Transoid Diene / Heteroannular diene / linear diene: This type of diene generally involves the attachement of two trans dienes together. Since the two double bonds attached are trans, it leads to a linear diene which is also called a heteroannular diene as the diene cannot be placed within one ring system as it would cause the ring to become very unstable (5 – 6 carbon rings are most stable with very few exceptions). The base value for a heteroannular diene system is 215 nm according to the Woodward-Fieser rules. Examples of heteroannular dienes are shown below.