Organic Chemistry Notes For AS/A2 OCR

In this blog I will attempt to go over the organic content for OCR AS and A2 Chemistry. This is primarily for my own benefit, but feel free to use this material as it is free and open source (like Mozilla Firefox).


Words in bold such as hydrocarbon will be defined in a glossary I will be making!


If you want to find a term quickly use the Find feature on your internet browser (usually Ctrl-F or Command-F on a Mac)


Also, please comment so I can fix any mistakes and also to show your appreciation or disappointment so I can make improvements in the future.


1. The basics


Organic chemistry is the study of compounds that contain both hydrogen and carbon. These compounds are therefore called hydrocarbons (a portmanteau of the 2 elements these compounds is made of).


Carbon is present everywhere, even as I type (and you read) we are breathing out carbon dioxide (CO₂)
which is then absorbed by plants and converted back into oxygen via photosynthesis.  Carbon is also present in the alcohol we drink, the sugar we eat, in pharmaceutical drugs we take and even the plastics we use. All of which are organic compounds!


2. Naming of hydrocarbons (prefixs)


Some of the naming of hydrocarbons is covered in GCSE, but I'll cover all the naming anyway.


The name of a hydrocarbon is varied upon several factors:


1. How many carbons it has.
2. What functional group it has and where it is in the compound.
3. Whether the compound has methyl groups and where they are if it does.


With that said, here is a list of some of the prefixs of organic chemistry (based on the number of carbons):


1. Meth
2. Eth
3. Prop
4. But (pronounced as Buut)
5. Pent
6. Hex
7. Hept
8. Oct
9. Non
10. Dec


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(I doubt anyone will need these, but I'll add them anyway.)


11. Undec (like uno is 1 in Spanish and a decahedran is a 10 sided shape)
12. Dodec
13. Tridec
14. Tetradec
15. Pentadec


20. Eicos (even I can't think of an easy way to remember this one!)


30. Tricont (just think of tri as three)


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Apart from realising that October should be the 8th month in a year and December should be the 10th. There is a pattern starting from Pent which can help you remember the prefixes, so just think of a pentagon which has 5 sides and you'll know how to name a hydrocarbon with 5 carbons.


Eg:

Pentane

This is an example of an alkane called Pentane. Of course, that is the first hydrocarbon compound I'm going to start off with...


3. Alkanes


Alkanes are without a doubt the most basic form of hydrocarbon, they have no functional group and therefore only consist of single bonded hydrogens and carbons.


When naming an alkane, use the prefixs above (Meth, Eth, Prop...) and as a suffix to end use Ane.


So for Pentane it has 5 carbons so it has the Pent prefix and it is alkane because of its single bonds its correct suffix is Ane, so; Pent + Ane = Pentane.


It's also important to remember the general formula of an alkane as C_nH_2n+2 

Replacing n as the number of Carbons and Hydrogens in the compound.

Meaning that to figure Pentane, we first look at the number of carbons it has (which is 5) so we know it is C₅, then we multiply the carbon number by 2 (so 5x2=10) then add 2 (10+2=12) meaning the formula for Pentane is C₅H₁₂ (And if you don't believe me try counting the hydrogens in the diagram).

Try working out the general formulas of: Propane, Hexane and Nonane!

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Now to look properly at alkanes and what they do!

Alkanes are known for their difficulty in reacting with other chemical compounds thanks to their strong single bonds. Apart from combustion, alkanes don't anything else on their own and therefore must be reacted with a halogen (Such as Chlorine or Bromine) under U.V. light to produce its respective halogenalkane along with an acid.

So let's look at Pentane again and react it with chlorine:

C₅H₁₂ + Cl2 → C₅H₁₂ + Cl• + Cl•

C₅H₁₂ + Cl• + Cl• → C₅H₁₁Cl + HCl    

        

This type of reaction is called radical substitution and I have done a diagram to show what's happening here:

Pentane

Chlorine goes to Pentane

UV splits the chlorine homolytically (homolytic fission) into 2 chlorine free radicals.

 

Chroline radicals have been created and now one of them has reacted with this carbon and the hydrogen underneath it has been pushed off.

Now the halogenalkane 1,Chloropentane has formed, the Chlorine radical reacts with hydrogen to produce Hydrochloric Acid.

Both the halogenalkane and acid have been formed, so the reaction is complete.
 

4. Halogenalkanes

 

Once a halogenalkane has been formed it's possible to create many different hydrocarbon compounds and therefore this reaction increases the alkane's usefulness!

When named they are refered as their halogen (like chroline) and then there respective alkane (like ethane) so Chloroethane is a halogenalkane with 2 Carbons 5 Hydrogens and 1 Chroline meaning their general foruma is Cn H2n-1 X (X being the halogen).

This is due to the alkane now being polar thanks to the halogen, this means that 2 or more elements in the compound are charged and can be attacked by electrophiles or nucleophiles

Here are 3 reactions to demonstrate what halogenalkanes can do by taking part in many different reactions:

Halogenalkane + NaOH → Alcohol

Halogenalkane + NH₃ → Amine

Halogenalkane + H₂ ( Sn + H₂SO₄) → Alkene

Halogenalkanes are useful, XD!

5. Alkenes

Alkenes are like alkanes but have a double bond connected to one of the carbons. This double bond is created from the covalent sharing of 2 electrons between carbons rather than just 1 in alkanes. The double bond is very negative so this means that alkenes are very reactive and therefore are extremely useful.

Alkenes have a general formula of Cn H2n and the lowest alkene is ethene (no such thing as methene) .


A test to show a compound is an alkene is the bromine water test shown below.


So let's look at Pentene again and react it with bromine water (known as the bromine water test):

C5H10 + Br2 → C5H9Br + HBr

Pentene is colourless (or transparent, see-through) but when bromine water is added the solution goes a reddish brown colour (because bromine water is a reddish brown colour) and then colourless as the halogenalkane 1, Bromopentane is formed along with hydrogen bromide.

It's worth noting this test will work with any halogen (though florine and asatine aren't used because they are impractical).


6. Alkynes:

Alkynes are very similar to alkenes, except they have triple bond meaning that the carbons covalently bond with 3 electrons making a much more negative centre than alkenes meaning they're more reactive. Alkynes aren't covered in the text book but they can appear in the examination itself! There suffix is "yne" and the general formula is

7. Alcohols:

Alcohols (which we all associate with drinking) are like alkanes but have a OH as their functional group, meaning they are polar and therefore quite reactive. General formula is Cn H2n+2 O with standard alcohols and their suffix is "ol".


When we talk about alcohol we associate it with drinking, but only one alcohol (ethanol) is used for consumption. The rest are used in various other reactions such as making esters.


8. Amines:

9. Carbonyl Compounds:

Carbonyl Compounds are organic compounds with an C=O bond. They are many carbonyl compounds which are used in a variety of circumstances.

10. Ketones

11. Aldehydes

12. Carboxylic Acids

13. Amides (A2)

14. Acidchlorides (A2)


Glossary 

This part of the blog covers all the definitions I put in bold.

Hydrocarbon(s) - An compound consisting of both hydrogen and carbon, it may also have other elements attached to the carbon(s) such as oxygen, nitrogen (ammonia) and chlorine. All of organic chemistry evolves around hydrocarbons in one form or another.


Functional Group -


General Formula -