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

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