CHE 3331 Chapter Notes - Chapter 16: Thiophene, Bromine, Pyridinium
Document Summary
In 1866 friedrich kekul proposed a cyclic structure for benzene with three bonds: benezene"s structure is actually a resonance hybrid between two of these structures. Bond order = 1. 5 (so not really double bonds) Every bond is at a 120 degree angle. Each sp2 hybridized c in the ring has an unhybridized p orbital perpendicular to the ring which overlaps around the ring. The six pi electrons are delocalized over the six carbons. Annulene: cyclical hydrocarbons with alternating single and double bonds. Originally, all annulenes were proposed to be aromatic. Essentially the annulenes must be in a planer orientation for the p orbitals of the pi bonds to overlap (below) cyclooctatetraene is not planar. Cyclic structures of mos differ from linear mos: a two-dimensional cyclic system requires two- dimensional mos with the possibility of two distinct mos having the same energy.
