Understanding Organic Chemistry




Introduction: Understanding Organic Chemistry

About: "But I being poor have only my dreams, spread out beneath your feet. Tread softly because you tread on my dreams" 1st Cleric Preston, Equilibrium QED

The Aim of this instructable is to give a light overview of Organic chemistry including; Formulae, structure and identification to aid anyone who is interested in or is taking this subject.

Organic Chemistry is a subsect of chemistry which involves organic substances and their properties, structures and compositions.  The substances contained in the subject can have Hydrogen, Oxygen, Nitrogen, Sulfur, the Halogens and a variety of other molecules contained in their molecular formulae.

It is important to distinguish between Organic and Inorganic chemistry as there are carbon containing substances that are regarded as "inorganic", such chemicals and ions include;
- Carbonates (CO3 [2-])
- Hydrogen Carbonates (HCO3 [-])
- Oxides of Carbon (CO, CO2)
- Cyanos and nitriles (CN [-])
Apart from these few (plus a few more not listed) most other carbon containing compounds are organic.

By the end of this instructable you should be able to name and identify the molecule shown below

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Step 1: Hydrocarbons

Hydrocarbons are a set of organic compounds which contain only Hydrogen and Carbon (as the name implies).  This set of chemicals are very important in understanding organic chemistry and come in a variety of different forms.
In inorganic chemisty the combination of 2 different element generally produces only 1, 2 or 3 different molecules but in organic chemistry the combination of just Carbon and Hydrogen can produce MILLIONS of different molecules!
For ALL hydrocarbons there is a general molecular formula this is;
"CxHy" where x and y are the amounts of carbon and hydrogen respectively
Another rule all hydrocarbons obey is that any carbon atom must have four bonds to fill its outer shell (it has four valence electrons) this can be done by using Hydrogen atoms or by using double or even triple bonds between cabon atoms.
The simple fact that there are so many different hydrocarbons means that a standardised form of identifying them is necessary, this is called the IUPAC (International Union of Pure and Applied Chemistry) nomenclature; (Refer to image one)

Step 2: Aliphatic HCs

So what are aliphatic hydrocarbons?
Aliphatic refers to the fact that there are no aromatic rings, put simply they all have straight chains.
There are three subsects of aliphatic hydrocarbons, these include;
- Alkanes
- Alkenes and
- Alkynes

Alkanes have the molecular formula of "CnH2n+2" which means for every carbon molecule there are two hydrogens plus two more.  For example when there is one Carbon there are four hydrogens, this molecule is known as "Methane"
All Alkanes are "Saturated" which means that the bonds between all of the Carbon atoms are single (using only 2 electrons) this is represented by a line between them.  Most people have heard of the term "saturated" namely on brands of cooking oil which include unsaturated, monounsaturated and polyunsaturated.  In this case "unsaturated" refers to compounds that contain one (mono) or more (poly) double or triple bonds (shown as 2 or 3 lines respectively).

So now we know the basics lets see the first molecule measured by it having only one carbon atom; (see image one) This moleculeis called methane with a prefix of Meth- (meaning one carbon) and a suffix of -ane (meaning it is an alkane)
The next image (2) is of ethane the next alkane, and after that in image 3 is propane as you may have noticed because they are both alkanes the suffix hasn't changed but as the number of carbon atoms increases the prefix changes.
This is a list of the prefixes representing the number of carbon atoms there are in a hydrocarbon;
1 Meth-ane
2 Eth-ane
3 Prop-ane
4 But-ane
5 Pent-ane
6 Hex-ane
7 Hept-ane
8 Oct-ane
9 Non-ane
10 Dec-ane

Step 3: Alkenes and Alkynes

Alkenes are a set of unsaturated compounds which contain one double bonded carbon atom.
The molecular formula for all alkenes is CnH2n where put simply the number of hydrogen atoms is double that of the carbon atoms.  The first alkene is not methene as we would expect but it is ethene (1), this is because it must have a double bond and this requires two or more carbon atoms.  As with the alkanes they follow the same set of prefixes so the next in the series would be propene (2).

But what happens if we go to the next one butene?  Well we have two places to put the double bond, one in the centre and one near the end!  This is called structural isomerism and because of this we have two structural isomers of butene.

To show where the double bond (or triple in an alkyne) is, you number the longest chain of carbon atoms containing the double bond while making sure the double bond is "touching the smallest number".  For image number three the lowest number the double bond touches is 2 so we would write it as "but-2-ene" (be sure to put the "-" between all numbers and letters)

Alkynes are basically alkenes but the double bond is a triple bond with an accepted molecular formula of CnHn-2, which is two less than an alkene (noticing the trend?)
Image number (4) shows what would be called "Ethyne" but is commonly known as "acetylene"

Step 4: Branches on an Aliphatic HC

This segment tries to explain what happens if there is one or more "branches" coming off of a straight chain hydrocarbon, how to draw them and how to identify them.Branches can come off of any aliphatic hydrocarbons such as Alkane, Alke... (you know the rest!).  The most simple branch that comes off of a straight chain hydrocarbon belongs to the Alkyne group and if you can remember back to the prefixes it is "Methyl".  For an alkane to have a distinguishable branch it must be coming off of the longest carbon chain for example; (1) 2-Methylpropane which has a methyl branch on its second carbon on the longest chain.  It is important to remember that the longest chain isn't just the obvious, the longest chain is 3 but this is not necessarily left to right!
You could create the chain from the left carbon to the middle carbon to the bottom carbon!
Just be wary of this when you ever do any complex questions.

A branch is not just limited to methyl it can also include ethyl, propyl and so on and so forth ad infinitum.

Step 5: Aromatic HC

Aromatic hydrocarbons are cyclic in nature meaning that both ends meat up and bond to form a round shape.  Aromatics have a molecular formula of CnHn, it is important to understand why this isnt CnH2n where each carbon would bond to the two neighbouring carbons and to two hydrogens.  The reason it is CnHn is because each carbon atom releases an electron into the centre of the ring, this can also be shown as alternating single and double bonds.  But either way the effect is that each carbon only has one hydrogen or free single bond.  The attached image is that of "Toleune" Which is the chemical; CycloHexane with a methyl branch.  Confusingly CycloHexane is commonly known as Benzene (AKA Benzene ring/s)

As seen in the image cyclic hydrocarbons branch in a similar way to aliphatic HCs and have the same numbering system although the double bond in an cycloalkene is always one.
Also you could have a massive chain coming off of the cyclic part without it influencing the "end" name for example;  decthylcyclopropane

Step 6: Alicyclic HCs

Alicyclic HCs are very similar to aromatic HCs the difference being that alicyclic compounds don't have the electron sharing '"ring" in the centre of the molecule so rather than a molecular formula of CnHn they have a formula of;
CnH2n for Alkanes
CnH2n-2 for Alkenes
- CnH2n-4
for Alynes
The reason why they have 2 less hydrogen atoms in their formula is because the ends are tied to each other using up 2 single bonds!
The attached images are of the different Alicyclic groups in a cyclic but(suffix), the first being; cyclic propane the second; cyclic propene and the third; cyclic propyl.

Step 7: Identifying an Aliphatic HC

Identify the longest continuous carbon cain containing the double bond (if it is an Alkene).  This is the "parent" chaing.  It is given the stem name associated with the number of carbon atoms in this chain with the suffix added by the type of Aliphatic HC.
In this example the double bond is on the second carbon and there are 7 carbon atoms in the stem chain therefore the ending will be called; "Hept-2-ene"

Name the branches and remember their carbon number, if there are multiple branches which are the same there is a different writing style.  In the example there are two methyl branches so instead of writing; 5-Methyl-6-Methyl we write "5,6-Dimethyl"

Add the two names together and check over to see if your answer is plausable;
 Also you would add the structural isomerism; TRANS (see next page) to give;
"TRANS 5,6-DimethylHept-2-ene"

Step 8: Geometric Isomerism

Geometric isomerism is a way of differenciating Hydrocarbons by the positioning of their branches and hydrogen about a double bond.  If you notice image number one you will see that each hydrogen is on the opposite side of the molecule this geometric isomer is TRANS.
The opposite geometric isomer is (you guessed it) CIS which means the two hydrogens are on the same side.
In summary;
TRANS = opposite
CIS = same

Step 9: Conclusion and Questions

This may be the end of the instructable but the subject goes on and on, if I had the time I would go into Halogenation, substitution and addition reactions and whatnot but this is sufficient for you to get a general idea of what Organic chemistry encompasses.
I hope you found this helpful and for more information just browse Wikipedia.org which has a large and succinct database on organic chem.

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    11 Discussions


    6 years ago on Introduction

    Sorry to seem picky, but it is not correct to capitalise the parent hydrocarbon in names like 5,6-dimethylhept-2-ene. And what on earth is decthylcyclopropane ? Did you mean decylcyclopropane ? The fourth bonding electron of the carbon atoms in benzene is not " released into the centre of the ring ", it is contained in a set of bonding molecular orbitals which are located around the circumference of the ring.


    8 years ago on Introduction

    I like that you want to introduce people to chemistry, and try to make them understand the names given to these molecules, but this isn't a guide to understanding organic chemistry. A better name would probably be: 'explanation of the nomenclature of easy hydrocarbons' but that would probably scare of most people on this site, and the rest probably knows about it already :p


    9 years ago on Step 5

    Just a quick correction, benzene is not the same thing as cyclohexane. Benzene has a formula of C6H6 while cyclohexane has a formula of C6H14. Oh, and toluene is benzene with a methyl branch, not cyclohexane with a methyl branch.


    10 years ago on Introduction

     It's a nice overview of the nomenclature of organic compounds, but that's not, in itself, "organic chemistry".  Perhaps the title is a bit misleading, but I think it would be good for high school or introductory organic chemistry students as a reference to naming this stuff.


    10 years ago on Introduction

    Where does "cyclic hexane" come from? Cyclohexatriene surely?



    Reply 10 years ago on Introduction

    Sorry for the typo it should be CycloHexane
    Ill just fix that up...


    Reply 10 years ago on Introduction

    Since you went this far, how about adding stereoisomerism - Alanine would do it as an example?



    Reply 10 years ago on Introduction

    If I was to do that I would also add in halogenation reactions (probably refering to the synthesis of tetrachloromethane).  But at the moment I have alot on my plate (exams) and that's why I was querying anyone if they wanted it to become a collaboration.


    10 years ago on Introduction

    As a former organic chem student, I would find this quite useful as a "cheat sheet" or revision/reference material, but perhaps less so for explaining the subject.  It's got plenty of facts, but doesn't actually explain much of the detail.  For example, you reference structural isomerism of butene but don't go on to explain the structures of but-1-ene and but-2-ene and their different properties, or indeed exactly what "isomer" means.

    I'd read more of these if you wrote them, if only because I enjoy making people think I have magic powers by reading IUPAC systematic names and decoding them :)

    I only noticed one obvious typo, you give the formula of alkanes as CnHn+2 where it should be CnH2n+2.


    Reply 10 years ago on Introduction

    Do you reckon it would be a good idea to make this a collaboration?
    That way we could all improve the instructable in the areas we see are lacking...


    Reply 10 years ago on Introduction

    It's text-book stuff, but since I wouldn't think Tombini would have copied it out of a text book it's well presented. E / Z bond configuration is more interesting, stereoisomerism etc....