O2 CHAIN INITIATION Name for this step: Cl2 + h  2Cl* Drill and Practice with Free Radical Substitution Mechanism for Chlorination of Methane Name for this step: Cl2 + h  2Cl* CHAIN INITIATION What common molecule can stop or slow the free radical substitution reaction ? O2

What is the second step of the methane chlorination mechanism ? Drill and Practice with Free Radical Substitution Mechanism for Chlorination of Methane (continued) What is the second step of the methane chlorination mechanism ? Step 2) Cl* + CH4  HCl + CH3* (radical) What is the name of the step(s) that rationalize the high photoyield of the methane chlorination reaction ? CHAIN PROPAGATION

CH3* + Cl2  CH3Cl + Cl* TERMINATES THE CHAIN REACTION Drill and Practice with Free Radical Substitution Mechanism for Chlorination of Methane (continued) Radical-radical recombination reactions have what effect on the radical chlorination reaction of methane ? TERMINATES THE CHAIN REACTION What step follows: Step 2) Cl* + CH4  CH3* + HCl STEP 3) CH3* + Cl2  CH3Cl + Cl*

Which of the 5 facts is missing ?? Drill and Practice with Free Radical Substitution Mechanism for Chlorination of Methane (continued) Which of the 5 facts is missing ?? reaction will only go at >250oC in dark or with input of ultraviolet (uv) light. in xs Cl2 , a single photon (h) event causes thousands of halogenations. O2 causes halogenation reaction to slow or stop. Reactivity rate follows: F2 > Cl2 > Br2 >I2 Wavelength of uv light that initiates reaction is the decomposition wavelength for the halogen

Which is not a step in the radical chlorination mechanism of methane?: Drill and Practice with Free Radical Substitution Mechanism for Chlorination of Methane (continued) Which is not a step in the radical chlorination mechanism of methane?: Cl* +CH4  CH3* + HCl Cl* +Cl*  Cl2 CH3 + HCl  CH3Cl + H* Cl2 + CH3* CH3Cl + Cl* c) CH3 + HCl  CH3Cl + H*

Chain termination, chain initiation and chain _______________ Drill and Practice with Free Radical Substitution Mechanism for Chlorination of Methane (continued) Chain termination, chain initiation and chain _______________ propagation What reaction explains the quenching effect of O2 on the radical substitution of Cl on methane ?? CH3* + O2 CH3OO * methylperoxy radical (~ stable)

Activation barrier/energy Drill and Practice with Free Radical Substitution Mechanism for Chlorination of Methane (continued) Activation barrier/energy energy Step 2: CH4 + Cl* What’s this barrier/energy called ? What reaction step and reaction here ? Time or reaction progress

HX + CH3* What does the Xmas seal `activated complex’ sign stand for ? Drill and Practice with Free Radical Substitution Mechanism for Chlorination of Methane (continued) What does the Xmas seal sign stand for ? `activated complex’ energy HX + CH3* What species lives here? Time or reaction progress

Step 3: Cl2 +CH3 CH3Cl + Cl* What reaction step and reaction here ? Drill and Practice with Free Radical Substitution Mechanism for Chlorination of Methane (continued) What reaction step and reaction here ? energy Step 3: Cl2 +CH3 CH3Cl + Cl* Name of postulate connected to activated complex picture Hammond Postulate Time or reaction progress

ANY DAY DOING ORGANIC CHEMISTRY IS A ____________DAY GOOD