Lecture Notes Week 11

Lecture Notes Week 11 - ORGANIC REACTIONS (refer to bottom...

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1 ORGANIC REACTIONS (refer to bottom of page 46 in organic notes) CHEMICAL PROPERTIES OF ALKANES generally lacking in reactivity due to strength & non-polar nature of bonds inert to common strong acids (H 2 SO 4 , HCl) inert to common strong bases (NaOH) inert to oxidising agents (MnO 4 2 O 7 2– ) inert to reducing agents (Na) Much of the chemistry of alkanes involves free radicals. Types of Alkane Reactions 1. Pyrolysis (or cracking) – decomposition of compound by heating usually in presence of a catalyst. 2. Combustion – burn in the presence of O 2 3. Halogenation – react with a halogen in the presence of U.V. light or heat. a. Chlorination : (see also page 1007 in text) an example of a very large class of organic rxns known as substitution reactions reaction with Cl 2 , UV light or heat CH 4 CH 3 Cl + HCl very difficult to control CH 3 Cl CH 2 Cl 2 + HCl CH 2 Cl 2 CHCl 3 + HCl CHCl 3 CCl 4 + HCl products separated by fractional distillation b. Bromination : rxn with Br 2 , UV light or heat CH 4 + Br 2 CH 3 Br + CH 2 Br 2 + CHBr 3 + CBr 4 Reactivity of halogens: F 2 > Cl 2 > Br 2 > I 2 Preferred order of reactivity with H’s in molecule: tertiary (3 ° ) > secondary (2 ° ) > primary (1 ° ) have MAJOR and MINOR products CHLORINATION REACTION MECHANISM: 1) Cl 2 2Cl chain initiation step H H 2) Cl + H-C-H H-C +HCl H H chain propagation steps CH 3 + Cl 2 CH 3 Cl + Cl 3) 2 Cl Cl 2 2 CH 3 CH 3 CH 3 chain termination steps CH 3 + Cl CH 3 Cl
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2 (pg 48) A. Electrophilic Additions : (see also page 1010 in text) ¾ π bond source of electrons ¾ attracts electrophilic agent ¾ two step process: >C=C< + A + –C–C– + B –C–C– A + A B where A + B represents HCl, HBr, HI or H + /H 2 O Preferred position of B : 3 ° C > 2 ° C > 1 ° C (“Markovnikov’s Rule”) B. Catalytic Hydrogenation (or reduction): ¾ H 2 adds to π bond with a catalyst ¾ addition to same side of C=C bond
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This note was uploaded on 04/17/2011 for the course CHEM 1040 taught by Professor Prokiacpak during the Spring '08 term at University of Guelph.

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Lecture Notes Week 11 - ORGANIC REACTIONS (refer to bottom...

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