The relative stabilities of a set of alkene isomers can be quantified using diff
ID: 1042333 • Letter: T
Question
The relative stabilities of a set of alkene isomers can be quantified using different approaches. In class we used the heat of formation, but the heat of combustion may also be used. (Note that combustion is an exothermic reaction.) Match each alkene with its appropriate heat of combustion by writing the letter corresponding to each alkene on the line under its heat of combustion 1-Heptene A. B. 2,4-Dimethyl-1-pentene C. 2,4-Dimethyl-2-pentene D. (Z)-4,4-Dimethyl-2-pentene E. 2,4,4-Trimethyl-2-pentene AHcombustion values (kcal/mol) 1264.9 1113.4 1108.6 1107.1 2. The sex attractant of the Meditteranean fruit fly is (E)-6-nonen-1-ol. Draw the Lewis structure for this compound, showing appropriate stereochemistry at the double bond The sex attractant of the codling moth is the 2Z, 6E isomer of this compound CH3(CH2)2C(CH3)-CHCH2CH2C(CH2CH3)-CHCH2OH Draw the Lewis structure for this compound, showing appropriate stereochemistry at the double bonds 4.Which is the more stable alkene? Circle it and explain your reasoning briefly Bicyclo[4.2.0]oct-7-ene Bicyclo[4.2.0]oct-3-eneExplanation / Answer
Heat combustion decreases with increasing stability of compounds.
generally stability of alkene increases with number of hyperconjugating hydrogens.
but among the given alkene Z-4,4-Dimethyl-2-pentene is least stable because of steric hindrance between two bulky groups , hence it has highest heat of combustion.
so, for the given alkenes decreasing order of stability is
2,4-dimethyl-2-pentene (seven hyperconjugating hydrogen) > 2,4,4-trimethyl-2-pentene (six hyperconjugating hydrogen) > 1-Heptene (2 hyperconjugating hydrogen) > 2,4-dimethyl-1-pentene (one hyper conjugating hydrogen) > Z-4,4-Dimethyl-2-pentene .
hence, heat of combustion of the alkenes are
Z-4,4-Dimethyl-2-pentene = -1264.9 Kcal/mole
2,4-dimethyl-1-pentene = -1113.4 Kcal/mole
1-Heptene = -1111.4 Kcal/mole
2,4,4-trimethyl-2-pentene = -1108.6 Kcal/mole
2,4-dimethyl-2-pentene = -1107.1 kcal/mole