Page 275 - Advanced Organic Chemistry Part A - Structure and Mechanisms, 5th ed (2007) - Carey _ Sundberg

256 3.1.1. Relationship between Structure and Thermodynamic Stability
for Hydrocarbons
CHAPTER 3
Structural Effects on Extensive thermodynamic data are available for the major classes of hydro-
Stability and Reactivity
carbons. Table 3.1 gives data for the C −C and C alkanes and the C −C alkenes,
4 6 8 4 6
and several general relationships become apparent. One is that chain branching
increases the stability of alkanes. This relationship is clear, for example, in the data
for the C alkanes, with a total enthalpy difference of nearly 4 kcal/mol between
6
the straight-chain hexane and the tetra-substituted 2,2-dimethylbutane. There is a
similar range of 4.5 kcal/mol between the least stable (octane) and most stable

Table 3.1. Standard Enthalpy of Formation of Some Hydrocarbons
(in kcal/mol) a
Alkanes (liquid)

C 4 C 8
Butane −35 0 Octane −59 8
2-Methylpropane −36 7 2-Methylheptane −60 9
3-Methylheptane −60 3
4-Methylheptane −60 1
C 5
Pentane −41 5 2,2-Dimethylhexane −62 6
2-Methylbutane −42 7 2,3-Dimethylhexane −60 4
2,2-Dimethylpropane −45 5 2,4-Dimethylhexane −61 4
2,5-Dimethylhexane −62 2
3,4-Dimethylhexane −60 2
C 6
Hexane −47 5 3,3-Dimethyhexane −61 5
2-Methylpentane −48 9 2,2,3-Trimethylpentane −61 4
3-Methylpentane −48 4 2,2,4-Trimethylpentane −62 0
2,3-Dimethylbutane −49 6 2,3,4-Trimethylpentane −60 9
2,2-Dimethylbutane −51 1 2,3,3-Trimethylpentane −60 6
3-Ethyl-2-methylpentane −59 7
3-Ethyl-3-methylpentane −60 4
2,2,3,3-Tetramethylbutane −64 3
B. Alkenes (liquid)
C 4 C 6
1-Butene −4 90 1-Hexene −17 7
E-2-Butene −7 89 E-2-Hexene −20 4
Z-2-Butene −7 10 Z-2-Hexene −20 1
2-Methylpropene −8 96 E-3-Hexene −20 6
Z-3-Hexene −18 9
2-Methyl-1-pentene −21 5
C 5
1-Pentene −11 2 3-Methyl-1-pentene −18 7
E-2-Pentene −13 9 4-Methyl-1-pentene −19 1
Z-2-Pentene −12 8 2-Methyl-2-pentene −23 5
2-Methyl-1-butene −12 3 3-Methyl-2-pentene −22 6
3-Methyl-1-butene −16 4 E-3-Methyl-2-pentene −22 6
Z-3-Methyl-2-pentene −22 6
E-4-Methyl-2-pentene −21 9
Z-4-Methyl-2-pentene −20 8
2,3-Dimethyl-1-butene −22 3
3,3-Dimethyl-1-butene −20 9
2-Ethyl-1-butene −20 8
3,3-Dimethyl-1-butene −20 9
2,3-Dimethyl-2-butene −24 3
a. From Thermochemical Data of Organic Compounds, 2nd Edition, J. B. Pedley, R. O. Naylor,
and S. P. Kirby, Chapman and Hall, London, 1986.