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Flashcards in Haloalkanes Deck (13)
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Define haloalkane

Alkene molecules where one or more hydrogen atom has been replaced by a halogen atom


How do haloalkanes break by homolytic fission

High energy UV breaks the C-Hal bond Process occurs when the haloalkane reaches the stratosphere


Process of nucleophilic substitution with haloalkanes

δ+ on carbon attracts nucleophiles Nucleophiles forms bond to the δ+ carbon Carbon-halogen bond breaks Example of substitution reaction


Define nucleophile

Species with a lone pair of electrons which it donates to a δ+ carbon forming a new covalent bond


Define substitution reactions

Where one atom or group in a molecule gets replaced by another atom or group


Describe the haloalkane reaction with water via nucleophilic substitution

Water —> nucleophile due to lone pair on oxygen and is δ- (not full negative charge) Reflux


Describe the haloalkane reaction with ammonia via nucleophilic substitution + reagents and conditions

Ammonia —> nucleophile due to lone pair and δ- charge R+C —> cAmmonia solution & heat in sealed tube


Describe the process of making a haloalkane via nucleophilic substitution + reagents and conditions

Use alcohol OH (lone pair) bonds with H+ to make +OH2 C-OH2+ bond breaks Nucleophile (halogen) bonds to carbon Product is water R+C —> concentrated hydrogen halide


Two factors that affect reactivity of haloalkane

Polarity of carbon-halogen bond Bond strength of carbon- halogen bond


Why does the polarity of the carbon-halogen bond matter in terms of reactivity

C-halogen bond becomes less electronegative as you go down the group Making the carbon less δ+ —> nucleophiles slower to attack


Why does the bond strength of the carbon-halogen bond matter in terms of reactivity

Bond enthalpy of C-halogen bond decreases going down the group Larger halogen atom —> further away bonding electrons from nucleus so weaker attraction Nucleophile can attack easier when bond enthalpy decreases as the bond has to break


Describe a practical method to check the reactivity of haloalkanes

Add chloroalkane, bromoalkane & iodoalkane to three distinct tubes To each add silver nitrate & ethanol as solvent PPT of silver halide forms The fastest PPT that forms will be most reactive


Difficult example; nucleophilic substitution when vanillin reacts with cyanide ions and dilute acid

Lone pair on cyanide bonds C=O

H+ bonds to O-