form triodoethanal
  • triodoethanal reacts with alkali to form triodomethane
  • triodometahne (iodoform) is an insolbule yellow solid with a characteristic smell
30
Q

What is the functional group of a carboxylic acid?

A

-COOH where there is a OH bonded and a double bonded oxygen to a carbon

31
Q

What is a COOH group called?

A

carboxyl group

32
Q

What are the two factors which affect the properties of carboxylic acids?

A

polarity of the carboxyl group and the length of the carbon chain

33
Q

As the carbon chain length increases in carboxylic acid increases, what happens to the caroxyl group?

A

the effect is decreased

34
Q

What are the properties of carboxylic acids?

A
  • due to two polarised groups, relatively strong intermolecular forces are present leading to a high boiling and melting temperature
  • can exist as hydrogen bonded dimers thus increasing the boiling and melting temperature
  • small chain carboxylic acids soluble in water due to hydrogen bonding
35
Q

What are the two methods to produce carboxylic acids?

A
  • oxidation
  • hydrolysis of a nitrile
36
Q

How to produce a carboxylic acid by hydrolysis?

A
  • boil with dilute acid
  • CH3CH2CN + 2H2O + H+ –> CH3CH2COOH + NH4+
37
Q

What are the reactions carboxylic acids can undergo?

A
  • reduction
  • neutralisation
  • with phosphorus pentachloride
  • with alcohol
38
Q

Describe the reduction of carboxylic acids

A
  • can be reduced to a primary alcohol only
  • LiAlH4 in dry ether can be used
  • addition of water destroys any excess LiAlH4
  • water produced
39
Q

Describe the neutralisation of carboxylic acids

A
  • Reacts with a base
  • Forms a salt and water
  • salt formed is ionic and soluble
  • e.g. CH3COOH + NaOH –> CH3COO- Na+ + H2O
40
Q

How can carboxylic acids undergo neutralisation reactions?

A
  • carboyxlic acids dissociates in water
  • forms carboxylate ions and hydrogen ions
  • acts as an acid
41
Q

Describe the reaction with phosphorus pentachloride

A
  • reacts with solid phosphorus pentachloride (PCl5)
  • Forms an acyl chloride
  • Forms white fumes of hdyrogen chloride
  • Can be used to test for -OH
  • e.g. CH3COOH + PCl5 –> CH3COCl + POCl3 + HCl
42
Q

What is formed in the reaction between carboxylic acids and alcohols?

A

Esters (esterification)

43
Q

Describe the reaction between a carboxylic acid and water

A
  • presence of a strong acid catalyst
  • forms water as a product
  • can also be prepared using an acyl chloride and acid anhydride
44
Q

What are the two derivatives of carboxylic acids?

A
  • acyl chlorides
  • esters
45
Q

what is the functional group for an ester?

A

a C-O-C bond joining the alcohol and carboxylic acid

46
Q

What is the functional group for an acyl chloride?

A

A double bonded oxygen and a chlorine atom bonded to a carbon

47
Q

What are the reactions acyl chlorides undergo?

A
  • With water
  • With alcohol
  • With concentrated ammonia
  • With amines
48
Q

Describe the reaction between an acyl chloride and water

A
  • hydrolysed rapidly in cold water
  • hydrogen chloride fumes released
  • forms a carboxylic acid
49
Q

Describe the reaction between an acyl chloride and an alcohol

A
  • Forms an ester
  • takes place upon mixing without heating
  • forms hydrogen chloride
50
Q

Describe the reaction between acyl chlorides and concentrated ammonia

A
  • produces amides
  • upon mixing without heating
  • produces HCl where this reacts further
  • HCl + NH3 –> NH4Cl
51
Q

describe the reaction between acyl chlorides and amines?

A

forms a substituted amide

52
Q

What is a hydrolysis reaction regarding an ester?

A

when the ester splits up into a carboxylic acid and alcohol with water being used

53
Q

Describe the base hdyrolysis of esters

A
  • hydrolysed by boiling with potassium hydroxide solution
  • can be called saponification
  • when the acid is released, neutralised by the alkali to form a potassium salt
  • Ethyl ethanoate + OH- à ethanoate ion + ethanol
54
Q

Describe the acid hydrolysis of esters

A
  • Boiled with water and a dilute acid is used
  • provdes hydrogen ions which catalyses the reaction
  • Ethyl ethanoate + water à ethanoic acid + ethanol
55
Q

What is a condensation polymer?

A

when dicarboxylic acids and a diol react forming a polymer with water also being formed

56
Q

what can the polymers be used for?

A

plastic bottle drinks

Chemistry A2- new (4 decks)

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