2.6 Halogenoalkanes Flashcards
(15 cards)
why are halogenoalkanes polar? what are their deltas? What does this mean?
since they’re more electronegative than carbon
halogen = delta -
carbon = delta +
means the C is electron deficient and therefore susceptible to nucleophilic attack
summarise the reaction of halogenoalkanes with sodium hydroxide (aq)
reagents: halogenoalkane + NaOH + heat under reflux
mechanism: nucleophilic substitution
gen equation: CH3Cl + OH- -> CH3OH + Cl-
why is aqeous sodium hydroxide used rather than in ethanol?
bc halogenoalkane and sodium hydroxide in ethanol solvent makes alkene (dehydrogenation/elimination)
what is the effect of changing halogen in the reaction with aq sodium hydroxide? which is the most polar? why is C-Cl the strongest? what do these two factors mean together?
hydrolysis occurs at different rates
C-Cl most polar as Cl is most electronegative
Cl is the smallest halogen so C-Cl is the strongest
These two factors act in opposite directions and therefore iodo compound is hydrolysed the quickest therefore bond strength outweighs the effect of the charge on C
What is the general equation for testing for the presence of a halogen in an organic compound?
RX + NaOH (aq) -> ROH + Na + X-(aq)
what is the method for testing for the presence of a halogen in an organic compound
- place 5 drops of NaOH in a test tube and add 10 drops of X
- add a few drops for nitric acid
- Add about 8 drops of silver nitrate
when testing for the presence of a halogen, what are the positive tests? what do they do in NH3?
Cl = white ppt, dissolves in dilute NH3
Br = cream ppt, dissolves in conc NH3
I = yellow ppt, doesn’t dissolve in NH3
What is the mneumonic to remember the tests for halogenoalkanes?
Cookies with banging cream is yummy
Chlorine white bromine cream iodine yellow
What are some of the uses of halogenoalkanes?
- as solvents
- as anesthetics
- as refrigerants
why are halogenoalkanes used as solvents/effective degreasing agents?
bc they’re insoluble in water but able to mix w/a variety of non-polar/polar organic substance and is therefore effective degreasing agents
Why are halogenoalkanes used as refrigerants?
presence of permanent dipole-dipole means that boiling temps are close to room temp and therefore liquids can be easily evaporated or gas easily liquified
what are CFC’s most commonly used for?
for refrigerants and propellants in spray can
why are the use of CFC’s now tightly regulated?
bc of their toxicity and adverse effects in the upper atmosphere as holes in the ozone layer are thought to be caused by CFC’s, these allow UV light to reach earth’s surface and cause skin cancer
why are HFC’s replacement suggestions?
due to the problems of ozone depletion replacement suggestions are HFC’s bc they don’t contain C-Cl bond and cannot give Cl radicals
draw a reflux apparatus
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