15 - Haloalkanes

Nucleophilic substitution

Heat under reflux and using in situ products

As you go down group, bond strength decreases Less energy is required to break C-I bond than C-Cl

Using AgNO3 to see how fast it precipitates

Ethanol - allows water and haloalkane to mix and produce a single solution rather than two layers

Molecules that contain at least one halogen atom joined to a carbon chain

• pesticides • aren’t broken down naturally which causes concern…

outer edge of stratosphere = 10 to 40 km above earths surface

ozone absorbs UV-B which is highly damaging and so prevents too much to not come on earths surface UV-B = linked to sunburn, genetic mutations and risk of skin cancer

• continually formed and broken due to action with UV rays: 1. O2 ———> 2O = broken due to energy making radicals Overall: O2 + O ———>< O3 = formed with oxygen at the same rate Overall: O

Human activity such as production of CFC’s

• AC units • aerosols • refrigerants

Due to their strength/ stability with C-X bond

• they remain stable until they reach stratosphere = due to their large residence time and takes them years to reach stratosphere • here they break down forming chlorine radicals which catalyse the breakdown of ozone; UV breaks them and as C-Cl is weakest out of all this breaks first

• Cl* + O3 ———> ClO* + O2 • ClO* + O ———> Cl* + O2 Overall: O3 + O ———> 2O2

A single CFC molecule can promote the breakdown of 100,000 mols of ozone

NO* formed from lightening strikes and aircraft travel in stratosphere • NO* + O3 ———> NO2* + O2 • NO2* + O ———-> NO* + O2 Overall: O3 + O ———> 2O2