Alkanes/Haloalkanes Flashcards
Define Ozone
O3 in atmosphere - absorbs UV
Outline the danger of Holes in the Ozone
O3 decrease = increase UV & skin cancer
Define CFCs and outline their impact on Ozone
Chlorofluorocarbons - decrease in O3
Outline the 2 reactions of how CFCs reduce Ozone
- Cl* + O3 -> ClO* + O2
- ClO* + O3 -> Cl* + 2O2
Outline the overall reaction of CFC Ozone reduction
203 -> 3O2
Why is alkane combustion important?
Hi energy release
Outline Complete combustion
(Enough O2 present) X + O2 -> CO2 + H2O
Outline incomplete combustion
(Not enough O2) X+O2 -> CO+C+H2O
Outline the purpose of Catalytic converters
Removes CO & NOx (toxic)
Outline the process inside a catalytic converter
HC, CO, NOx (from air N2) + rhodium catalyst -> N2, H2O, CO2
Outline the danger of S impurities
H in H2O in atmosphere = H2SO4
What’s used in Flue Gas Desulfurisation?
CaO + gypsum
Identify the importance of Flue Gas Desulfurisation?
Pollutants -> global warming, H+ rain, health issues
Define Cracking
C-C-C-C-C-C -> C-C C-C C-C (more useful)
Outline the conditions and products of Thermal Cracking
Conditions: 1200K & 7000 kPa
Products: Mixture of CnH2n+2 & CnH2n
Outline the Conditions and Products of Catalytic Cracking
Conditions: 720K, Normal Pa, Zeolite catalyst
Products: Aromatic Compounds and C rings
Define Chlorination of Alkanes
Alkanes + Halogens ->(UV)-> Halogenoalkanes
Outline how Alkane Chlorination works
UV breaks down Halogen bonds -> Free Radicals & initiation, propagation & termination
Outline the Initiation in Chlorination (define and reaction)
Halogen broken down
Cl2 ->(UV)-> 2Cl*
Outline the 2 Propagation steps in Chlorination (define and both reactions)
H replaced and Cl* reformed as a catalyst
Cl* + CH4 -> *CH3 + HCl
CH3 + Cl2 -> CH3Cl + Cl
Outline the Termination step of Chlorination (define and 3 reactions)
2 free radicals join to form stable product
CH3 + CH3 -> C2H6
OR
Cl + * CH3 ->CH3Cl
OR
Cl + Cl -> Cl2
Define Fractional Distillation
Process used to separate hydrocarbons of different lengths from crude oil through different boiling points
Outline the 3 steps of Fractional Distillation
- Crude Oil vaporised
- Vapours rise, cool, condensed
- Proucts siphoned off
Outline how the hydrocarbons are separated when vapourised
Depends on boiling points
Long C Chain = condense low
Short C chain = condense high
Mushroom trays - collect can’t go back down
Define Haloalkane
Alkane bonded to Halogen atom(s)
Define Nucleophile
e- pair donor - attracted to areas of low e- density
Define Electrophile
e- pair acceptor - attracted to areas of hi e- density
Define Electronegativity
Ability 4 atom to attract e- in covalent bond
Outline the 3 types of Haloalkane
Primary = 2 or 3 H
Secondary = 1 H
Tertiary = No H
Outline the 3 physical properties of Haloalkanes
- C Chain increase=boiling point + VDW forces increase
- Down group 7 = boiling point increase
- If < room temp state is (g)
Outline the 3 factors affecting haloalkane boiling point
- C chain length (more VDW)
- Type of Halogen (more e-=stronger VDW)
- Primary, Secondary or Tertiary
Outline why there are permanent dipole forces in Haloalkanes
Electronegativity diff with C & Halogen
C is + dipole Halogen is - dipole
Outline the outlier to Haloalkane permanent dipoles
Iodine (so big)
Why don’t permanent dipoles impact the boiling points?
Due to increasing strength of VDW Forces the hi e- Number outweighs loss of permanent dipole
Outline the 3 types of Haloalkanes
Primary = 2/3 H
Secondary = 1 H
Tertiary = No H
Outline the trend in BP for the type of Haloalkane
Primary highest:
Closer together -> stronger VDW = more energy to break
Why are Haloalkanes only slightly soluble in water?
Must break VDWs & H bonds between H2O molecules
What does the reactivity of Haloalkanes depend on?
Bond length: C-F < C-Cl < C-Br < C-I
Bond strength: C-I < C-Br < C-Cl < C-F
Molecule size: F < Cl < Br < I
Define Nucleophilic substitution
Nucleophile replaces a group/atom in OG Molecule
Describe the general mechanism for Haloalkane Nucleophilic Substitution
1.-ve Nucleophile attacks Chiral C
2. C has 5 bonds 1 bond breaks
3. Halogen removed, becomes -
Outline the nucleophilic substitution of Haloalkanes with Hyrdoxide Ions
Haloalkanes + OH- boiled under reflux + (aq) NaOH/(aq) KOH
Forms alcohols
Describe the mechanism for Nucleophilic Substitution of Haloalkanes with Hydroxide Ions
OH- (nucleophile) attacks + dipole C from behind
Halogen leaves - becomes Halide ion
Outline the nucleophilic substitution of Haloalkanes with Cyanide Ions
Haloalkanes + CN- boiled under reflux + (aq) ethanol
Forms Nitriles
Outline the reaction for the nucleophilic substitution of Haloalkanes with Hydroxide ions.
R-X + OH- -> R-OH + X-
Outline the reaction for the nucleophilic substitution of Haloalkanes with Cyanide ions.
R-X + CN- -> R-CN + X-
Describe the mechanism for the nucleophilic substitution of Haloalkanes with Cyanide ions.
Same as Hydroxide ions
Outline the conditions of the nucleophilic substitution of ammonia and alkanes
Ethanolic ammonia in a sealed tube - primary amine formed
Outline the 4 steps of the nucleophilic substitution of ammonia and alkanes
- e- pair on NH3 attacks + dipole C
- NH3 must remove a H atom & Halide ion forms
- H atom forms +NH4 with another NH3 molecule
- +NH4 attracted to -Halide ion
Outline the 3 conditions for the elimination of Haloalkanes
- NaOH/KOH as a base
- No H2O present ethanol needed as a solvent
- Heat needed
Describe the mechanism of the elimination reaction of Haloalkanes
- :OH- attacks H atom on C adjacent to C atom with Halogen to form H2O
- H breaks off forming a C=C - Halogen atom breaks off = Halide ion
Outline how the type of halogenoalkane determines either an elimination or nucleophilic substitution
Primary = Nucleophilic Substitution
Secondary = Both
Tertiary = Elimination
