Chapter 15 Flashcards
What are haloalkanes ?
Hydrocarbon chain with halogen attached (F, Cl, Br or I)
The halogen atom forms a covalent bond with a carbon atom
The halogen causes the relatively unreactive carbon chain to become more reactive.
They are saturated organic compounds that contain Carbon atoms and at at least one halogen atoms
Are haloalkanes soluble in water ?
Insoluble as C-H bonds are non polar, not compensated enough by C-X bond
Do haloalkanes have a polar bond and why ?
Yes because the halogen has a higher electronegativity than C ( halogen is delta -, C is delta + )
What type of intermoelcular forces are present in haloalkanes and why ?
Permanent dipole permanent dipole interactions and london forces
C-X bond polarity creates permanent dipoles
When does the boiling point of haloalkanes increase ?
Increasing Carbon Chain length
Halogen further down Group 7
How would the mass of a haloalkane compare with the mass of an alkane of the same length ?
Greater because mass of halogen > mass of H
Properties of haloalkanes
Melting and boiling points are slightly higher than alkanes
The more halogens present (or bigger the halogen present) the greater the increase in boiling point
Haloalkanes are immiscible with water
Haloalkanes make good solvents for organic compounds
What is the most important factor in determining halogen reactivity ?
The strength of the carbon halogen bond
What would bond polarity suggest the order of reactivity be ?
C-F would be most reactive as most polar bond - the most energy is required to break this bond.
What would bond enthalpies suggest the order of reactivity would be ?
C-I would be most reactive as lowest bond enthalpy - The least energy is required to break this bond.
Rank the C-Halogen bonds in terms of polarity and strength - from highest to lowest
C-F > C-Cl > C-Br > C-I
Primary halogen vs Secondary halogen vs Tertiary halogen
Primary : 2 hydrogens attached to C containing halogen atom
Secondary : 1 hydrogen attached to C containing halogen atom
Tertiary : 0 hydrogens attached to C containing halogen atom
Define nucleophile
Electron pair donor
1) have a lone pair or negative charge
2) are attracted to a carbon with a Ξ΄+
3) form a (dative) covalent bond.
Give 3 examples of nucleophiles
:OH-
:CN-
:NH3
What is nucleophillic subsitiution ?
A reaction where a lone pair of electrons to πΏ+ C atom, πΏβ atom leaves molecules ( replaced by nucleophiles )
What is hydrolysis ?
A reaction where water or aqueous hydroxide ions are reactants and used to break / hydrolyse a bond
What is produced when haloalkanes are hydrolysed ?
An alcohol is produced as well as halide ions
What reactant produces hydroxide ions for hydrolysis ?
Water
What fission does water undergo to produce OH- ?
Heterolytic fission
Draw the mechanism for the reaction of bromoethane with NaOH
β¦
What are CFCs ?
Chlorine-fluoro-carbons - haloalkanes containing C, F and Cl only
( no H )
4 properties of CFCs
non-toxic, volatile, non-flammable, low reactivity.
What is the problem with CFCs ?
Although unreactive under normal conditions, they catalyse the breakdown of ozone in the atmosphere via free radical substitution
What is the main function of the ozone layer ?
Provides protection from harmful UV radiation
Does ozone play a protectional role in all layers of the atmosphere ?
No, in the troposphere it contributes towards photochemical smog
How do CFCs break the ozone layer down ?
Free radical substitution
Write an equation for the overall decomposition of ozone into oxygen
2O3 β 3O2
How and why are halogen radicals produced ?
The production of halogen radicals occurs by the action of ultraviolet (UV) radiation on CFCs in the upper atmosphere and results in the catalysed breakdown of the Earthβs protective ozone layer
Write free radical substitution equations to show how Cl free radicals catalyse the decomposition of O3
Propagation step 1 Cl . + O3 β ClO . + O2
Propagation step 2 ClO . + O β Cl . + O2
Overall equation O3 + O β 2O2
Write free radical substitution equation to show how nitrogen monoxide can decompose ozone
Propagation step 1 NO . + O3 β NO2 . + O2
Propagation step 2 NO2 . + O β NO . + O2
Overall equation O3 + O β 2O2
Write the general free radical substitution equation to show how βXβ can decompose ozone
Propagation step 1 X . + O3 β XO . + O2
Propagation step 2 XO + O β X . + O2
Overall equation O3 + O β 2O2
