This is a sample of our (approximately) 4 page long Haloalkanes notes, which we sell as part of the Chemistry AS Notes collection, a A package written at Manchester High School For Girls Sixth Form in 2013 that contains (approximately) 54 pages of notes across 17 different documents.
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Unit 2: 14 Haloalkanes
HALOALKANES Why are alkanes so unreactive?
• Both C-C bonds and C-H are non-polar therefore particles are not attracted to the alkanes
• Both C-C and C-H bonds are very strong Being so unreactive makes alkanes useful as LUBRICANTS and PLASTICS
A FREE RADICAL is a species with an unpaired electron There are 3 ways to split the shared electron pair in unsymmetrical covalent bond; HETEROLYTIC FISSION - unequal splitting of electrons so both electrons go to one atom (produces ions) HOMOLYTIC FISSION (equal splitting) occurs when a covalent bond breaks with equal splitting of the bonding pair of electrons, to produce free radicals.
SYNTHESIS OF HALOALKANES - FREE-RADICAL SUBSTITUTION MECHANISM
STEP 1: INITIATION STEP UV •
Cl2 → Cl + Cl
• UV LIGHT provides the energy needed to start the reaction by splitting chlorine molecules into free radical atoms
• This process occurs ﬁrst because the Cl-Cl bond in chlorine is weaker than the C-H bond in methane
STEP 2 & 3: PROPAGATION STEPS FIRST PROPAGATION STEP
CH4 + Cl → CH3 + HCl SECOND PROPAGATION STEP
CH3 + Cl2 → CH3Cl + Cl
Chlorine radical is regenerated - acting as a catalyst
• In each propagation step, a radical is used and a radical is form - continuous chain reaction
CH4 + Cl2 → CH3Cl + HCl TERMINATION STEPS
• CH3 + • CH3 → C2H6
• CH3 + • Cl → CH3Cl
-Such termination steps lead to trace amount of impurities in the ﬁnal products.
-You can begin the mechanism with a larger molecule to achieve a larger molecule (READ THE QU.) CHEMISTRY AS NOTES
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