Lecture 23 Content: Equally Weighted Contributors Ozone: Three resonance structures of ozone are drawn with the double bond alternating between the oxygen atoms. Formate: Two resonance structures of formate are drawn with the double bond alternating between the carbon and one of the oxygen atoms. Unequally Weighted Contributors Carboxylic Acid: Two resonance structures are drawn. The first structure shows a double bond between the carbon and one of the oxygen atoms, while the second structure shows a single bond between the carbon and that oxygen and a double bond between the carbon and the other oxygen. The first structure is labeled as "heavily weighted." Ester: Two resonance structures of an ester are drawn, similar to the carboxylic acid structures. The first structure is labeled as "heavily weighted." Amide: Two resonance structures of an amide are drawn. The first structure shows a double bond between the carbon and the oxygen and a single bond between the carbon and the nitrogen. The second structure shows a single bond between the carbon and the oxygen and a double bond between the carbon and the nitrogen. The first structure is labeled as "heavily weighted." General Instructions Draw all e- in to get zero formal charges. Lewis dot structure See if another "can" be made (LP next to π bond) Carbon Dioxide Core: 1s² C: sp² + 2p orbitals on each O 2 bonds, 2 LP πe- on all 3 O πe- on outer 2 O, node on middle Other Notes 2 delocal. e- systems π LUMO - ability to be Lewis acid* π HOMO - ability to be Lewis base* C-O stretch: 1600 cm⁻¹ delocal. e- density → π → ↓* Butadiene Description: Butadiene is a molecule with two double bonds that are adjacent (conjugated). Structure: A Lewis structure of butadiene is drawn, showing the four carbon atoms connected by single and double bonds. Core: 1s² Hybridization: sp² 1 p orbital on each C 9 bonds, 4 delocalized electrons 4 p orbitals 8 electrons Conjugated π Systems Description: Conjugated π systems have alternating single and double bonds, allowing for delocalization of electrons. π bonds are weaker than double bonds due to delocalization ↑ thermodynamic stability, ↑ kinetic reactivity Easier HOMO access Diagrams: Several diagrams illustrate the molecular orbitals of butadiene, ethene, and 1,3-butadiene. The diagrams show the energy levels of the molecular orbitals and the distribution of electrons within them. Labels indicate the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) in each case.