Haloalkanes Flashcards
Naming haloalkanes
where a halogen atom has replaced at least 1 H atom in alkane chain
naming using prefixes- fluoro chloro bromo iodo
e.g 2-chloro-3-bromohexane
classification of Haloalkanes
Classified as primary(1⁰), secondary(2⁰)or tertiary(3⁰)
based on how many alkyl groups bonded to C atom that has halogen atom
H
P - C -C-H 1 alkyl group bonded to C-X
x
H S - C C C 2 alkyl group bonded to C-X
X
C T- C C C 3 alkyl group bonded to C-X
H
Nucleophile
An electron pair donor (must possess a lone pair of electrons) e.g. :OH- :NH3 H20: :CN- (Cyanide ion)
attracted to electeon deficient C bond
Haloalkanes functional group
functional group- C- halogen bond
this bond is polar as halogen atom is more electronegative than carbon
forms electeon deficient C atom(C dipole +)
Hydrolysis- haloalkanes
nucleophillic substitution reaction
electron pair donor replaces halogen atom
involves water or aqueous solution of OH- ion that causes breaking of bond in molecule
split into 2 products
reagents: aqueous alkali e.g. NaOH
conditions: heat under reflux (cont boiling and condensing of liquid allowing prolonged heating preventing loss by evap)
example equation:
full- CH3CH2CH2CH2Cl + NaOH –> CH3CH2CH2CH2OH + NaCl
ionic- CH3CH2CH2CH2Cl + OH- –> CH3CH2CH2CH2OH + Cl-
Nucleophillic substitution mechanism
e.g. CH3CH2CH2CH2Cl + OH-
l - l
H l v H
CH3CH2H2 C–l–Cl > CH3CH2H2C C OH
———l> H H
l
l—:OH- :Cl-
add positive dipole to C and negative to Cl in first
Nucleophile is attracted to the electron deficient C atom
donates lone pair of electrons to form covalent bond
c cl breaks by hetrolytic fission both electron move to Cl
2 products produced
reactivity of haloalkanes
depends on strength of C halogen bond
if strong then more energy to break so less reactive
if weak less energy to break so more reactive
increases reactivity + decreasing bond enthalpy ——>
fluoroalkanes, chloroalkanes, bromoalkanes, iodoalkanes
measing rate of hydrolysis of primary haloalkanes
reagent: aqueous silver nitrate AgNO3
conditions: Ethanol solvent and heat (water bath)
in this nucleophile is water
hydrolysis:
CH3CH2CH2CH2Cl + H2O —>CH3CH2CH2CH2OH + HCl (H+,Cl-)
then:
Ag+ + Cl- —–> AgCl, silver chloride(white)
Method:
place set amount of haloalkane in test tube in water bath at 50 degrees c
place set amount of ethanol + AgNO3 into another test tube in same water bath at same temp
when both same temp add contents of one to another and replace in water bath
time how long for precip to form
rate of hydrolysis = 1/time
e,g, fluoroalkane should be slow and have slowest rate as least reactive
strongest bond strength requires more energy to break bonds
What are CFCs
Chlorofluorocarbons type of haloalkane
with multiple halogen atoms
inert, non toxic, non flammable
used in refrigirators, aerosol propellents amd solvets
no longer used as they result in delptetion of the almosphere
now we use HCFs Hydrogenfluorocarbons and HCFCs Hydrocholorofluorocarbons
what is? How formed? what has happend to? and what is the effect of deleption of?, The ozone layer
what is? region of stratosphere the absorbs most of suns harmful UV
contains high conc of Ozone
Formation? continually forms ozone and continually broken down by UV
02 > 2O.
then equ set up with O2 and radicals
O2 + O >< O3
rate of formation=rate of depletion
Happend? use of CFCs increased rate of depletion casuing hole in ozone layer
effect? less protection from suns UV radiation e.g. rise in skin cancer
How have CFCs cause ozone breakdown
produce Cl. in stratosphere by homolytic fission of C Cl bond, acts as a catalyst and catalyses ozone breakdown
initiation: CFCl3 > Cl. + CFCl2
prop: Cl. + O3 > ClO. + O2
ClO. + O > Cl. + O2
overall: O3 + O > 2O2
other radicals that also effect ozone
NO. produced in atmosphere during lighting strike/ inside jet engine
N2 + O2 > NO.
NO. + O3 > NO2. + O2
NO2. + O > NO. + O2
O3 + O > 2O2
