ORGANIC CHEMISTRY ICHEM 241aDr. Jeff PyunFall 2007

“An introduction to the chemistry of carbon, the brick of humanity.”-me

Bonding and Molecular Structure

e– pair molecularformula geometry geometry (angle)

C2H2

CH2O

CH4

HCN

NH3

H2O

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 TheoriesValence bond theory

sp3 hybridization

CH4 facts: tetrahedral,4 equivalent bondsC

H

HH

H

C2s

2ppromoteelectron 2p

2s

hybridize

sp3

hybrida.o.s

sp3 hybrid a.o.s:

C(sp3)tetrahedral (sp3

C + 1sH)

4HC

H

HH

H

Bonding TheoriesValence bond theory

sp3 hybridization

C N O

CN

HH

H

HH

CC

H

HH

H

HH C

OH

H

HH

(sp3C + sp3

C) (sp3C + sp3

N) (sp3C + sp3

O)

lone pairsin sp3 a.o.s

Bonding TheoriesValence bond theory

sp2 hybridizationC2H4 facts: all six atoms lie

in same planeC CH

H

H

H

trigonal planar = sp2

2psp2

C Csp2

2p

H1s 1s

H H1s 1s

H

C CH H

H H

2p

(sp2C + 1sH)

(sp2C + sp2

C)

overlapp orbitals C C

H H

H H

bond

all atoms coplanarfor p orbital overlap

= C C

H

H

H

H

double bond =1 bond +1 bond

Bonding TheoriesValence bond theory

sp2 hybridization

C O

(sp2C + sp2

C) + (sp2C + sp2

O) +

lone pairsin sp2 a.o.s

C CHH

HHC O

H

H

Bonding TheoriesValence bond theory

sp hybridization

C2H2 facts: linear = spH C C H

2psp

C Csp

2p

H1s 1s

H

C C HH

2p

(spC + 1sH)

(spC + spC)

C CH H

2 bonds

= C CH H

triple bond =2 bonds +1 bond

Bonding TheoriesValence bond theory

sp hybridization

N

(spC + spN) + 2

lone pairin sp a.o.

C NH

Bonding TheoriesValence bond theory

Lecture Activity - What is the hybridization of each indicated atom in the following compound?

17-ethynylestradiol(“The Pill”)

HO

CH3OH

C CH

Other Bonding TheoriesMolecular orbital theory: H2

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