Carbon and Intermolecular Forces Essay

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Organic Chemistry, Fourth Edition
Janice Gorzynski Smith
University of Hawai’i

Chapter 3
Lecture Outline
Prepared by Layne A. Morsch
The University of Illinois - Springfield

Copyright © 2014 The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

1

Functional Groups
• A functional group is an atom or a group of atoms with characteristic chemical and physical properties.
• Most organic molecules contain a carbon backbone consisting of C-C and C-H bonds to which functional groups are attached.
• Structural features of a functional group include:
• Heteroatoms—atoms other than carbon or hydrogen. • π Bonds most commonly occur in C-C and C-O double bonds.
2

Functional Groups
• Functional groups distinguish one organic molecule from another. • They determine a molecule’s:
• geometry
• physical properties
• reactivity

3

Reactivity of Functional Groups
• Heteroatoms and π bonds confer reactivity on a particular molecule. • Heteroatoms have lone pairs and create electrondeficient sites on carbon.
• A π bond makes a molecule a base and a nucleophile, and is easily broken in chemical reactions.

4

Hydrocarbons
• Hydrocarbons are compounds made up of only the elements carbon and hydrogen.
• They may be aliphatic (ex. alkanes, alkenes, alkynes) or aromatic.

5

Aliphatic Hydrocarbons
• Aliphatic hydrocarbons have three subgroups.
• Alkanes have only C—C σ bonds and no functional group. • Alkenes have a C—C double bond.
• Alkynes have a C—C triple bond.

6

Aromatic Hydrocarbons
• Aromatic hydrocarbons are so named because many of the earliest known aromatic compounds had strong, characteristic odors.
• The simplest aromatic hydrocarbon is benzene.
• The six-membered ring and three π bonds of benzene comprise a single functional group, found in most aromatic compounds.

7

Functional Groups with CarbonHeteroatom (C-Z) σ bonds
• Several types of functional groups contain C-Z σ bonds. • The electronegative heteroatom Z creates a polar bond, making carbon electron deficient.

8

Functional Groups with C-Z σ bonds

9

Functional Groups with C=O Group
• This group is called a “carbonyl group”.
• The polar C-O bond makes the carbonyl carbon an electrophile, while the lone pairs on O allow it to react as a nucleophile and base.
• The carbonyl group also contains a π bond that is more easily broken than a C-O σ bond.

10

11

Importance of Functional Groups
A functional group determines all of the following properties of a molecule:
• bonding and shape
•

type and strength of intermolecular forces • physical properties
• nomenclature
• chemical reactivity
12

Molecules can Contain Several
Functional Groups

• Each of these molecules have several different functional groups
• These molecules would also have several different types of reactivity
13

Question
• Identify the functional groups in the molecules shown.

14

Intermolecular Forces
• Intermolecular forces are interactions that exist between molecules. • Functional groups determine the type and strength of these interactions.
• Ionic and covalent compounds have very different intermolecular interactions.

15

Ion-Ion Interactions
• Ionic compounds contain oppositely charged particles held together by extremely strong electrostatic interactions. • These ionic interactions are much stronger than the intermolecular forces present between covalent molecules. 16

Intermolecular Forces in Covalent Molecules
• Covalent compounds are composed of discrete molecules. • The nature of the forces between molecules depends on the functional group(s) present.
• There are three different types of interactions, shown below in order of increasing strength:
§ van der Waals forces
§ dipole-dipole interactions
§ hydrogen bonding

17

van der Waals Forces
• van der Waals forces are also known as London forces.
• They are very weak interactions caused by momentary changes in electron density in a molecule.
• They
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