The energy difference between cis- and trans-but-2-ene is about 4 kJ/mol; however, the trans isomer of 4,4-dimethylpent-2-ene is nearly 16 kJ/mol more stable than the cis isomer. Explain this large difference.

A double bond in a six-membered ring is usually more stable in an endocyclic position than in an exocyclic position. Hydrogenation data on two pairs of compounds follow. One pair suggests that the energy difference between endocyclic and exocyclic double bonds is about 9 kJ/mol. The other pair suggests an energy difference of about 5 kJ/mol. Which number do you trust as being more representative of the actual energy difference? Explain your answer.

Predict the products of E1 elimination of the following compounds. Label the major products.

(a)

For each alkene, indicate the direction of the dipole moment. For each pair, determine which compound has the larger dipole moment.

c. cis-1,2-dibromo-1,2-dichloroethene or cis-1,2-dichloroethene

For each alkene, indicate the direction of the dipole moment. For each pair, determine which compound has the larger dipole moment.

a. cis-1,2-difluoroethene or trans-1,2-difluoroethene

For each alkene, indicate the direction of the dipole moment. For each pair, determine which compound has the larger dipole moment

b. cis-1,2-dibromoethene or trans-2,3-dibromobut-2-ene

Predict the products of E1 elimination of the following compounds. Label the major products.

(c)