Question

Why is (E)-1,2-diisopropylethene more stable than (Z)-1,2-diisopropylethene? Why are they more stable than 1,1-diisopropylethe?

And doesn't the bond angle between the C=C-C carbons increase with (Z)-1,2-diisopropylethene > (E)-1,2-diisopropylethene > 1,1-diisopropylethe? So why isn't the same as (E) being greater than (Z)?

Answer 1

The E (trans-) isomer is usually more stable because it is a less crowded structure (less steric hindrance), and because attractive intermolecular forces involving the H's are more easily formed. Building molecular models of the two kinds of isomers would help you visualize this.