Isomeric Alkanes

The molecular formulae for the C1 to C3 alkanes lead to single, unique structures.
However for C₄H₁₀, there are two possible constitutional isomers. It is important to be able to recognise isomers because there can have different chemical, physical properties and biological properties. The constitutional isomers of C₄H₁₀ are shown below along with some properties:
 

butane		Tm = -139oC  Tb = -0.4oC  DHf = -125.6 kJ/mol DHc = -2877 kJ/mol
methyl propane		Tm = -161oC  Tb = -10.2oC  DHf = -135.6 kJ/mol DHc =-2868 kJ/mol

For C₅H₁₂ has three possible constitutional isomers:
 

pentane		Tb    =   36.1 oC DHf = -147 kJ/mol DHc = - 3509 kJ/mol
methyl butane		Tb    =    30 oC DHf = -154.1 kJ/mol   DHc = -3502 kJ/mol
22dimethyl propane		Tb   =   9.5 oC DHf = -168.0 kJ/mol   DHc = -3493 kJ/mol