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Straight Chain And Branched Alkanes

Butane (C4H10) and the other alkanes above it can exhibit constitutional isomerism. If the alkane is unbranched and has a straight chain, it is called n-alkane.
For example, the straight chain pentane is called n-Pentane.


n-Pentane CH3CH2CH2CH2CH3

n-Butane CH3CH2CH2CH3


Constitutional (structural) isomers are isomers with the same molecular formula, but are different in terms of the order in which the atoms are connected.


Butane has two possible isomers: n-Butane and Isobutane

image\Ch 15 Sec D first graphic.png

Pentane has three isomers: n-Pentane, Isopentane, and neopentane

image\Ch 15 sec D 2nd graphic.png

The only way to find the number of possible isomers is by drawing out the structures sequentially and systematically, starting from the straight chain compound. There is no simple general formula to calculate the number of possible isomers of an alkane.

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