Haloalkanes Flashcards
(18 cards)
what is the general formula of a haloalkane
CnH2n+x
x = halogen
what are the three types of haloalkane
primary
secondary
tertiary
what is the solubility of haloalkanes
not generally soluble in water
there is no hydrogen bonding between them
what type of bond do haloalkanes contain and why is it important
C-X bond where X = F, Cl, Br or I
it has a permanent dipole
C is delta +, X is delta -
what is a nucleophile and which are the most common
electron pair donor
OH- , CN- , NH3
what reaction do haloalkanes undergo
nucleophilic substitution reactions
what is a nucleophilic substitution reaction with hydroxide ions
reagents - aq sodium hydroxide in ethanol
conditions - RTP
equation - CH3CH2Cl + NaOH —> CH3CH2OH + NaCl
what do you need to remember for the mechanism of nucleophilic substitution
lone pairs
dipoles
charges (in circles)
curly arrows - from lone pairs to C or from bond to X
what is a nucleophilic substitution reaction with cyanide ions
reagents - aq potassium cyanide in ethanol
conditions - RTP
equation - CH3CH2Cl + KCN —> CH3CH2CN + KCl
K is not included in the mechanism as it is a spectator ion
what is a nucleophilic substitution reaction with ammonia
reagents - ethanolic acid in excess
conditions - RTP in a sealed vessel
equation - RCl + 2NH3 —> RNH2
what 2 things differ about the C-X bond in different haloalkanes
dipoles
bond enthalpy
bond enthalpy more important
how does polarity change down the haloalkane group
difference in electronegativity gets smaller
dipole decreases
nucleophiles attracted less
rate of reaction decreases
how does bond enthalpy change down the haloalkane group
shared pair of electrons further away from nucleii
attraction decreases
bond weaker
bond enthalpy decreases
rate of reaction increases
what is the hydrolysis experiment
add 2cm3 ethanol to 3 test tubes
add 1cm3 silver nitrate to each test tube
warm in hot water for 2 mins
add 3 drops of a different haloalkane to each tube, add stopper + shake
note how fast a precipitate forms
I reacts fastest, Cl reacts slowest
what are CFCs
all H atoms on a hydrocarbon are replaced by Cl or F
C-F and C-Cl bonds are strong so they are very unreactive
tetrahedral - bond angle = 109.5°
what are CFCs useful for
refrigerants
aerosol propellants
in packaging material
what effect do CFCs have on the ozone layer
they form Cl radicals when they enter the ozone layer which damage it
the presence of UV light breaks the C-Cl bond
CCl2F2 —uv—> °CClF2 + Cl°
once the Cl free radical is formed it broke down the ozone as it was used in the first step
O3 + Cl° —> O2 + ClO°
and recreated in the second
ClO° + O —> O2 + Cl°
Cl radicals are catalysts in this reaction
what happened to the use of CFCs after research
they were banned
replacements were developed that didn’t contain Cl (HFCs)
C-F bond stronger than C-Cl bond so should not be broken by UV light
