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.
This is a picture of the compound showing all of the bonds present in the compound. An example is ethane:
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:
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:
Longest Carbon Chain Prefix
Rules for Naming Alkanes
The parent name of the molecule is determined by the number of carbons in the longest chain.
In the case where two chains have the same number of carbons, the parent is the chain with the most substituents.
The carbons in the chain are numbered starting from the end nearest the first substituent.
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.
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.
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 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.
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.
Numbering of the substituent chain starts from the carbon attached to the parent chain.
The entire name of the branched substituent is placed in parentheses, preceded by a number indicating which parent-chain carbon it joins.
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).
An empirical formula is a formula in which the minimal ratio of all the constituents of each compound is written in the formula. In order to change an empirical formula to a molecular formula the ratio between the molecular weight and the empirical weight would be found and then the empirical formula would be multiplied with this ratio.
- Start with the number of grams of each element, given in the problem.
If percentages are given, assume that the total mass is 100 grams so that
the mass of each element = the percent given.
- Convert the mass of each element to moles using the molar mass from the periodic table.
- Divide each mole value by the smallest number of moles calculated.
- Round to the nearest whole number. This is the mole ratio of the elements and is represented by subscripts in the empirical formula.
If the number is too far to round (x.1 ~ x.9), then multiply each solution by the same factor to get the lowest whole number multiple.
e.g. If one solution is 1.5, then multiply each solution in the problem by 2 to get 3.
e.g. If one solution is 1.25, then multiply each solution in the problem by 4 to get 5.
Hybridisation is the concept of mixing orbitals to form new hybrid orbitals which would allow different orientations to take place in order to be able to produce the greatest possible angles between different bonds.
An atom that can be used to show different types of hybridisation is C, since this can produce three different hybrid orbitals, mainly sp3, sp2 and sp.
The ground state of C is: The excited state of C is:
In an sp3 hybridisation the four orbitals would then recombine to form 4 new hybrid orbitals, which can then rearrange to form a tetrahedron. this can be seen as follows:
In an sp2 only three orbitals are hybridised while the last p orbital would remain unchanged, producing a planar compound with a perpendicular orbital. This can be seen as follows:
In an sp hybridised orbital the hybridisation occurs only between an s orbital and one of the 3 p orbitals producing two sp hybrid orbitals and leaving two p orbitals. This can be seen as follows: