University Of PennsylvaniaCollege of General Studies

Professor William A. Price, Ph.D.

CHEM 241-601

Organic Chemistry, 9th Edition

By T.W. Graham Solomons

From the Bark of the Pacific Yew Tree

O

NHO O

OH

O

O

O

OH O

O

OH

OO

O

Taxus brevifolia

Introduction: Structure and Bonding

Atomic structure

Lewis Structures

Resonance

Structural Formulas

Acids and Bases

Nucleus is a Tiny Fraction of the Volume of an Atom

Orbitals are Probabilities

2s Orbital Has a Node

The p Orbital

px, py, pz

Electron Configurations

Lewis Dot Structure of Methane

C...

.

carbon - 4 valence e hydrogen - 1 valence e

H.

1s22s22p2 1s

Tetrahderal Geometry

Bonding Characteristics of Period 2 Elements

“Saturated” with Hydrogen

All Have the Same GeometryAll Have 4 Regions of Electron Density

A Saturated Hydrocarbon

Nitromethane

Nitromethane has 2 Formal Charges

CH3NO2 C N

O

O

H

HH

Formal Charge = [Group #] - [# bonds] - [# non-bonding electrons]

N = 5-4-0 = +1

O = 6-1-6 = -1

Both Resonance Structures Contribute to the Actual Structure

CH3NO2

C N

O

O

H

H

HHH

H

N

O

O

C

2 Equivalent Resonance Structures

Resonance Rules

• Cannot break single (sigma) bonds

• Only electrons move, not atoms

3 possibilities:– Lone pair of e- to adjacent bond position

• Forms bond

bond to adjacent atom

bond to adjacent bond position

Curved Arrow Formalism Shows flow of electrons

C N

O

O

H

H

HHH

H

N

O

O

C

Arrows depict electron pairs moving

Resonance Stabilization of IonsPos. charge is “delocalized”

CH

HC

C

H

H

H

C

C

H

H

H

H

HC

H

HC

H

H

H

CC

resonance hybrid

Bonding Pattens for C, N, and Osp3 sp2 sp

C CC

C

N N N

O O

tetrahedral geometry trigonal planar linear

Common Cationic, Neutral and Anionic Forms

Two Nonequivalent Resonance Structures in Formaldehyde

Resonance in Acetate Anion

Resonance in [CH2NH2]+

Propose Lewis Structures

a) H2CO2 b) O3 c) N2O

d) NH3O e) C2H3ClO f) C2H5NO 

Problem

Draw [NO2]+ and [NO2]-. Which ion has a “localized” charge and which has a “delocalized” charge. Explain.

Drawing Structures

CC

CC

H

H

H

H

HH H

HH

H

Butane, C4H10

CC

C

C

H

H H

HH

H H

HHH

Methylpropane, C4H10

CH3CH2CH2CH3 CH3CH(CH3)CH3

Octane Representations

CC

CC

CC

CC

H

HH

H H

H H

H H

H H

H H

HHH

HH

CH3CH2CH2CH2CH2CH2CH2CH3

CH3(CH2)6CH3

Lewis structure condensed structural formula

C8H18 is molecular formula but there are 18 possible structural isomers

Condensed Formulas

Line-Angle Structures are Often Used as a Short-hand

Line-angle or "zig-zag" structures

Lewis structure

CC

CC

CC

CC

H

HH

H H

H H

H H

H H

H H

HHH

HH

Line-Angle Structures

CC

CC

CC

C

CC

C

CC

HH

H

H

H

H

H HH

H H

H

H

H

H

H

HH

HH

H

H H

HH

H

HH

H

H

H

H

H HH

H H

H

H

H

H

H

HH

HH

H

H H

HH

H

C12H26

HH

H

H

H

H

H HH

H H

H

H

H

H

H

HH

HH

H

H H

HH

H

At the end of every line and at the intersection of any lines there is a carbon atom with 4 bonds. Hydrogen atoms

are mentally supplied to fill the valency to 4.

Line-Angle structure Superimposed on Lewis Structure

CC

CC

CC

C

CC

C

CC

HH

H

H

H

H

H HH

H H

H

H

H

H

H

HH

HH

H

H H

HH

H

Double Bonds are Shown

Depictions of trans 2-pentene

C C

H

CC

H H

H

HH

C

H

HH

H

Lewis Structure

C

CH3

H

C

H

CH2CH3

condensed structural formula

line-angle or zig-zag structure

For Cyclic Structures, Draw the Corresponding Polygon

Cyclohexane

CC

CC

C

C

HHH

HH

HHH

H

HH

H

Some Steroids

HOCholesterol

C27H44O

OH

OTestosterone

C19H26O2

Adrogenic/Anabolic Steroids

CH3

O

CH3OH

H

H

H

Testosterone

CH3

O

CH3

H

H

H

O

Androstenedione

Anabolic Steroids

O

CH3OH

H

H

H

CH3

CH3

H

H

HN

N

CH3

OH

H

Nandralone Stanozolol

Benzene can be drawn as one of two resonance structures

CC

CC

C

C

H

H

H

H

H

H

CC

CC

C

C

H

H

H

H

H

H

Some Line-Angle Structures