3.3.3 Halogenoalkanes

What is the trend in bond polarity of halogenoalkanes

Larger halogens causes a decrease in bond electronegativity

What IMF do halogenoalkanes have

Van Der Walls and dipole-dipole

Why don’t halogenoalkanes have no hydrogen bonds

No direct hydrogen and halogen bonds

What is the trend with boiling points in halogenoalkanes

Lower electronegativity increases boiling point

Why does boiling points increase despite decrease in polarity

Size of an atom has a greater effect on Van der walls

Define immiscible

Does not mix well with water

Why do halogenoalkanes not mix with water

They are generally non-polar

Why are halogenoalkanes reactive

Due to their polar C-halogen bond

What functional groups are halogenoalkanes

Alcohols, amines, nitriles and alkenes

How are alcohols, amines and nitriles reacted

via nucleophilic substitution

How are alkenes reacted

Via eliminations

Define nucleophilic

Positive-loving (attracted to positive) so most likely negative

Define a nucleophile

An electron pair donor

What does a curly arrow represent

Movement of an electron pair

What does the nucleophile do in nucleophilic substitution

Attacks the delta positive carbon

What does the electron pair from the nucleophile form

A new bond to C

What are the reagents for a alcohol nucleophilic substitution

KOH (aqueous)

What is a reagent

Added to react

What conditions are needed for nucleophilic substitution

Heat and reflux

What is a conditions

Helps a reaction

Where do the curly arrows go from

The bond

Where must the arrow go from on the nucleophile

The lone pairs

Define substitution reactions

Can involve nucleophile that are not charged but have a lone pair of electrons

Name 3 examples of nucleophiles for nucleophilic substitution

OH, C triple bond N, NH3,

why is excess NH3 used in nucleophilic substitution

To prevent secondary or tertiary amines

What mechanisms turns halogenoalkanes to alkenes

Elimination

How does eliminations of halogenoalkanes make alkenes

By losing the halogen atom and forming a C=C bond in the molecule without adding anything

What is used instead of a nucleophile in elimination

A base

Where does the first arrow go in elimination

From the base to the hydrogen of the H-C bond

What hydrogens can be used in elimination

Those bonded to carbons ADJACENT to the halogen

Why can the hydrogen in elimination not be connected to the halogen’s carbon

So the carbon doesn’t lose too many electrons when the halogen is displaced

Where does the second arrow in elimination go

From the carbon-halogen bond to the halogen

Why does the second arrow in elimination go from the C-halogen bond to the halogen

As carbon gives its electrons to the halogen so it can remove itself

Where does the third arrow go in elimination

From the hydrogen to the carbon connected to the halogen

Why does the third arrow go from the hydrogen to the carbon In elimination

Hydrogen gives its electrons to the C-C bond to make it C=C

What must the reagents be for elimination

Ethanoic KOH

What are the conditions for elimination

Warmth

what is the weakest carbon-halogen bond

C-I

what is the strongest carbon-halogen bond

C-F

What can halogenoalkanes react with to form a precipitate

aqueous silver nitrate solution

what will aqueous silver nitrate form with chlorides

white precipitate

what will aqueous silver nitrate form with bromides

cream precipitate

what will aqueous silver nitrate form with iodides

pale yellow precipitate

what are halogenoalkanes so reactive

due to the electronegative halogens

what two mechanisms can halogenoalkanes undergo

elimination, nucleophilic substitution

what is the issue with chlorofluorocarbons

their effect on the ozone layer

what happens to chlorofluorocarbons in the upper atmosphere

UV radiation is absorbed forming chlorine radicals which break down the ozone layer

what is used in replacement of chlorofluorocarbons

hydrofluorocarbons

why is the ozone layer important

it absorbs harmful UV which can cause skin cancer