Chapter 15 Halo alkanes Flashcards
How to name halokalkanes
Same way you name alcohols, based on how many R groups it connected to
What property of haloalkanes makes it undergo a soecific type of reaction + what is that
Halokalkanes are always polar as a halogen is always more elcttonegative then carbon, meaning electron pair sits closer to halogen then carbin, making carbin partially positive
- as it is partially positive the carbon can attract a NUCLEOPHILE, and undergo nucleophilic SUBSTITUTION WITH IT
What is a nuclophile and give wxamples
Why arent like hydrogen halides nucleophiles?
If electriphile an electorn pair accwptor a nucleophile is an electron pair donator, and thus if it can give electrons it has to be neagtivish
- basically something polar / negative charge
- or if it has a lone pair
2) these tend to be electrophiles as acids and dissociate instead and become IONS
- hydoxide ions, water, amonia etc
What happens basically in nucleophilic substion
Nucleophile approaches and attacks hakoalkane oppsite the hakogen, so the repulsion between NEGATIVELY NUCLEOPHILE and PARTIALLY NEGATIVE halogen is minimised
2) bonds made and heterolytic fission, essentially halogen replcaed by nucleophile
Desciribe hydrolysis as nucleophilic substition
Adding water or a hydroxide ion in
1) hydroxide ion attacks opposite as lone pair attracted to carbon and lone pair donates electrons the partially positve carbon
2) bond is made between oxygen and this carbon
3) carbin halogen bojd heterolytically fissions so one is ion , halogen becomes iojn
4) this gives an alcohol from haloalkane
How is yield of hydorlisis of a haloalkane increased
Slow at, room tempertayre so heated under REFLUX to give good yield
What does rate of hydrolysis in these reactions depend on and how does this vary between halogens, what cinclusions can we male?
Rate of hydrolysis depends on the STRENTGH of halogen carbon bond —> the weaker, the easier it is to replace and so more rate
Strength of halogens based on emthwloy goes down lower group, thus iodo alkanes REACT FASTER THAN ALL, then broml more thwn chloro, chrloro than flouro but gluror unrescrive as lot more ENERGY NEEDED TO BREAK BOND
We can show this by doing silver nitrate
How can your prove bond enthalpies and effect on rate of hydrolysis?
If you react aqeuous silver nitrate with halokalen, the nucleophile is water in the aqeuos kixture, and then the product id alcohol and a halogen ion. Thod will then mix with silver to form a coloured precipate .
-if you monitor how quick it takes to reach a certain amount of precipate (judging by thickness of colour) then the quickest ine to appear will be the highest rwte of hydrolysis, but have tue lowest bknd enthalpy
How to physically do experiment ?
(What you need to mix halo with water)
Why water bath
What conclsuion
Halokalne is insoluble in water , so you need ETHANOL SOLVENT so thatbthey mix and produce one layer
1) add 1cm ethanol and 2 drops of different haloalken two three teet tubes
2) put them in water bath at 60
3) add decent amount of silver nitrate to a test tube and put that in water bath too. Waiti till all have same temp
4) then quickly add 1 cm of silver nitrate to each test tube and start clock
5) measure how quick it took for “precipatet to appear” the quicker preicpate appears means more was made means rate if hydrolysis was faster snd results can be xplained usijg enthwlpy theory
- water bath ensures good rate of resctionn
Made faster = lower bond entalhy,
Rate of hydrolysisnincreases as strentgh of bind decreaes
What is an organohalogen
Molecules that containnat least one halogen atom joined to a carbon chain
What is oxone layer and why it protects us, what is concern
- ozone layer is found outer staosphere
Ozone layer only contains a specific amount of ozone , but this is enough ti absorob damaging uv rays (uv-b), whicnlined ti sunburn cancer
Depletion if oxone poses risk to increased risk of these like genetic dwmage etc
How is oxone formed at oxone layer
What basic effect of a chlorofluorocarbon and human activity
Uv rays break oxygen molecules into oxygen radicals
These then set in a steady state of EQUILIBRIUM with more oxygen molecules to make a reversible reaction
O2 + o- —> is o3 reverisble
2) human sctivity and cfcs have upset DELICATE EQUILIBRIUM
What are CFCS,
what used fir and
why were they used
However what did scientists discover
CHLOROFLUOROCARBONS and HCFCs were the most common compounds used as REFIGERANTS (something to cool temp) , and PROPELLANTS in aerosols
- this was because they were very stable due to carbon halogen bond
2) however scientists discovered these are only stable until they reach stratosphere, where they BEGIN TO BREAK DOWN , forming chlorine radicals, which CATALYSE breakdown of oxone layer
What did scientists discover ablut the strength of cfcs as they rise, and what effect did this have
2) however scientists discovered these are only stable until they reach stratosphere, where they BEGIN TO BREAK DOWN , forming chlorine radicals, which CATALYSE breakdown of oxone layer , reducing the amount if uv that can be absorbed as ozone is broken faster
How do CFCs break dkwn ozoje full mechanism
2) what can chlorine radical do at end 😭
Radical subsitituion involving initiation and two propagation
1) CFCS take years ti get stratosphere but once they there energy from uv radiation breaks a halogen carbin bond, as carbin - chlroine is least string (rememeber graph) this breaks , giving homolytic fission and thus TWO RADICALS .
2) a Cl- reacts with O3 —> clo- and o2
Then cl0- reacts with o- —> cl- and O2
Overall reaction is O3 +O- —> 2O2
This shows breakdown of ozone layer
2) the chlorine radical made in step two can now be used in another reaction = chain cussing a lot to break
