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Chemistry: Mechanism Flashcards
Terms in this set (11)
Free radical substitution
Requires UV light for halogen radicals to form. They then act as a catalyst in the production of the eventual product. A termination step occurs when two radicals meet to form a stable molecule.
An excess of methane should be used if only chloromethane is to be produced (otherwise further substitution may occur)
An excess of chlorine should be used if tetrachloromethane needs to be produced.
The reaction always produces a mixture, and apart from the relative ratios of the products it is uncontrollable
Nucleophilic substitution (OH-)
Forms an alcohol.
Nucleophilic substitution (CN-)
Note that this extends the length of the carbon chain. Forms a nitrile.
Nucleophilic substitution (NH3)
Note that two ammonia molecules are needed for the full substitution, though one forms ammonium. Forms an amine.
The nucleophile must have a lone pair that can be used for bonding and a partial or full negative charge. Heat under reflux with a dilute aqueous ethanolic solution. Primary > Secondary > Tertiary in terms of reaction rate. Also depends on the strength of the C-X bond, where X is the halogen. For ammonia, heat in a sealed tube, and use excess ammonia to avoid creating secondary or tertiary amines.
Elimination of haloalkanes
Heat under reflux with a hot concentrated ethanolic solution of sodium hydroxide. Tertiary > Secondary > Primary in terms of reaction rate. The hydroxide ion acts as a base. Produces an alkene as the product.
Alkenes: electrophilic addition of HBr
Forms a haloalkane as the product.
Alkenes: electrophilic addition of Br2
This will turn bromine water colourless, and so can be used as a test for alkenes
Alkenes: electrophilic addition with sulfuric acid
This is one step in the hydration of ethene with a sulfuric acid catalyst to form ethanol
Hydration of ethene with acid catalyst
Only the H+ ion is shown here. The acid catalyst is needed as the H+ ion is a better electrophile than H2O. Forms ethanol.
Dehydration/elimination of ethanol
Here, the H+ ion is needed to make a better leaving group (H2O is preferred over OH-). It acts as a catalyst. Forms ethene.
Recommended textbook explanations
Chemistry Matter and Change
Buthelezi, Dingrando, Hainen, Wistrom
Matta, Staley, Waterman, Wilbraham
Holt McDougal Modern Chemistry
Sarquis, J., Sarquis, M.
Myers, Oldham, Tocci
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