13.1 Halogenoalkanes properties Flashcards
What are some uses of halogenoalkanes
. They are the basis of many synthetic compounds
Eg PVC to make drainpipes,
Teflon (non stick coating on pans)
What is the structure of a halogenoalkane
What would the formula be
Alkane skeleton with one or more halogens in place of a hydrogen atom
CnH(2n+1)x where x is any halogen
How would you name a halogenoalkane
First:
Prefixes fluoro, chloro, bromo iodo
tell us which halogen is present
. Numbers are used to tell us which carbon is connected to the halogen
. Prefixes di- tri- tetra-
show how many atoms of each halogen is present
When a compound contains different halogens, they are listed in alphabetical order
On the C - x bond in a halogenoalkane, is it polar?
Yes it is polar
Because the carbon is partially positive and the halogen is partially negative
As halogens are more electronegative than carbons
Eg fluorine is the most electronegative element, so as you go down group 7 they are less electronegative so the C-x bond is less polar
Describe solubility of halogenoalkanes
what happens when they are mixed with hydrocarbons
Halogenoalkanes are NOT soluble in water
. Even though the C-X bond is polar, it is not polar enough to make them dissolve
. The main intermolecular forces of attraction in them are dipole dipole eg HF, and van der waals
Halogenoalkanes mix with hydrocarbond to be used as dry cleaning fluids to remove oily stains
Describe boiling point of halogenoalkanes
. As chain length of halogenoalkane increases, so does boiling point
. As the halogen on it goes down the group, the boiling point increases
These effects are because of van der walls, as the bigger the molecule the more electrons so stronger forces
(going down group 7 the molecules get bigger)
which have higher boiling points:
Halogenoalkanes or alkanes
Halogenoalkanes have higher boiling points than alkanes of same chain length
Because they are more polar, and have higher relative atomic masses (so more van der waals)
Do other homologous series get higher boiling points as there are more branches?
No, the more branched a chain is, the lower the boiling point
What bond in a halogenoalkane usually breaks when they react?
The C-x bond breaks usually when they react
How readily the C-x bond breaks when reacting depends on 2 factors…
- The C(f+) and X(f-) polarity
The more polar they are the less likely they are to break - The C-X bond enthalpy
The higher the bond enthalpy, the less likely the bond is to break
The bond enthalpy has a bigger impact on it than polarity
What are nucleophiles
They are electron pair doners
The halogens are more electronegative than carbons so the C is more f+ and X is f-.
This means it is electron deficient
So reagents that are electron rich or have electron rich areas (nucleophiles) can attack them
What carbon-halogen bond is most easily attacked by a nucleophile
The C-F bond is more polar as there is a bigger difference in electronegativity
So it accepts a pair of electrons from the nucleophile more easily than C-I which is the least polar
Describe the C - X bond enthalpies down the group
C-F is the strongest bond enthalpy because it is the most polar.
As F is the smallest halogen, in the bond the shared electrons are more attracted to fluorine than carbon.
So bond enthalpies decrease down the group as the halogens outer electrons get further from its nucleus so the bond is weaker
How does the C-X bond affect reactivity of halogenoalkanes
As x gets further down the group, the C-F bond enthalpy decreases so the reactivity of it increases
