Match each alkene with its heat of combustion. The five available values (in kJ/mol) are: 5293, 4658, 4650, 4638, 4632. (a) 1-Heptene (b) 2,4-Dimethyl-1-pentene (c) 2,4-Dimethyl-2-pentene (d) 4,4-Dimethyl-2-pentene (e) 2,4,4-Trimethyl-2-pentene Which assignment is correct?

Question

Accepted Answer

a-4658, b-4638, c-4632, d-4650, e-5293. 2,4,4-Trimethyl-2-pentene is C8H16, the largest molecule, so it has by far the highest heat of combustion: 5293 kJ/mol (e). The remaining four are C7H14 isomers, distinguished only by stability. Less-substituted/more-strained alkenes are less stable and release MORE heat on combustion. 1-Heptene (a, monosubstituted) is the least stable C7 -> highest of the C7 group, 4658. 4,4-Dimethyl-2-pentene (d, disubstituted but with a bulky tert-butyl group) -> 4650. 2,4-Dimethyl-1-pentene (b, terminal disubstituted) -> 4638. 2,4-Dimethyl-2-pentene (c, trisubstituted, most stable) -> lowest, 4632.

Match each alkene with its heat of combustion. The five available values (in kJ/mol) are: 5293, 4658, 4650, 4638, 4632. (a) 1-Heptene (b) 2,4-Dimethyl-1-pentene (c) 2,4-Dimethyl-2-pentene (d) 4,4-Dimethyl-2-pentene (e) 2,4,4-Trimethyl-2-pentene Which assignment is correct?

Solution

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