Unit 2.6 Halogenoalkanes Flashcards
What is a halogenoalkane?
- A homologous series
- In which one/or more of the hydrogen atoms
- Have been replaced by a halogen
Explain a halogenoalkane undergoing an elimination reaction
Hydrogen halides are acidic ∴ can be removed using an alkali
Dissolving NaOH in ethanol will avoid a substitution reaction
(halogen replaced with an OH group - apparently that’s 2.5)
How do i show u 1-bromoprone converted into propene and hydrogen bromide
Meh, i’ll state the chemical formula ig?
C3H7Br + NaOH (in ethanol) -> C3H6 + HBr
From saturated to unsaturated
(do i needa know this?)
Show unsymmetrical halogenoalkanes forming into more than one product when undergoing an elimination reaction
Chemical formula state D:
Bro idk, if this is helpful lowkey, I’ll think about writing it ig (will forget)
What is a nucleophile?
Has an electron pair that can be donated to an electron deficient centre
How do C-X (carbon halogen bonds) able to undergo necleophilic attack?
- They’re polar and have a permanent dipole
- Electron-deficient carbons can undergo
- Nucleophilic attack leading to substitution
What should be included within nucleophilic substitution diagram?
- Lone pairs
- Dipoles
- Charges
- Curly arrows
How to draw nucleophilic substitution???
This is so bad….
- C2H5X (X = random halogen)
- Curly arrow from OH ion pointing towards the C connected to X
- Show O as lone pair within OH and the negative charge
- Show C has delta positive and X has delta negative - Show curly arrow from bond between C-X and X
- Results:
C2H5OH + X-
- Show X as lone pair with negative charge
Can u draw nucleophilic substitution for other halogenalkenes?
Heck yea
Describe the rate of nucleophilic substitution towards carbon-halogens
- Rate increases down the group
- The more reactive the halogen
- The stronger the bond
- The longer the reaction will take
Show me rates of reaction between 3 halogenoalkanes in terms of nucleophilic substitution
Slowest
RCl
RBr
RI
Fastest
How to test for halogenalkanes?
- Add water (hydrolysis)
- Add silver nitrate (AgNO3)
Draw mechanism for nucleophilic substitution of 1-chloroproane with water
Ehhhh, wait
How is the nucleophilic substitution with water very slow?
- Water not good nucleophile
- Lacks full negative charge [of, say, a hydroxide ion]
How would u speed up nucleophilic substitution with water?
Add sodium hydroxide (NaOH)
If u use sodium hydroxide for nucleophilic substitution, what should u also add and why?
Nitric acid, sodium hydroxide would interfere with the results of the test
Chlorine with Ag+?
White ppt
Bromide with Ag+
Cream ppt
Iodide with Ag+
Yellow ppt
Chlorine’s “ppt” with NH3
Ppt dissolves
Bromide’s “ppt” with NH3
Ppt dissolves **if concentrated NH3
Iodide’s “ppt” with NH3
No change
What are CFCs (chlorofluorocarbons)?
Halogenoalkane molecules where all of the hydrogen atoms have been replaced with fluorine and chlorine atoms
What were CFC’s used for?
- Refrigerants
- Propellants - aerosols
- Generating foamed plastics - expanded polystyrene/polyurethane foam
- Solves - dry cleaning
- General degreasing purposes
- Anaesthetics
How were CFCs dangerous?
Responsible for destroying ozone layer
- At high atmosphere, carbon-chlorine bonds break
- Gives chlorine free radicals
- They destroy ozone
- In addition, causes global warming
- Can cause skin cancer (should know why ¬.¬)
What are ozone holes?
Area of decreases concentration of ozone in ozone layer (particularly at the poles)
In addition, cuz cycle of ozone formation and decomposition absorbs medium and high energy UV radiation, decrease in ozone concentration causes more of this radiation to reach the surface of the earth
What can medium to high energy UV radiation cause?
- Sunburn
- Skin cancers
- Eye cataracts
- Decreased immune response
- Plant damage
- Polymer decomposition
What was the way of stopping ozone destruction by CFCs?
Prevent the releasing of the substances
Which is the main radical damaging the ozone in the atmosphere and why?
Chlorine Cl. radical from chlorine-carbon bond
It’s the weakest in a CFC
Easily broken by UV radiation
What’s the experiment to carry out nucleophilic substitution?
Reflux experiment
What is reflux?
Heating a reaction mixture to boiling. A process of evaporation and condensation
Describe reflux experiment
- Reaction mixture heated
- Liquids evaporate
- Vapour rises up through condenser
- Condenser has a cold-water jacket
- That’ll cool the vapour back to a liquid
- This’ll drip back into the reaction mixture
- A continuous process of evaporation and condensation will take place without loss of product
Course, there’s more for this yano of this “reflux experiment” so u be careful now
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