Lecture 21

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Review of Organic Chemistry: Structures and Reactions of Organic Molecules

Reading Assignment: Read the information boxes on orgainc molecules at the Okanagan University College web site listed elow. Read the slide presentations on Professor James Hardy's web site, University of Akron, and click on the examples for (1) alkanes, (2) unsaturated hydrocarbons, (3) alcohols, phenols and ethers, (4) aldehydes and ketones, (5) carboxylic acids, and (6) amines and esters. Read Manahan, Chapter 23--Toxicological Chemistry. Download the chime plug-in and study the different molecules on the molecular models web site linked below.

Homework: HW-7 Due Thursday, March 8.

Links and Additional Resources:

Molecular Models at the Okanagan University College Web site


General Organic Chemistry Web site at the University of Akron

NOTE: The 3-D structures included in this lecture require a plug-in for your browser called Chime. It is available free from the MDL Web site MDLChime Plug-in. Although Chime is configured to work with IE and Netscape, we recommend using Netscape 4.80 with Chime 2.60 for optimum results.


A very large percentage of the substances that cause detrimental effects on the environment are synthetic organic molecules. These substances have been shown to accumulate in the food chain and to degrade very slowly in the environment. It is necessa ry to have a general understanding of the properties of these molecules before we can understand their behavior in the environment, and before actions can be take to remove them from areas that have been contaminated with organic chemicals.

Organic Chemistry:

  1. Organic molecules are substances where carbon is the basic structural component of the molecule.
  2. Two properties affect the behavior of organic molecules in the environment: physical properties and chemical properties.

Physical Properties:

  1. Solubility in water
  2. Solubility in fatty tissue
  3. Volatility

Chemical Properties:

  1. Reactivity (Degradability)

Physical Properties (General Rules for Organic Molecules):

  1. Molecules that contain only carbon, hydrogen and chlorine are not soluble in water.
  2. Molecules that contain only carbon, hydrogen and chlorine are "fat" soluble.
  3. Molecules that contain only carbon, hydrogen and chlorine are volatile.
  4. Organic molecules that contain oxygen are soluble in water than the corresponding hydrocarbon.
  5. Organic molecules that contain oxygen are less volatile than the corresponding hydrocarbon.

Chemical Properties (General Rules for Organic Molecules):

  1. Saturated molecules that contain only carbon, hydrogen and chlorine are non-reactive.
  2. Branched hydrocarbons are less reactive than "straight chain" hydrocarbons.
  3. Hydrocarbons that contain a double bond are more reactive than the corresponding saturated hydrocarbon.
  4. Hydrocarbons that contain a triple bond are more reactive than the corresponding hydrocarbon with a double bond.
  5. Hydrocarbons that contain oxygen are more reactive than the corresponding hydrocarbon.

Lewis Representations for Atoms

  1. Each valence electron is represented by a dot next to the symbol for the element.
  2. Hydrogen can have a maximum of two electrons in its valence shell
  3. The other first row elements can have a maximum of eight electrons in their valence shells.
Hydrogen Carbon Oxygen

Nitrogen

Chlorine

Combining Atoms to Form Molecules:

3-D structure of methane

Lewis Rules for Molecules:

  1. A covalent bond is represented by two electrons shared between the atoms.
  2. Atoms will assume an electron configuration such that there are eight electrons (an octet) around each atom.
  3. Hydrogen has two electrons in its valence shell.
  4. Atoms can share two, four or six electrons, which would be described as single, double and triple bonds.
  5. Each electron pair is represented by a single, straight line.

The Lewis Rules help us understand the bonding in organic molecules, and help to keep track of the electrons.

The Lewis Rules do not tell us anything about the shape or structure of molecules.

There are three kinds of carbon atoms:

  1. Single bonded carbon atoms that form four single bonds to other atoms. These atoms are tetrahedral with four bonds, separated by 109 .
  2. Double bonded carbon atoms that form two single bonds and one double bond (four total bonds) to other atoms. These atoms are planar (flat) with an angle of 120 between the bonds.
  3. Triple bonded carbon atoms that form one single bond and one triple bond (four total bonds) to other atoms. These atoms are linear with an angle of 180 between the bonds.

The structure of organic molecules is very important, because many of the physiological properties of these substances are based on the shape and size of the molecule.

Ways to represent ethane (C2H6):

3-D structure of ethane

Ways to represent ethene, or ethylene (C2H4):

3-D structure of ethylene

Ways to represent ethyne, or acetylene (C2H2):

3-D structure of acetylene

Inserting an oxygen atom between the carbon and hydrogen atoms leads to a new class of organic molecules called alcohols. The two-carbon alcohol is called ethyl alcohol or ethanol.

3-D structure of ethanol

An oxygen atom that has a double bond with carbon will be in one of three classes of organic compounds. An aldehyde results from a carbon atom forming a double bond to oxygen, and a single bond to carbon and a single bond to hydrogen. Acetaldehyde is an example:

3-D structure of acetaldehyde

A ketone results from a carbon atom forming a double bond to oxygen, and both single bonds are to other carbon atoms. Acetone is an example:

3-D structure of acetone

A carboxylic acid results from a carbon atom forming a double bond to oxygen, and one single bond is to a carbon atom and the remaining single bond is to a hydroxyl group (-OH). These compounds are called carboxylic acids. Acetic acid is an example:

3-D structure of acetic acid

An important class of organic molecules in photochemical smog formation is the peroxyacids. These result when a carbon atom forms a double bond to oxygen, one single bond is to a carbon atom and the remaining single bond is to a peroxide group (-OOH). An example is peracetic acid:


ENV 440 - Course Topics

Environmental Chemistry -- ENV 440
Last Updated:  03/01/2007