Introduction to Organic Compounds

Introduction

The  basis  of  Organic  Chemistry  is  the  fact  that  Carbon  molecules  can  produce  long  chains  which  can produce a number of different molecules. The reason why Carbon is such an ideal building block is due to following reasons:

• Carbon-Carbon bonds are very strong.
• Carbon can bond with 4 different other atoms.
• Can produce single, double and triple bonds.
• Has a very similar electronegativity to Hydrogen, making a hydrocarbon chain highly unreactive.

Drawing an organic compound

There are several ways to draw an organic compound, mainly being display formulae, 3D structure and skeletal structure.

Display formulae

This is a picture of the compound showing all of the bonds present in the compound. An example is ethane:

3D structure

Simple organic chains can be drawn as a 3D structure, by using the following convention:

which can thus show the orientation of the molecule. Ethane in 3D would be shown as follows:

Structural formula

A structural formula is normally used for long chained chains, in which only the Carbons are drawn and any functional groups that are attached to the chain. Butan-2-ol would be drawn as follows:

Naming of alkanes

When naming a carbon chain it is of utter importance to note the longest Carbon chain. This would be the basis of the naming and the prefixes are as follow:

Number of Carbons	Prefix	Functionality	Suffix
1	meth-	alkane	-ane
2	eth-	alkene	-ene
3	prop-	alkyne	-yne
4	but-	alcohol	-anol
5	pent-	halogenoalkanes	halogeno-prefix-ane
6	hex-	carboxylic acid	-anoic acid
7	hept-	aldehydes	-anal
8	oct-	ketones	-anone
9	non-	acid anhydrides	-anoic anhydride
10	dec-	acid chlorides	anoic chloride
		nitriles	-ane nitrile
		amines	amino-prefix-ane

If there are side groups the name of the group might need to be tweaked. This will eb written as seen in the table below.

Substituent	Name Change
Carbon Chain	alkyl-
Chlorine	chloro-
Bromine	bromo-
Iodine	iodo-
Alcohol	hydroxy-

Rules for Naming Organic Compounds

Simple Alkanes

1. Determine the main functionality of the compound.
2. The parent name of the molecule is determined by the number of carbons in the longest chain.
3. In the case where two chains have the same number of carbons, the parent is the chain with the most substituents.
4. The carbons in the chain are numbered starting from the end nearest the first substituent.
5. In the case where there are substituents having the same number of carbons from both ends, numbering starts from the end nearest the next substituent.
6. When more than one of a given substituent is present, a prefix is applied to indicate the number of substituents. Use di- for two, tri- for three, tetra- for four, etc. and use the number assigned to the carbon to indicate the position of each substituent.

Branching

1. Branched substituents are numbered starting from the carbon of the substituent attached to the parent chain.  From this carbon, count the number of carbons in the longest chain of the substituent. The substituent is named as an alkyl group based on the number of carbons in this chain.
2. The numbering of the substituent chain starts from the carbon attached to the parent chain.
3. The entire name of the branched substituent is placed in parentheses, preceded by a number indicating which parent-chain carbon it joins.
4. Substituents are listed in alphabetical order. To alphabetize, ignore numerical (di-,  tri-, tetra-) prefixes  (e.g., ethyl would come before dimethyl),  but don’t ignore don’t ignore positional prefixes such as iso and tert (e.g., triethyl comes before tertbutyl).

Cyclic Alkanes

The parent name is determined by the number of carbons in the largest ring (e.g., cycloalkane such as cyclohexane).

In the case where the ring is attached to a chain containing additional carbons, the ring is considered to be a substituent on the chain.  A  substituted ring that is a substituent on something else is named using the rules for branched alkanes.

When two rings are attached to each other, the larger ring is the parent and the smaller is a cycloalkyl substituent.

The carbons of the ring are numbered such that the substituents are given the lowest possible numbers.

Isomerism

Isomerism  is  a  phenomenon  were  different  molecules  having  the  same  molecular  formula  can  be produced,  with  the  most  important  isomerism  being  functional  isomerism.  This  would  mean  that  the molecule would have the same number of atoms, but these would be positioned in a different order, for example:

where the two molecules have got the same number of Carbon and Hydrogen atoms but the way the

Carbons are attached to each other is in a different order. This is called Chain isomerism.

A different type of functional isomerism  is when another functional group is present, which might be positioned on a different Carbon. An example would be:

where the Bromine is found on a different Carbon. This is called position isomerism.