lecture 16 - Organic Lecture Series CH 310/318 M LECTURE 16...

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Organic Lecture Series 1 CH 310/318 M LECTURE 16 Textbook Assignment: Chap 8-Cont’d Today’s Topics: Free Radical Substitution Free Radical Substitution Notice & Announcements: (No HW this week) Organic Lecture Series 2 Haloalkanes Haloalkanes Chapter 8 Chapter 8
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Organic Lecture Series 3 C-F bonds are stronger than C-H bonds; C-Cl, C-Br and C-I bonds are weaker. C-H C-F C-Cl C-Br C-I Bond Bond Leng th (pm) Bond Dissociation Ethalpy [kJ (kcal)/mol] 109 142 178 193 214 414 (99) 464 (111) 355 (85) 309 (78) 228 (57) Bond Length & Strengths Bond Length & Strengths Organic Lecture Series 4 • If a mixture of methane and chlorine is kept in the dark at room temperature, no change occurs. • If the mixture is heated or exposed to visible or ultraviolet light, reaction begins at once with the evolution of heat. • Substitution: Substitution: A reaction in which an atom or group of atoms is replaced by another atom or group of atoms. CH 4 Cl 2 3 HCl + heat + Methane Chloromethane (Methyl chloride) Δ H 0 -100 kJ (23.9 kcal)/mol Halogenation of Alkanes Halogenation of Alkanes
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Organic Lecture Series 5 – If chloromethane is allowed to react with more chlorine, a mixture of chloromethanes is formed. CH 3 Cl 2 2 2 HCl + heat + Chloromethane (Methyl chloride) Dichloromethane (Methylene chloride) 2 2 2 CHCl 3 2 CCl 4 Trichloromethane (Chloroform) Tetrachloromethane (Carbon tetrachloride) Halogenation of Alkanes Halogenation of Alkanes Organic Lecture Series 6 • Bond Dissociation Enthalpies (BDE) 2 =CH- H 2 =CH 3 - H 3 3 2 - H 3 2 (CH 3 ) 2 CH- H 3 ) 2 3 ) 3 C- H 3 ) 3 C C 6 H 5 2 - H C 6 H 5 2 2 =CHCH 2 - H 2 =CHCH 2 Benzyl Allyl Vinyl Methyl Ethyl Isopropyl tert- Butyl 372 (89) 376 (90) 405 (97) 414 (99) 421 (101) 439 (105) 464 (111) Hydrocarbon Radical Name of Radical Δ H 0 kJ (kcal)/mol Vinylic Benzylic Allylic Type of Energetics Energetics Increasing E Increasing Stability
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Organic Lecture Series 7 Radical: Radical: any chemical species that contains one or more unpaired electrons.
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This note was uploaded on 10/20/2011 for the course CH 310 M taught by Professor Iverson during the Fall '09 term at University of Texas at Austin.

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lecture 16 - Organic Lecture Series CH 310/318 M LECTURE 16...

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