5. Haloalkanes Flashcards
(26 cards)
What is the functional group of a haloalkane?
C-X.
How are haloalkanes named?
As substituted alkanes with the position of the halogen atom(s) indicated by locant numbers where necessary.
How are haloalkanes classed?
Primary (if the bonded carbon is also attached to two hydrogens)
Secondary (if the bonded carbon is attached to one hydrogen)
Tertiary (if the bonded carbon is not attached to any hydrogens)
What are the physical properties of haloalkanes?
Strong polarity of C-F and C-Cl bonds create permanent dipole attractions between fluoroalkanes and chloroalkanes.
Van der Waals forces are also present.
If the molecule is symmetrical, dipoles will cancel and it will not be polar.
What are the trends in boiling point of haloalkanes?
Higher than expected with other molecules of similar RFM with F and Cl due to permanent dipole attractions caused by electron distribution.
General increase descending the group as well due to more electrons and more van der Waals.
Why do secondary haloalkanes have slightly lower boiling points than primary ones?
The molecules cannot make as much contact with one another because the large halogen atom is in the middle
Other physical properties of haloalkanes?
Sickly-sweet smell
Liquid haloalkanes are immiscible with water and form two layers
Trends reactivity of hydrogen halides and classes of haloalkanes?
Increase downwards
Increase from primary to tertiary
Preparation of a haloalkane from an alcohol?
Butan-1-ol + hydrogen bromide -> 1-bromobutane
Hydrogen bromide generated in situ from the reaction of sodium bromide with concentrated sulfuric acid
THERE’S A WHOLE BIG REACTION THAT I’M SKIPPING KAY
KAY
Define “reflux”.
Continuous boiling and condensing of the reaction mixture.
How to produce a haloalkane from an alkane?
Add alkane and halogen, using photochemical free-radical substitution, and get haloalkane and hydrogen halide
How to produce haloalkane using alkene?
Alkene and hydrogen halide makes haloalkane.
Electrophilic addition reaction with no specific requirements
How to produce haloalkane using alcohol?
Alcohol and hydrogen halide gives haloalkane and water.
Substitution reaction. Standard method.
Had generated in situ from NaX and concentrated sulfuric acid
Heat under reflux
Haloalkane + alkali (OH-)?
Gives alcohol and halide ion.
Heat under reflux with aqueous sodium hydroxide solution and small quantity of ethanol for an hour
Nucleophilic substitution reaction
Or hydrolysis
Haloalkane + alkali (OH-) but specifically hydrolysis?
Bonds in the reactant molecule broken by water molecules. One part binds with H, one with O.
Can be catalysed by acid or alkali.
Trends in haloalkane bond length, enthalpy, and polarity?
Bond length increases downwards
Bond enthalpy decreases downwards
Bond polarity decreases downwards
Testing ease of hydrolysis experimentally?
Add 1cm3️⃣ of 1-chlorobutane, 1-bromobutane, and 1-iodobutane in three flasks, and add 2cm3️⃣ ethanol. Add 1cm3️⃣ silver nitrate solution.
Length of time for ppt to form.
Haloalkane reaction with ammonia, NH3?
Haloalkane + ammonia -> amine + HX
Requires heating with ethanoic ammonia in a sealed tube
Nucleophilic substitution
Amine (NH2) subs with X
Haloalkane reacting with cyanide ions, CN-?
Haloalkane + CN- -> Nitrile + Halide
Haloalkane dissolved in ethanol dropped into aqueous solution of KCN or NaCN. Mixture heated under reflux.
Nucleophilic substitution
Haloalkane reacting with potassium hydroxide, KOH, in ethanol?
Haloalkane + KOH -> Alkene + KX + water
Haloalkane treated with hot ethanoic potassium hydroxide solution
Elimination reaction
Define “elimination reaction”.
When a small molecule such as HX is removed from a larger molecule and not replaced with anything else
Stages of mechanisms?
Initial reactants, including polarity of any relevant bond
Intermediate or transition state
Products of the reaction
Define “nucleophile”.
An electron-rich species (negative ion or molecule with a lone pair of electrons) that can attack an area of low electron density such as a positive ion or the delta+ end of a polar bond.
