Halogenoalkanes
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define primary halogenoalkane
the carbon atom which carries the halogen atom is only attached to one other alkyl group
define secondary halogenoalkane
the carbon atom which carries the halogen atom is attached directly to two alkyl groups
define tertiary halogenoalkane
the carbon atom which carried the halogen atom is attached directly to three alkyl groups
define nucleophile
species with a lone pair of electrons - can donate this pair of electrons
name the nucleophilic substitution reactions
reactions with - hydroxide - water - cyanide - ammonia
conditions for halogenoalkanes reacting with hydroxide ions and what is produced
• react with warm potassium hydroxide under reflux • to produce alcohols
in reaction with KOH what acts as a nucleophile
the OH- ion
general equation for reaction of halogenoalkane + potassium hydroxide
R-X + KOH –> ROH + KX
FLASHCARD (mechanism for reaction of bromoethane with hydroxide ions)
general equation for halogenoalkane + water
R-X + H2O –> R-OH + H+ + X-
what acts as a nucleophile in the reaction with water
water
conditions for reaction with cyanide ions
• warm, under reflux • KCN in ethanol (ethanolic solvent)
why are the CN ions in an ethanolic solvent
• if in water, substitution may occur by OH- and not CN
FLASHCARD (mechanism for reaction of bromoethane with cyanide ions)
symbol + word equation (bromoethane + cyanide ions)
CH3CH2Br + KCN –> CH3CH3CN + KBr bromoethane + potassium cyanide –> propanenitrile + potassium bromide
usefulness of reaction with cyanide ions
• used to lengthen the carbon chain • fairly easy to change the -CN into other groups
conditions for reaction with ammonia
• warm, carried out in a sealed tube • ammonia dissolved in ethanol solution (ethanolic solvent) • excess ammonia
FLASHCARD (mechanism for reaction of bromoethane + excess ammonia)
what is a base
a proton acceptor
what does the ammonia act as in the first and second reaction
first: nucleophile second: base
word and symbol equation for reaction of bromoethane with ammonia
CH3CH3Br + 2NH3 –> CH3CH2NH2 + NH4Br bromoethane + ammonia –> ethylamine + ammonium bromide
FLASHCARD (mechanism for reaction of bromoethane + water)
what type of reaction is the reaction with aqueous OH-
nucleophilic substitution
what type of reaction is the reaction with ethanolic OH-
elimination