Haloalkanes and Alkenes Flashcards
Primary halogenoalkanes
One carbon attached to the carbon atom adjoining the halogen.
Secondary halogenoalkanes
Two carbon atoms attached to the carbon atom adjoining the halogen
Tertiary halogenoalkanes
Three carbons attached to the carbon atom adjoining the halogen
What to remember when drawing the nucleophilic substitution mechanism?
Double headed arrows
Goes behind the carbon which the halogen is attached to
Make sure to draw in the dipoles
Make sure the curly arrow comes from the lone pair which is drawn in
remember about the halogen that is displaced
What nucleophiles do Halogenoalkanes undergo nucleophilic substitution?
OH-, CN- and NH₃.
What is the most unreactive and most reactive haloalkane and why?
Unreactive = Fluoroalkanes
Reactive = Iodoalkane
Iodoalkanes have more electrons and so have a larger atomic radius and so there is less attraction between the halogen and the carbon. They have a lower bond enthalpy.
Hydrolysis
The splitting of a molecule by reaction with water.
What colour is Silver Chloride?
White precipitate
What colour is Silver Bromide?
Cream Precipitate
What colour is Silver Iodide?
Yellow Precipitate
How can the rate of reaction be determined from the precipitate?
The faster the precipitate is formed, the faster the rate of reaction.
Conditions needed to substitute a halogen with an OH- ion?
Potassium hydroxide in an aqueous solution under heat.
Conditions needed for nucleophilic substitution of a CN- ion?
Ethanolic (dissolved in ethanol) Potassium Cyanide
Under heat
Conditions needed for Nucleophilic substitution of a haloalkane by NH3?
Excess Ethanolic Ammonia
Under heat and pressure
What happens in an elimination reaction?
A nucleophile attacks a hydrogen atom and such as a hydroxide nucleophile and forms an alkene and water and the halide ion.
What is ozone?
Ozone is an allotrope of oxygen which is found in the upper atmosphere and is beneficial as it filters out lots of the sun’s harmful UV radiation.
What are the three types of radiation from the sun?
UV-A (none absorbed by the ozone)
UV-B (most absorbed by the ozone)
UV-C (all absorbed by the ozone)
What is the condition needed for the decomposition of ozone?
Chlorine radicals which come from uv light breaking down the C-Cl bond
What are some examples of where CFCs were used and why were they banned?
They were used in fridges, degreasing circuit boards, as propellants in aerosols
They were banned as they were found to be damaging the ozone layer.
What are the three steps of free radical substitution and what are the conditions needed for each?
Initiation (UV light)
Propagation
Termination
Under UV light what does trichlorofluoromethane break down to?
Chlorine radicals and a dichlorofluoromethane radical
What to remember when drawing an elimination mechanism?
Remember to draw the base attacking an adjacent hydrogen and to show all the electron pairs moving.
Show water and halogen ion.
Conditions needed for electrophilic addition for Br2, Cl2 and HBr?
No conditions needed.
Conditions needed for catalytic addition with H2.
Nickel catalyst at 150°C
Conditions needed for electrophilic addition with H2O?
300°C 60ATM and H₃PO₄
Explain why Bromine, a non polar molecule, is able to react with propene?
The double bond is electron rich and forms and induced dipole with Bromine.
What features of the double bond in an alkene stop it from switching between isomers?
Restriction in rotation.
What to remember when drawing the electrophilic addition mechanism?
remember that there are three steps
make sure to draw the arrow coming from the double bond and going to the less electronegative atom
make sure to draw the carbon cation
show dipoles and temporary charges
What is the major product of any electrophilic addition?
The tertiary then secondary then primary
Why does electrophilic addition happen?
As the electrophile approaches the molecule the electron rich double bond pushes the electrons away in the electrophile molecule and it splits up.
What is a nucleophile?
A nucleophile is a reactant that provides a pair of electrons to form a new covalent bond.
What is an electrophile?
An electrophile is a species that accepts a pair of electrons to form a new covalent bond
What specifically happens when a haloalkane reacts with an ammonia nucleophile?
To start with the ammonia acts like any other nucleophile but forms an ammonia part which has a positive charge and so another ammonia molecule which now acts as a base comes along and and grabs and electron from a hydrogen to make an ammonium molecule as well.
https://www.youtube.com/watch?v=akbSB6fRlj4
Where are chlorofluoroalkanes used?
They are used in solvents.
How do chlorine radicals deplete the ozone layer and what are the propagation steps?
Cl⠈+ O₃ = O₂ + OCl⠈
OCl⠈ + O₃ = 2O₂ + Cl⠈
How can you differentiate between an E and a Z isomer?
E isomers have a greater atomic mass diagonally from each other
Z isomers have a greater atomic mass adjacent horizontal to each other
What happens in the electrophilic addition of H2SO4 with an alkene?
A hydrogen splits away from the H2SO4 and OSO2OH is left which attaches to the final open bond.
Then in step 2 water is added and the compound is hydrolysed into an alcohol and also sulfuric acid in the end.
What is the role of sulfuric acid in its electrophilic addition?
It acts as a catalyst
What is the structure of an alkene in terms of sigma and pi bonds?
The double bond contains one pi bond and one sigma bond, the pi bond is exposed and is electron rich which is what the electrophiles are attracted to.
Problems with polymers being unreactive?
They don’t decompose and if they are burnt then they release carbon dioxide which contributes to the greenhouse effect.
What are the conditions needed for elimination?
A strong base
hot ethanolic conditions
What to remember when drawing a repeating unit?
dont put down an n
You will get marked down
C-C single bond (not double)
Bonds passing through brackets
What solubility is silver fluoride?
Soluble in water so silver nitrate cannot be used to test for fluoride ion as there will be no colour change.
What to remember when talking about the quantity of products of a mechanism?
When talking about the quantity of product produced remember to mention both types of product and in what quantity and the differences in the cation intermediate.
