Summary
Summary Module 4.2.2 Chapter 15 Haloalkanes
- Course
- Institution
notes on: 1 - haloalkanes 2 - organo-halogen compounds in environment
[Show more]
Seller
Follow
saimabegum
Content preview
15.1 - Haloalkanesnaming - Primary = halogen - carbon 1 alkyl group
- Secondary – halogen – carbon + 2 alkyl groups
- Tertiary – halogen – carbon + 3 alkyl groups
reactivity - Haloalkanes have H + Halogen.
- Halogen is more electronegative than carbon atoms so e- pair in bond is closer to H atom = polar.
- Carbon is slightly +ve and can attract lone pair, species donating lone pair = nucleophiles.
- Nucleophiles – atom or group attracted e- deficient carbon to donate 2 e- to form covalent bond.
1) OH- (2 lone) 2) H2O (2 lone) 3)NH3 (2 lone)
- When haloalkane + nucleophile -> nucleophile replaces halogen = new func group (substitution)
Hydrolysis - Substitution = molecule being split into 2 products where halogen atom is replaced by OH-.
Nucleophilic 1)OH approaches opposite side of C atom with halogen. (arrow from OH with lone pairs and another arrow
substitution at C-halogen with delta charges)
2) direction minimises repulsion between OH and delta –ve halogen.
3) lone pair of e- on OH is attracted and donated to delta +ve atom.
4) new bond is formed between O in OH and C = C-halogen breaks by heterolytic fission -> alcohol + halide.
- Haloalkanes can be converted to alcohols with NaOH (aq) at room temp and is slow but heated
under reflux to obtain good yield.
- Carbon-halogen bond is broken and OH- group replaces halogen in haloalkane – rate of hydrolysis
depends on strength of bond.
- Graph with bond enthalpy;
1) lowest bond enthalpy = faster reaction
2) 3rd lowest = react faster than 2nd.
2) highest = unreactive as large amount of E required to overcome bond.
Measuring - Carried out in presence of AgNO3 – so halide ions are produced which react with Ag+ to form
rate of precipitate of silver halide.
hydrolysis - Nucleophile is present in AgNO3(aq) - usually H2O = haloalkanes insoluble in H2O = reaction carried
out in presence of ethanol solvent
- Ethanol = allows water and haloalkane to mix and produce one product.
1) 3 test tubes with 1cm3 of ethanol and 2 drops of haloalkane
2) stand the test tubes in water bath at 60C
3) Place test tube with 0.1mol dm-3 of AgNO3 in water bath and allow all tubes to reach a constant
temperature.
4) add 1cm3 of AgNO3 to each test tube and measure time taken for precipitate (max 5 mins)
- Has most precipitate = rate of hydrolysis increases as strength of carbon-halogen bond decreases.
- Least precipitate = slower rate = strongest = as more E required for precipitate to form.
Hydrolysis in - Primary = slowest rate of reaction
haloalkanes - Tertiary = fastest rate of reaction
- Due to reaction mechanism – primary reacts by 1 step but tertiary has 2 step
- 1st step = carbon – halogen bond of tertiary haloalkane breaks by heterolytic fission = tertiary
carbocation and halide ion
- 2nd step = OH ion attacks carbocation to form organic product
- Increased rate due to increased stability of tertiary carbocation > primary.
15.2 - Organo halogen compounds in environment
uses - Molecules with halogen in carbon chain – used in many pesticides.
- Rarely found in nature -> not easily broken down naturally in environment.
- General solvents, dry cleaning solvents, making polymers, flame retardants and refrigerants.
Ozone - Found at outer edge of stratosphere with make up of tiny fraction of gases – absorb biologically damaging
layer UV radiation from sun rays = only some pass through to earth.
- UV related to sunburn as it has harmful effects
- Continued depletion of ozone = more UV to pass through to earth = damaging to living organisms =
increase in genetic damage and risk of skin cancer.
- Ozone is continuously being formed and broken down by UV.
- O2 ->2O (using high energy UV to break into radicals)
- O2 + O -> O3 (O2 and radicals which ozone forms and breaks down where rate of form and break is same)
CFCs + - Human activity at CFC disrupts the equilibrium.
ozone - Was used as refrigerants due to being very stable because of its strength of C-halogen bond.
- CFCs remain stable until they reach the stratosphere - CFC break down forming Cl radicals which catalyse
breakdown of ozone layer
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller saimabegum. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $7.09. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
67474 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now