Organics 1 D-E

Question 1

whats a primary haloalkane

Answer 1

• when a halogen is attached to a carbon that itself is attached to one other alkyl group

Question 2

whats a secondary haloalkane

Answer 2

when a halogen is attached to a carbon that itself is attached to two other alkyl groups

Question 3

whats a tertiary haloalkane

Answer 3

when a halogen is attached to a carbon that itself is attached to three other alkyl groups

Question 4

trend in boiling points of haloalkane

Answer 4

1. As chain length increases boiling point increases due to:
   - More points of contact
   - Greater London forces
   - So more energy needed to break London forces
   
   2. Boiling points increase down group 7 (for same carbon chain):
      - Iodine has a lot more electrons so London forces are greater (more important than dipole interactions)

Question 5

solubility of haloalkanes

Answer 5

Insoluble in water:
- Intermolecular forces formed between water and halogenalkane aren’t strong enough so don’t release enough energy to break the hydrogen bonds between water molecules.
Soluble in organic solvents:
- We always dissolve in ethanol when carrying out reactions with aqueous reagents as alcohol dissolves both halogenalkane and water

Question 6

trend in bond polarity in haloalkanes

Answer 6

• electronegativity of halogens decrease as you go down the group
• carbon-flourine bond shorter than carbon-iodine/carbon-bromine bond because of its small ionic radius so bonding pair close to nucleus
• carbon-flourine bond more polar than carbon-iodine/carbon-bromine bond because of high electronegativity
• therefore as you go down the froup the haloalkanes become more reactive since they have a lower bond enthalpy

Question 7

formation of alcohols from haloalkanes with water

draw it out

Answer 7

• hydrolysis reaction
• water
• heated in a water bath
• haloalkane + H2O —> alcohol + H+ + X- (HX)
• slower/weaker reaction than with aqueous alkali since water is delta ngetave so is a weaker nucleophile compared to OH- ions havign a full negative charge

Question 8

what is a nucleophile

Answer 8

• Chemical species with a lone pair that are attracted to areas of positive charge
• need to have a full or partial negative charge
• bond with delta positive carbon atoms

Question 9

test for haloalkanes

Answer 9

• add silver nitrate solution (AgNO3)
• Ag+ ions will react with the halide ions to form a precipitate
• Ag+(aq) + Cl-(aq) -> AgCl(s) white precipitate
• Ag+(aq) + Br-(aq) -> AgBr(s) cream precipitate
• Ag+(aq) + I-(aq) -> AgI(s) yellow precipitate
  Cl - clean —> white, then gets more yellow
• Time taken for precipitate to appear can be used to determine relative rates of reaction - expect iodine to form precipitate first

Question 10

formation of nitriles from haloalkanes

draw it out

Answer 10

• nucleophilic substitution
• KCN
• ethanol + heated under reflux
• often used as intermediates to make another product with a longer carbon chain since provide an extra carbon increasing carbon chain length
• halogenoalkane + CN- —> nitrile + halogen

Question 11

formation of alcohols from haloalkanes with aqueos alkali

draw it out

Answer 11

• nucleophilic substitution
• 50/50 mixture of ethanol and water + aqueous alkali eg NaOH
• heat under reflux
  haloalkane + OH- —> alcohol + halogen

Question 12

formation of a secondary amine

draw it out

Answer 12

• when ethanolic ammonia not in excess
• also reflux and sealed container so ammonia gas does not escape
• prodcut from primary amine formation acts as nucleophile and the N is attracted ot the carbon of a hydrocarbon
• then a Hydrogen leaves an electrons accepted by the N
• results in secondary amine + H+ + X-

Question 12

formation of a primary amine

draw it out

Answer 12

• excess ethanolic amonnia
• reflux and sealed container so ammonia gas doesn’t escape
• ammonia acts as a nucleophile and is attracted to carbon and the halogen leaves and forms an ion —> forms an ion with N having a lil + and 3 hydrogens (my bad this doesn’t make sense like when u draw it out x)
• another amine comes along acting as a base and si attracted ot one of H off of the N, formign ammonium a halogen ion and a primary amine
  R-CH2X + 2NH3 —> X-CH2NH2 + NH4+ + X-

Question 13

formation of alkenes from haloalkanes

Answer 13

• elimination reaction
• ethanolic alkali (high conc of OH-)
• heated under reflux
• haloalkane + OH- —> alkene + h2o + halogen

Question 14

what does SN1/SN2 mean

Answer 14

s- substiution
n - nucleophilic
1 - reactant in the rate determining step
2 - 2 reactants in the rate determining step

Question 15

descirbe SN2 mechanism

Answer 15

• primary and secondary haloalkanes
• nucleophile is attracted to delta positive cabron
• attacks on side opposite halogen, so halogen is repeled
• halogen leves the haloalkane as a halogen ion
  when drawing tranistion state has dotted line and square brackets and -ve charge
  slower than sn1

Question 16

describe SN1 mechanism

Answer 16

• tertiary alcohol
• 1 reactant in rate determining reaction
• two-step reaction
• In the first step, the C-X bond breaks heterolytically and the halogen leaves the halogenoalkane as an X- ion - very slow
• frist reaction very slow because a smal proportion of haloalkane ionises, helped with a polar solvent
• forms a tertiary carbocation - trigonal planar shape so can attack above or below plane
• in 2nd step carbocation is attacked by nucleophile

Question 17

key facts abt sn1 and sn2 mechanisms

Answer 17

SN1 reactions are faster due to lower activation energy.

SN1 reactions occur with 3° halogenoalkanes due to the stability of the carbocation formed.

1° halogenoalkanes do not undergo SN1 reactions as 1° carbocations are unstable, so must react via the slower (higher activation energy) SN2 mechanism.

3° halogenoalkanes cannot undergo SN2 reactions due to the steric hindrance of the of the R groups.

1° halogenoalkanes have low steric hinderance and therefore can undergo SN2.

2° halogenoalkanes undergo a mixture of both SN1 and SN2 depending on a number of factors (nucleophile, stearic hindrance, carbocation stability, solvent, leaving group).

Question 18

describe chlorination

3°

Answer 18

R……………………………….R
R - C-OH + c.HCl -> R-C-Cl + H2O
R……………………………….R
sn1 mechanism
needs ot be shaken to react

Question 19

describe chlorination

1° and 2°

Answer 19

reagents: PCl5
conditions: room temperature
R-OH + PCl5 —> R- Cl + POCl3 + HCl
low ataom economy and HCl is toxic

Question 20

describe bromination

Answer 20

reagents: KBr + 50% c.H2SO4
conditions: warm
2 reactions going on at the same time
HBr formed in situ and once formed reacts wtin alcohol
Formation of HBr:
2KBr + H2SO4 —> 2HBr + K2SO4
Substiution of alcohol group:
R-OH + HBr —> R-Br + H2O

Question 21

describe iodination

Answer 21

reagents: red phosphorus + I2
conditions: heated under reflux
PI3 is formed in situ
Formation of PI3:
2P + 3I2 —> 2PI3
subsition of alcohol group:
3R-OH + PI3 —> 3R-I + H3PO3

Question 22

dehydration of alcoholos to alkenes

Answer 22

regeant: c.H3PO4
conditions: heat
R-OH -(c.H3PO4)-> R-C=C-R + H2O
H……………………………….H…H

Question 23

oxidation of primary alcohols

Answer 23

• form aldehydes which cna further be refluxed ot form carboxylic acid
• oxidinsign agent is K2Cr2O7

Question 24

how to form an aldehyde

Answer 24

- primary alcohol added to K2Cr2O7 and heated - use distilation apparatus - since aldehyde has a lower bp than the alcohol reactant it will evaporate first and then condense intot he leibig condensor and wil be collected as distilate - partial oxidation

Question 25

how to form a carboxylic acid

Answer 25

- set up for reflux - used ot prevent loss of any volatile substance, any products of oxidation remain in the reaction mixture, Products which boil off condense in the vertical condenser then return to the heating flask - place alcohol and acidified potassum dichromate into pear shaped flask and heat - full oxidation

Question 26

oxidation of secondary alcohol

Answer 26

- forms a ketone - set up for reflux - also uses acidfied potassium dichromate

Question 27

describe aparatus for distilation of aldehyde

Answer 27

- in a round-bottomed flask heat K2Cr2O7 and alcohol - heat using a heating mantle - add anti-bumping granules into round-bottomed flask to ensure the formation of small bubbles and allow for smooth boiling. - still head with stoppered thermometer opposite opening ot condensor - ue a leibig condensor to maintain a temperature gradient that gets cooler as the vapour flow down the condenser and ensures they are liquid by the bottom - collection od product from unsealed aparatus from delivery tube into flask/beaker

Question 28

describe aparatus for reflux of carboxylic acid

Answer 28

- in a pear shaped flask add aclohol and K2Cr2O7 - add anti-bumping granules into round-bottomed flask to ensure the formation of small bubbles and allow for smooth boiling - leibig condensor fill up from bottom - we prevent uneven filling of the condenser which would make cooling less efficient.

Question 29

colour change of K2Cr2O7

Answer 29

- when oxidised goes from orange to green in alcohol

Question 30

test for carboxylic acid

Answer 30

- pH - red or orange - calcium carbonate - effervesence - magnessium ribbon - effervesence

Question 31

test for aldehydes

Answer 31

fehling's solution and warm - red to blue preceipitate

Question 32

test for primary and secondary alochol

Answer 32

acidified potassium dichromate - orange to green

Question 33

explain why solubility decreases as alcohol increases

Answer 33

as chain length increases, the proportion of the alcohol that cannot form hydrogen bonds increases AKA the alkyl group gets longer. The alkyl group is non-polar and cannot form hydrogen bonds, so the longer it is, the less soluble the alcohol