3.3.3 - Haloalkanes Flashcards
How do you name haloalkanes?
Prefix: iodo-/chloro-/bromo-/fluoro-
(Can be preceded by di-/tri-/tetra-)
The halogens come in alphabetical order if there are multiple.
What is the trend with boiling points of haloalkanes
a) with different chain lengths?
b) down group 7?
c) branching?
Trend with boiling points of haloalkanes,
a) longer chain lengths: higher bpt,
b) down group 7: higher bpt,
c) decreases with branching.
How do the bpts of haloalkanes compare with those of similar chain length alkanes and why?
Higher. Due to higher Mr values and more polarity.
Main intermolecular force between haloalkane molecules?
van der Waals’ intermolecular forces.
Are haloalkanes soluble in water and why?
No: the carbon-halogen bond is not sufficiently polar.
When are haloalkanes soluble? Use?
With hydrocarbons. Uses: dry-cleaning fluids to remove oily stains.
What element is the most electronegative?
Fluorine.
Bond polarity _______ down group 7.
Decreases.
The bond becomes ____ polar down group 7.
The bond becomes LESS polar down group 7.
What is the impact of electronegative halogen atoms covalently bonded to a carbon in haloalkanes?
Withdraws electron density from the carbon, leaving it susceptible to attack from nucleophiles.
Bond enthalpy _______ down group 7. Why?
Bond enthalpy DECREASES down group 7. Because the atomic radii increase, so there is weaker attraction between the shared electrons in the covalent bond and the positive nuclei.
Reactivity of haloalkanes ______ down group 7. Why?
Reactivity of haloalkanes INCREASES down group 7. Due to decreased bond enthalpies.
Conditions and type of reaction?
a) Haloalkane -> alcohol
b) Haloalkane -> amine
c) Haloalkane -> nitrile
a) Primary alcohol Aqueous solvent Warm Nucleophilic substitution (KOH/NaOH dissolved in ethanol and water).
b) XS concentrated ethanolic ammonia and high pressure
c) aqueous ethanolic KCN
How do you add a carbon atom to the carbon chain?
Nucleophilic substitution with aqueous ethanolic KCN to make a nitrile
Define ‘nucleophile’.
Nucleophile: electron pair donor.
- A negative charged ion or has an electronegative ion.
- With a lone pair of electrons (on electronegative ion).
Name of reaction: haloalkane -> alkene?
Elimination
Conditions to form an alkene from a haloalkane?
Concentrated NaOH/KOH Hot Ethanolic solvent (ANHYDROUS) Elimination Tertiary alcohol
Do secondary alcohols usually undergo nucleophilic substitution or elimination reactions with hydroxide ions?
Both! Depends on conditions.
In elimination reactions, hydroxide ions act as ________.
Electrophiles.
Uses of chlorofluorocarbons?
Short chain: aerosol propellants and refrigerants.
Long chain: dry cleaning and degreasing solvents.
Equation of CCl3F to form a chlorine free radical?
CCl3F —UV—> CCl2F. + Cl.
3x Equations showing reactions of chlorine free radicals with ozone? What is the catalyst?
1) .Cl + O3 -> ClO. + O2
2) ClO. + O3 -> Cl. + 2O2
Overall = 2O3 -> 3O2 with .Cl catalyst.
Define ‘free radical’.
An uncharged molecule
typically highly reactive and short-lived
having an unpaired valency electron.