Topic 10 & 20 - Organic chemistry Flashcards

Question

What happens in the propagation process in the reaction mechanism?

Answer 1

- Free radicals are used and produced, allowing the reaction to continue (chain reaction)

Answer 2

- Free radicals are removed from the mixture by reacting them together and pair up electrons

Answer 3

A reaction in which a double bond is broken to add two hydrogens to a compound.

Answer 4

- Called hydrogenation - Alkene goes through addition reaction - Nickel catalyst and at 150°C CH₃CHCH₂ + H₂ → CH₃CH₂CH₃

Answer 5

- Forms dihalogeno compounds - Happen quickly at room temperature - Loss of colour of the halogen CH₃CHCH₂ + Br₂ → CH₃CHBrCH₂Br

Answer 6

- Form halogenoalkanes - React rapidly at room temperature CH₂CH₂ + HCl → CH₃CH₂Cl

Answer 7

- Called hydration - Converts the alkene into an alcohol - Involves an intermediate - Heat with steam and catalyst of concentrated H₂SO₄ CH₂CH₂ → CH₃CH₂(HSO₄) → CH₃CH₂OH + H₂SO₄ ^{H₂SO₄ catalyst} ^H₂O

Answer 8

- Alkene mixed together with bromine water forms a clear compound, the brown colour disappears - Alkane mixed with bromine water stays brown coloured

Answer 9

–(–CH₂–CH₂–)_n–

Answer 10

1. Polyethene 2. Polychrloroethene 3. Polypropene

Answer 11

The double bond of alkanes is broken down and many alkane molecules are put together in a long chain

Answer 12

- Hydrogenation is used to manufacture margarines from oils - Hydration is used to form ethanol - Polymerisation is used to form plastics

Answer 13

- Burns to produce CO₂ and water 2 CH₂OH(l) + 3 O₂(g) → 2 CO₂(g) + 4 H₂O(g)

Answer 14

First aldehydes and if further oxidised, carboxylic acid

Answer 15

By distilling the product off as it forms

Answer 16

By heating it under reflux

Answer 17

An electron-rich species that is attracted to parts of molecules that are electron deficient

Answer 18

Saturated alkanes that contain an atom of fluorine, chlorine, bromine, or iodine bonded to the carbon skeleton

Answer 19

An atom in a polar covalent bond which loses its electrons to a more electronegative atom

Answer 20

Breaking a bond where both the shared electrons go to one of the products. Two oppositely charged ions are produced: X:X → X⁺ + X:^–

Answer 21

Representing the motion of an electron pair: the tail of the arrow shows there the pair comes from and the head shows where it is going

Answer 22

The nucleophile used to replace the halogen

Answer 23

- For primary halogenoalkanes - The carbon atom is relatively open to attack by the nucleophile - An unstable transition state is formed in which the carbon is weakly bonded to both the halogen and the nucleophile - The carbon-halogen bond then breaks heterolytically, releasing Cl^– and forming the alcohol product CH₃Cl + OH^– → CH₃OH + Cl^–

Answer 24

The concentration of both the halogenoalkane and the hydroxide ion (bimolecular reaction)

Answer 25

- Tertiary halogenoalkanes - Three alkyl groups make it difficult for the nucleophile to attack the carbon atom - The first step involves the halogenoalkane ionising by breaking its carbon-halogen bond heterolytically - The carbon atom has a temporary positive charge (carbocation) - The carbocation is attacked by the nucleophile, forming a new bond - The alkyl groups have an electron-donating (positive inductive) effect which make the carbocation stable for long enough for the new bond to form CH₃C(CH₃)ClCH₃ + OH^– → CH₃C(CH₃)OHCH₃ + Cl^–

Answer 26

A mixture of both S_N1 and S_N2 mechanisms

Answer 27

\* = mechanism required red arrow = oxidation purple = reduction/addition of H₂ green = substitution yellow = addition grey = elimination blue = condensation

Answer 28

Because OH^– has a negative charge, H₂O doesn't

Answer 29

1. The class of the halogenoalkane - Tertiary is the fastest and primary the slowest 2. The identity of the halogen - Rate increases down Group 7 from the fluoroalkane to the iodoalkane

Answer 30

- NH₃ is a nucleophile due to the lone pair of electrons on the nitrogen atom - S_N2 - The substitution reaction yields in an amine: C₂H₅Br + NH₃ → C₂H₅NH₂ + HBr CH₃CHBrCH₃+ NH₃ → CH₃CH(NH₂)CH₃ + HBr (CH₃)₃CBr + NH₃ → (CH₃)₃CNH₂ + HBr - Amines can further behave as nucleophiles

Answer 31

- CN ion is a nucleophile as it contains a lone pair and a negative charge on the carbon - S_N2 - The substitution yields in a nitrile compound C₂H₅Br + KCN → C₂H₅CN + KBr

Answer 32

- Introduction of the nitrile group is an easy way to increase the length of the carbon chain in a molecule - Reduction occurs using hydrogen and nickel catalyst - Nitrile is converted into a primary amine C₂H₅CN + 2 H₂ → C₂H₅CH₂NH₂ - Nitriles are very useful intermediates (reaction pathways)

Answer 33

A reaction in which a small molecule is removed from a larger molecule, leading to the formation of an unsaturated product

Answer 34

A carbon–carbon double bond

Answer 35

CH₃CH₂CH₂Br + NaOH → CH₃CH=CH₂ + NaBr + H₂O - A hot alcoholic solvent is used

Answer 36

E2 (elimination bimolecular) E1 (elimination unimolecular)

Answer 37

- One-step mechanism - Bimolecular - OH^– ion acts as a base and accepts a proton, from the molecule - The carbon–bromine bond breaks heterolytically, electrons going to the bromide ion - The electrons from the carbon–hydrogen bond form the new bond of the double bond

Answer 38

- Unimolecular - Two-step process - (1) Ionisation of the halogenoalkane - (2) Formation of the double bond - Rate-determining step depends on the concentration of the halogenoalkane

Answer 39

Food flavourings and perfumes (also plasticisers to make plastics more flexible)

Answer 40

Two molecules react to form a product with the loss of a small molecule (formation of polymers)

Answer 41

Each reactant must have a functional group that reacts with the functional group on the other molecule

Answer 42

carboxylic acid + alcohol ⇔ ester water CH₃COOH + CH₃OH ⇔ CH₃COOCH₃ + H₂O - Esterification occurs - Formed by warming a mixture of the carboxylic acid and alcohol in the presence of concentrated sulfuric acid - The sulfuric acid acts as a catalyst and may also improve the yield

Answer 43

- They do not have free –OH groups so they cannot form hydrogen bonds - They are more volatile and less soluble in water

Answer 44

carboxylic acid + primary amine → secondary amide + water CH₃COOH + CH₃NH₂ → CH₃CONH(CH₃) + H₂O - Secondary amines react to form tertiary amides

Answer 45

- When the acid has two –COOH groups and the alcohol two –OH groups - The chain extends in both directions forming a polyester

Answer 46

- Condensation reaction of two amino acids - An amide link (peptide bond) is formed between the acids - A free –NH₂ group on one end and a free –COOH gorup on the other allow the continuing the reaction by condensation to form polypeptides and ultimately proteins

Answer 47

Esters - Used as food flavourings and perfumes - Used as plasticisers, helping to soften plastics and make them more flexible - Naturally occurring fats and oils are examples of esters (product of glycerol and fatty acids) - PET is used in synthetic fibres and the production of plastic bottles Polyamides - Polypeptides form proteins - Synthetic polyamides include plastics such as nylon and kevlar, used in clothing, carpets, machine parts, tyre cords, ropes

Answer 48

Compounds with the same structural formula but with different arrangement of atoms in space

Answer 49

- Called geometric isomers (cis-trans isomers) - Restricted free rotation of the bonded groups (double bond) - Cis = same side - Trans = opposite sides

Answer 50

Cis-trans isomers

Answer 51

1. Polarity of the molecules 2. The shape or symmetry of the molecules

Answer 52

- Affects the boiling points as it determines the strength of the intermolecular forces

Answer 53

- Affects the melting point as it affects the packing in the solid state - Trans-isomers are able to pack more closely due to their greater symmetry → the melting point is higher

Answer 54

- Generally very similar - Exception is butenedioic acid: - when cis-isomer is heated it condenses - when trans-isomer is heated it sublimes but no chemical change occurs

Answer 55

Cyclic molecules - Cyclopropane and cyclobutane - The substituted groups do not have to be on adjacent carbon atoms - The ring prevents rotation around the carbon atoms Dichloro derivatives:

Answer 56

A carbon that is bonded to four different atoms or groups to form a tetrahedral, or a molecule with such arrangement

Answer 57

The two isomers of molecules that show optical isomerism

Answer 58

A mixture that contains equal amounts of both enantiomers

Answer 59

Molecules that have no plane of symmetry and do not line up when put on top of each other

Answer 60

1. butan-2-ol 2. 2-chlorobutane

Answer 61

Isomers have identical physical and chemical properties with two exceptions: 1. Optical activity 2. Reactivity with other chiral molecules

Answer 62

Optical isomers' property of polarising light.

Answer 63

- When a beam of plane-polarised light passes through a solution of optical isomers, they rotate the plane of polarisation 1. The sample of isomers is placed in the sample tube 2. Plane-polarised light is passed through the sample tube 3. Rotation of the polarisation plane occurs in the tube 4. The light passes through a second polariser called the analyser 5. The analyser has been rotated until the light passes through it 6. The extent and direction of rotation brought about by the sample can be deduced from the analyser - Enantiomers of the same concentration rotate plane-polarised light in equal amounts but in opposite directions - A racemic mixture does not rotate the light because the enantiomers cancel out and the solution is said to be optically inactive

Answer 64

A method of separating two enantiomers from a racemic mixture by reacting them with another chiral compound

Answer 65

- The enantiomers produce two different products - Products have distinct chemical and physical properties and can be separated easily