Thank you for taking Chem108: Organic and Biochemistry.
1
Chapter 11
Introduction to Organic Chemistry
2
Organic Chemistry: The Chemistry of Carbon Compounds.
•
•
•
•
•
•
The element carbon has a special role in chemistry because it
bonds with other carbon atoms to give a vast array of molecules.
The variety of molecules is so great that we find organic
compounds in many common products such as gasoline,
medicine, shampoos, plastic bottles, perfumes, etc.
The food we eat is also composed of different organic
compounds that supply us with fuel for energy and the carbon
atoms needed to build and repair the cells of our bodies.
Large organic molecules make up the proteins in hair and skin,
the lipids in cell membranes and adipose
Although many organic compounds occur in nature, chemists
have synthesized even more. The cotton, wool, or silk in your
clothes contain naturally occurring organic compounds, whereas
materials such as polyester, nylon, or plastic have been
synthesized through organic reactions.
Sometimes, it is convenient to synthesize a molecule in the lab
even though that molecule is also found in nature. Example:
Vitamin C.
3
Study Goals
1. Identify the number of bonds for carbon and other
atoms in organic compounds.
2. Describe the tetrahedral shape of carbon with single
bonds in organic compounds.
3. Classify organic compounds as polar or nonpolar.
4. Describe the properties that are characteristic of
organic compounds.
5. Identify the functional groups in organic compounds.
6. Write condensed structural formulas for organic
compounds.
7. Write structural formulas for constitutional isomers.
4
11.1 Organic Compounds
Review: Bonding:
• Ionic Bonding—transfer of electrons.
So:
5
Bonding (continued):
• Covalent Bonding—sharing of electrons.
H + H
H ..H
Each H shares
two electrons.
The simplest way to symbolize the bonding
of a covalent molecule is to use Lewis dot
structures. In doing so, it is important to
remember the octet rule.
6
Octet Rule:
• Atoms will react (i.e. gain, lose or share
electrons) in order to have the same number
of valence electrons as the nearest noble
gas. The sum of all the shared and unshared
valence electrons about an atom must total
8. Note that this does not apply to all atoms
(e.g. H, B, and sometimes Al, S.)
7
Lewis/Kekule Structures
• dots = electrons
• line = two shared electrons
• all unshared electrons are shown, and are
referred to as nonbonding electrons. Each
pair of non-bonding electrons is also known
as a “lone pair”
H
H
CH3Cl
H C Cl
H
Lewis
H
C
Cl
H
Kekule
8
Multiple bonding in Lewis/Kekule
structures:
• Single Bond: sharing of one electron pair
between two atoms.
• Double Bond: sharing of two electron pairs.
• Triple Bond: sharing of three electron pairs.
9
10
Sample Problem: Complete the following structures by
adding the correct number of hydrogen atoms:
a. C—C—C—N—C—C—N
b. O—C—C—O—C—C—Cl
Solution
H H
H H
H H
H
a. H—C—C—C—N—C—C—N—H
H H
H
H H
H
H
H H
b. H—O—C—C—O—C—C—Cl
H
H
H H
11
Question
How many bonds will oxygen make?
a.
b.
c.
d.
1
2
3
4
Answer: “b”.
12
Question
How many bonds will nitrogen make?
a.
b.
c.
d.
1
2
3
4
Answer: “c”.
13
Question
The atoms in the compound below are numbered 1-4. How many hydrogens are
needed on each atom to complete the structure?
a Atom 1 needs 3 hydrogens; atom 2 needs 3 hydrogens; atom 3 needs
. 1 hydrogen; atom 4 needs 3 hydrogens.
b Atom 1 needs 2 hydrogens; atom 2 needs 2 hydrogens; atom 3 needs
. 1 hydrogen; atom 4 needs 3 hydrogens.
c Atom 1 needs 3 hydrogens; atom 2 needs 2 hydrogens; atom 3 needs
. 1 hydrogen; atom 4 needs 3 hydrogens.
d Atom 1 needs 3 hydrogens; atom 2 needs 2 hydrogens; atom 3 needs
. 2 hydrogens; atom 4 needs 3 hydrogens.
Answer: “c”.
14
Shells, Subshells and Orbitals
15
The electrons in the electron SHELLS or Main ENERGY LEVELS can
be described in more detail. Within each shell, the electrons with
identical energy are grouped as SUBSHELLS, which are identified by
the letters s, p, d, and f. The s subshell has the lowest energy, followed
by the p subshell, then the d subshell, and finally the highest energy
16
subshell. Page 69, Figure 2.10.
The shapes of orbitals differ; s orbitals are spherical and p
orbitals are dumbbell shaped. Each orbital holds a maximum of
two electrons.
17
The  bond is formed by overlapping of two p orbitals on
adjacent carbon atoms.
18
In ethyne, C2H2, the overlap of two p orbitals forms two 
bonds required for the triple bond.
19
11.2 The Tetrahedral Structure of Carbon
In most organic molecules, a carbon atom is bonded
to four other atoms. The VSEPR (Valence-Shell
Electron-Pair Repulsion) theory predicts that when
four bonds are arranged as far apart as possible,
they have a tetrahedral shape.
VSEPR theory: A theory that predicts the shape of a
molecule by moving the electron pairs on a central
atom as far as possible to minimize the repulsion of
the negative regions.
(Review: what are the shapes of the molecules of
CH4, CO2 and NH3)
20