Carbon-based Compounds and Functional Groups
Hydrocarbons and Alkanes:
As previously mentioned, because carbon has four valence electrons and makes covalent bonds, it can form molecules that are long chains. There are several different kinds of these we will be discussing: hydrocarbons, carbohydrates, lipids, proteins, and DNA. Because of the many important and unique properties of carbon-based molecules, there is a special branch of chemistry devoted just to the study of these molecules. Organic chemistry is the study of compounds containing carbon.
Some Alkanes Hydrocarbons are molecules consisting of/containing only atoms of carbon and hydrogen. There are many different kinds of hydrocarbons based on different numbers of carbon atoms in the molecules and whether or not any of the carbons are connected by double bonds rather than single bonds. In double bonds, two pairs (a total of four) electrons are shared between the two atoms involved. Since carbon has four valence electons, it can make four single bonds with other atoms by sharing one of its electons and one of the other atoms’ electons with each of those atoms. In a double bond, carbon would share two of its electrons and two electrons from another atom with that atom (= two pairs of electrons). This would mean that this carbon atom would, then, have only two other electrons available for bonding with any other atoms. For example, if a carbon is single bonded to another carbon, it could also be bonded to three hydrogens, but if a carbon is double bonded to another carbon, then it can only bond to two hydrogens. Note that in the word “hydrocarbon” the “hydro” part refers to hydrogen, not to water: there is no water in hydrocarbons, only hydrogen and carbon. Generally, hydrocarbons are not found in living organisms, but are found in quantity in fossil fuels, which used to be living organisms. Because their structures are the simplest to understand and because they form the building-blocks from which other organic molecules are made, we will look first at the structures of hydrocarbons.
Here are the names of the first ten hydrocarbons with all single bonds. These have the general formula: CnH2n+2, where any number could be substituted for the “n.” Note that all these names end in “-ane,” which is an ending that signifies a hydrocarbon with all single bonds).
|1||methane||methyl = wine|
|2||ethane||ether = upper air|
|3||propane||pro = before, in front of|
|4||butane||butyr = butter|
|5||pentane||penta = 5|
|6||hexane||hexa = 6|
|7||heptane||hepta = 7|
|8||octane||octa = 8|
|9||nonane||nona = 9|
|10||decane||deca = 10|
Click on the name of a functional group, then click on the group in this picture.
Alcohol (Hydroxyl Group)
Aldehyde (Carbonyl Group)
Ketone (Carbonyl Group)
Carboxylic Acid (Carboxyl Group)
Amine (Amino Group)
Amino Acid (Amino Group + Carboxyl Group)
As just mentioned, generally “plain” hydrocarbons are not found in in living cells. There are usually other groups of atoms attached somewhere on the molecule. There are certain groups of atoms that are frequently attached to the organic molecules we will be studying, and these are called functional groups. These are things like hydroxyl groups which form alcohols, carbonyl groups which form aldehydes or ketones, carboxyl groups which form carboxylic acids, and amino groups which form amines. These groups tend to act the same and have similar properties no matter where on a carbon backbone molecule they’re stuck. Additionally, a molecule may have more than one functional group and/or more than one type of functional group attached. For example, later, we will be discussing glycerol, which is a propane with a hydroxyl group in place of one of the hydrogens on each of the three carbons. Another example would be amino acids, which have both both an amino group and a carboxyl group attached. We will be discussing each of these functional groups in more detail as we discuss the various types of molecules that contain them.
Two Important Reactions:
As we look at the various types of molecules and how they are formed, we will see two special reactions again and again in a number of situations. These two reactions are exact opposites. Dehydration Synthesis involves taking water (one O and two H) out from two smaller molecules to cause them to bond together to make one larger molecule. Hydrolysis involves adding water into a specific place in one large molecule to cause it to break into two smaller ones.
Click on either of
these pictures to animate it.
|>>> Dehydration Synthesis <<<||<<< Hydrolysis >>>|
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Campbell, Neil A., Lawrence G. Mitchell, Jane B. Reece. 1999. Biology, 5th Ed. Benjamin/Cummings Publ. Co., Inc. Menlo Park, CA. (plus earlier editions)
Campbell, Neil A., Lawrence G. Mitchell, Jane B. Reece. 1999. Biology: Concepts and Connections, 3rd Ed. Benjamin/Cummings Publ. Co., Inc. Menlo Park, CA. (plus earlier editions)
Marchuk, William N. 1992. A Life Science Lexicon. Wm. C. Brown Publishers, Dubuque, IA.
Sienko, Michell J. and Robert A. Plane. 1966. Chemistry: Principles and Properties. McGraw-Hill Book Co., NY. (and other chemistry texts and handbooks)Copyright © 1996 by J. Stein Carter. All rights reserved.