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Because of the versatility in the ways atoms of carbon bond, it is common to find different molecular structures of alkanes (and alkenes & alkynes) for the same chemical formula. We call this phenomena structural isomerism and we call the different structures isomers. It is important to understand that 2 or more structural isomers (with the same chemical formula) are different compounds. Different isomers with the same chemical formula will have different properties (such as melting point and reactivity).
At this point one may ask, "How do we indicate different isomers with the same chemical formula?" and the answer is, "By using the proper names of the isomers.". For simple chain alkanes, the lowest number of carbon atoms of which 2 or more isomers exist is '4'. This is explained in the following diagram.
Note the use of the prefix, "iso-". An iso group is always on the central carbon of an odd-number carbon chain. The iso- group has the effect of dividing the chain into two equal halves. Note, also, that the second name (methylpropane) does not have a number indicated the position of the methyl group on the propane chain. This is because the methyl group can only be attached to the number 2 carbon of the propane chain. Alkyl groups (e.g., methyl, ethyl) cannot be attached as a side chain to a terminal carbon atom of an alkane. The result is simply to increase the length of the chain.
That's all for now. As always, thank you for reading!
A Publication of http://ExcellenceInLearning.biz
Because of the versatility in the ways atoms of carbon bond, it is common to find different molecular structures of alkanes (and alkenes & alkynes) for the same chemical formula. We call this phenomena structural isomerism and we call the different structures isomers. It is important to understand that 2 or more structural isomers (with the same chemical formula) are different compounds. Different isomers with the same chemical formula will have different properties (such as melting point and reactivity).
At this point one may ask, "How do we indicate different isomers with the same chemical formula?" and the answer is, "By using the proper names of the isomers.". For simple chain alkanes, the lowest number of carbon atoms of which 2 or more isomers exist is '4'. This is explained in the following diagram.
Note the use of the prefix, "iso-". An iso group is always on the central carbon of an odd-number carbon chain. The iso- group has the effect of dividing the chain into two equal halves. Note, also, that the second name (methylpropane) does not have a number indicated the position of the methyl group on the propane chain. This is because the methyl group can only be attached to the number 2 carbon of the propane chain. Alkyl groups (e.g., methyl, ethyl) cannot be attached as a side chain to a terminal carbon atom of an alkane. The result is simply to increase the length of the chain.
That's all for now. As always, thank you for reading!
A Publication of http://ExcellenceInLearning.biz