Hello alkanes! But no time for any more jokes, THIS IS NOT A DRILL. It's time for a speed review. I haven't spedran a review before, but the time has come, as I need to cover this (thankfully not too long) topic in record time. It is currently half 1, so I need to finish this to give myself enough sleep for getting up at half 6, to get to my AS exam at quarter to 9. I have done all my other revision though, so this is just to finish off.
Nucleophiles donate a lone pair of electrons. Common nucleophiles are hydroxide, water and ammonia. Nucleophilic substitution is when the nucleophile replaces the halogen.
A great eg of this is Hydrolysis. In this reaction it involves a nuleophile like water or hydroxide, as this has an alcohol group in it, so at the end of the reaction you have an alcohol. This is also drawn with mechanisms. The electrons from the C-halogen bond goes to the halogen, and then the alcohol joins to that carbon. So haloalkane to alcohol. This is quite slow at room temp, so it can be heated under reflux to make it faster.
What about the strength in haloalkanes? A C-F bond is stronger than a C-Cl bond, and that trend follows down the group. This means for haloalkanes with the halogen lower down the group, less energy is needed to break the bond, so they are more reactive. This means fluoroalkanes are quite unreactive. Also tertiary haloalkanes react faster.
You can measure the relative rate of reaction for the haloalkanes with silver nitrate. In Chap 8 this is a test for halides, so it works the same way, with you ending up with a test tube rack of cum. In this case, ethanol is used, just cause.
Organohalogens are molecules with at least a halogen joined to a carbon chain. These have uses in things like pesticides, but they aren't too good for the environment.
An example is CFCs and the ozone layer. CFCs break apart in the atmosphere (UV light, homolytic, radicals), and the Cl reacts with the O in the ozone layer. The ozone is made of O₃, but the choline reacts to turn it to O₂. This also happens with nitrogen oxides.
Ozone is good because it absorbs harmful UV rays. Luckily CFCs are banned or something, the the ozone and us live to see another day for now.
Wow, 20 mins, quite quick.
Bye-alkanes.