ORGANIC CHEMISTRY I CHEM 241a Dr. Jeff Pyun Fall 2007 “An introduction to the chemistry of carbon, the brick of humanity.” -me

Bonding and Molecular Structure e – pair molecular formula geometry geometry (angle) C 2 H 2 CH 2 O CH 4 HCN NH 3 H 2 O

Atomic Structure: Orbitals Quantum mechanics: describes electron energies and “locations” by a wave equation –Wave function solution of wave equation –Each Wave function is an orbital,  A plot of  2 describes where electron most likely to be Electron cloud has no specific boundary so we show most probable area

Shapes of Atomic Orbitals for Electrons Four different kinds of orbitals for electrons based on those derived for a hydrogen atom Denoted s, p, d, and f s and p orbitals most important in organic chemistry s orbitals: spherical, nucleus at center p orbitals: dumbbell-shaped, nucleus at middle

p-Orbitals In each shell there are three perpendicular p orbitals, px, py, and pz, of equal energy Lobes of a p orbital are separated by region of zero electron density, a node

Bonding Theories Valence bond theory sp 3 hybridization CH 4 facts: tetrahedral, 4 equivalent bonds

Bonding Theories Valence bond theory sp 3 hybridization

Bonding Theories Valence bond theory sp 2 hybridization C 2 H 4 facts: all six atoms lie in same plane trigonal planar = sp 2

Bonding Theories Valence bond theory sp 2 hybridization

Bonding Theories Valence bond theory sp hybridization C 2 H 2 facts:linear = sp

Bonding Theories Valence bond theory sp hybridization

Bonding Theories Valence bond theory Lecture Activity - What is the hybridization of each indicated atom in the following compound? 17-ethynylestradiol (“The Pill”) HO CH 3 OH CCH

Other Bonding Theories Molecular orbital theory: H 2 H + H  H—H Two electrons in  1s are lower energy than in the separate atoms  covalent bond

Molecular Orbitals in Ethylene The  bonding MO is from combining p orbital lobes with the same algebraic sign The  antibonding MO is from combining lobes with opposite signs Only bonding MO is occupied

Ionization of valence electrons in methane shows 2 different types of bonds!

Molecular Orbital Diagram of Methane