Alkene Stability
Saytzeff’s Rule: the more highly substituted an alkene is, the more stable it is. In other words, alkyl groups attached to the double bonded carbons stabilize the alkene.
The two probable factors responsible for the stabilizing effect of alkyl groups to the double bond are the contribution of electron density to the pi bond by the alkyl groups, and the increased separation of bulky groups from one another (120o bond angle) in alkenes.
In general, trans isomers are more stable than cis isomers because of decreased steric interactions.