Haloalkanes Flashcards
(9 cards)
What is the general formula for haloalkanes and how are they named?
CnH2n+1X
Fluoro-
Chloro-
Bromo-
Iodo-
Whats the reactivity of haloalkanes based of electronegativity?
Halogen atom is more electronegative than the carbon atom so the bonded pair of electrons is attracted more towards the halogen atom, resulting in a polar bond between carbon - halogen. The electronegativity decreases down the group resulting in decrease in polarity.
The polar bond results in carbon being electron deficient so attracts nucleophiles.
What is a nucleophile and whats the mechanism called when haloalkanes react with nucleophile?
Nucleophile is an electron pair donor.
Nucleophilic substitution reaction
What is the reaction of haloalkanes in hydrolysis ?
Hydrolysis example of nucelophillic substitution reaction.
Reagents: water or any aqueous hydroxide (OH- ions source)
Conditions: ethanol solvent and heat under reflux (reflux is continuous boiling/condensing of reaction mixture to ensure reaction takes place but prevents contents of flask boiling dry.)
An alcohol is formed.
What is nucelophillic substitution reaction?
In nucleophilic substitution reactions an atom or group of atoms is replaced by an electron pair donor.
The carbon-halogen bond breaks by heterolytic fission and halide ion is formed.
Haloalkane —> alcohol + halide ion
How do you measure the rate of hydrolysis of primary haloalkanes?
Heat the haloalkane with aq silver nitrate(test for halide ions) in the presence of an ethanol solvent.
As reaction occurs, halide ion release from haloalkane reacts with aq silver nitrate forming a precipitate.
How is the rate of a hydrolysis reaction of haloalkanes influenced?
Rate of reaction is influenced by the strength of the carbon-halogen bond. The stronger the carbon-halogen bond, the slower the rate of reaction.
Fluorine-carbon bond strongest so requires more energy to break so is the slowest.
Carbon - iodine bond weakest so requires less energy to break so is the fastest.
As go down group, rate of hydrolysis increases.
What are the uses of haloalkanes?
They are non toxic, unreactive and have low volatility. CFC’s (chlorofluorocarbons) used as deodorants, refrigerants.
How do CFCs affect the environment?
Thin ozone layer. CFCs very stable and once react the stratosphere, they can split into radicals which react with ozone. They do this as UV radiation provides energy to break carbon-halogen bond so in presence of uv radiation, CFCs break down to form radicals by Homolytic fission.C-Cl bond has lowest bond enthalpy so breaks easier than C-F.
CF2Cl2 —> CF2Cl’ + Cl’
