SAT Subject Test Chemistry
REVIEW OF MAJOR TOPICS
Carbon and Organic Chemistry
Alcohols—Methanol and Ethanol
The simplest alcohols are alkanes that have one or more hydrogen atoms replaced by the hydroxyl group, —OH. This is called its functional group.
Methanol is the simplest alcohol. Its structure is
Alcohol”s functional group is R—OH. A hydroxyl group is attached to an alkyl stem.
PROPERTIES AND USES. Methanol is a colorless, flammable liquid with a boiling point of 65°C. It is miscible with water, is exceedingly poisonous, and can cause blindness if taken internally. It can be used as a fuel, as a solvent, and as a denaturant to make ethyl alcohol, unsuitable for drinking.
Ethanol is the best known and most used alcohol. Its structure is
Its common names are ethyl alcohol and grain alcohol.
PROPERTIES AND USES. Ethanol is a colorless, flammable liquid with a boiling point of 78°C. It is miscible with water and is a good solvent for a wide variety of substances (these solutions are often referred to as “tinctures”). It can be used as an antifreeze because of its low freezing point, -115°C, and for making acetaldehyde and ether. It is presently used in gasoline as an alternative to reduce the use of petroleum.
Isomeric alcohols have similar formulas but different properties because of their dif ferences in structure. If the —OH is attached to an end carbon, the alcohol is called a primary alcohol. If attached to a “middle” carbon, it is called a secondary alcohol. Some examples:
The number in front of the name indicates to which carbon the —OH ion is attached.
Other alcohols with more than one —OH group:
A colorless liquid, high boiling point, low freezing point. Used as permanent antifreeze in automobiles.
Colorless liquid, odorless, viscous, sweet taste. Used to make nitroglycerine, resins for paint, and cellophane.
The functional group of an aldehyde is the formyl group. The general formula is RCHO, where R represents a hydrocarbon radical.
PREPARATION FROM AN ALCOHOL. Aldehydes can be prepared by the oxidation of an alcohol. This can be done by inserting a hot copper wire into the alcohol. A typical reaction is:
The middle structure is an intermediate structure; since two hydroxyl groups do not stay attached to the same carbon, it changes to the aldehyde by a water molecule “breaking away.”
The aldehyde name is derived from the alcohol name by dropping the -ol and adding -al.
Ethanol forms ethanal (acetaldehyde) in the same manner.
The aldehyde functional group is
A formyl group is attached to an alkyl stem.
Organic Acids or Carboxylic Acids
The functional group of an organic acid is the , carboxyl group. The general formula is R—COOH.
PREPARATION FROM AN ALDEHYDE. Organic acids can be prepared by the mild oxidation of an aldehyde. The simplest acid is methanoic acid, which is present in ants, bees, and other insects. A typical reaction is:
Notice that in the IUPAC system the name is derived from the alkane stem by adding -oic.
The carboxyl group is the functional group of an organic acid. It is
Ethanal can be oxidized to ethanoic acid:
Acetic acid, as ethanoic acid is commonly called, is a mild acid that, in the concentrated form, is called glacial acetic acid. Glacial acetic acid is used in many industrial processes, such as making cellulose acetate. Vinegar is a 4% to 8% solution of acetic acid that can be made by fermenting alcohol.
It is possible to have more than one carboxyl group in a carboxylic acid. In the ethane derivative, it would be ethanedioic acid with a structure like this:
Summary of Oxygen Derivatives
Note: R1 indicates a hydrocarbon chain different from R by having one less carbon in the chain.
An actual example using ethane:
When a secondary alcohol is slightly oxidized, it forms a compound having the functional group , and called a ketone. The R1 indicates that this group need not be the same as R. An example is:
Note that the functional group of ketones is
Example in a longer chain:
In the IUPAC method the name of the ketone has the ending -one with a digit indicating the carbon that has the double-bonded oxygen preceding the ending in larger chains, as shown in butan-2-one. Another method of designating a ketone is to name the radicals on either side of the ketone structure and use the word ketone. In the preceding reaction, the product would be dimethyl ketone.
Note that both aldehydes and ketones contain the carbonyl group in their structures. In the aldehydes, it is at the end of the chain, and, in acids, it is the interior of the chain.
The functional group of ethers is R—O—R1
When a primary alcohol, such as ethanol, is dehydrated with sulfuric acid, an ether forms. The functional group is
R—O—R1, in which R1 may be the same hydrocarbon group, as shown in example 1 below, or a different hydrocarbon group, as shown in example 2.
2. Another ether with unlike groups, R—O—R1:
In the IUPAC method, the ether name, as shown in the examples, is made up of two attached alkyl chains to the oxygen. The shorter of the two chains becomes the first part of the name, with the –ane suffix changed to –oxy and the name of the longer alkane chain as the suffix. Examples are ethoxyethane and ethoxypropane.
Diethyl ether is commonly referred to as ether and is used as an anesthetic.
Amines and Amino Acids
The group NH2− is found in the amide ion and the amino group. Under the proper conditions, the amide ion can replace a hydrogen in a hydrocarbon compound. The resulting compound is called an amine. Two examples:
The amide functional group is
In amides, the NH2− group replaces a hydrogen in the carboxyl group. When naming amides, the -ic of the common name or the -oic of the IUPAC name of the parent acid is replaced by -amide. For example:
Amino acids are organic acids that contain one or more amino groups. The simplest uncombined amino acid is glycine, or amino acetic acid, NH2CH2—COOH. More than 20 amino acids are known, about half of which are essential in the human diet because they are needed to make up the body proteins.
Esters can be compared to inorganic salts.
Esters are often compared to inorganic salts because their preparations are similar. To make a salt, you react the appropriate acid and base. To make an ester, you react the appropriate organic acid and alcohol. For example:
Note the functional group
The name is made up of the alkyl substituent of the alcohol and the acid name, in which -ic is replaced with -ate.
The general equation is:
Esters usually have sweet smells and are used in perfumes and flavor extracts.
Note the functional group
The following chart summarizes the organic structures and formulas discussed in this section.