Substitution Reactions

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A level Chemistry (4.1 Basic Concepts and Hydrocarbons) Flashcards on Substitution Reactions, created by Yinka F on 07/03/2018.
Yinka F
Flashcards by Yinka F, updated more than 1 year ago
Yinka F
Created by Yinka F over 6 years ago
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Question Answer
What are photochemical reactions? Reactions that are started by light
Complete the sentences: Haloalkanes are formed when _________ react with __________ in photochemical reactions. During the formation of haloalkanes, a ______________ atom is _______________ (replaced) by a halogen such as chlorine or bromine in a ___________ _____________ reaction. Haloalkanes are formed when HALOGENS react with ALKANES in photochemical reactions. During the formation of haloalkanes, a HYDROGEN atom is SUBSTITUTED (replaced) by a halogen such as chlorine or bromine in a RADICAL SUBSTITUTION reaction.
What is the name of the process involved in the synthesis of chloromethane? Radical substitution
Give the balanced symbol equation for the synthesis of chloromethane CH₄ + Cl₂ --> CH₃Cl + HCl
What are the 3 stages of radical substition? Initiation Propagation Termination
What happens during initiation? Sunlight provides enough energy to break some of the Cl-Cl bonds (this is photodissociation) The bond splits equally and gets to keep one electron (homolytic fission) These atoms are highly reactive radicals, Cl•, because each one has an unpaired electron
Give the equation for the initation stage in the synthesis of chloromethane Cl₂ --> 2Cl•
What happens during propagation? Radicals are used up and created in a chain reaction First Cl• attacks a methane molecule The new methyl radical, CH₃•, can then attack another Cl₂ The new Cl• can attack another CH₄ molecule, and so on, until all the Cl₂ or CH₄ molecules are used up
Give the equations of the propagation stage in the synthesis of chloromethane Cl• + CH₄ --> CH₃• + HCl CH₃• + Cl₂ --> CH₃Cl + Cl•
What happens during termination? If two radicals join together, they make a stable molecule - this terminates the chain reaction
Give the 3 possible equations for the termination stage in the synthesis of chloromethane CH₃• + Cl• --> CH₃Cl CH₃• + CH₃• -->C₂H₆ Cl• + Cl• --> Cl₂
What are the problems associated with radical substitution? You get a mixture of products even if you are trying to make a single particular product It can take place at any point along the carbon chain, forming a mixture of isomers
What is one solution to reducing the chance of by-products forming? Have an excess of a reactant For example, in the synthesis of chloromethane, there could be an excess of methane. There'll be a greater chance of a chlorine radical colliding only with a methane molecule and not a chloromethane molecule
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