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| Nomenclature of Carbohydrates
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| Carbohydrates are a broad group of organic compounds. As the name implies, they are hydrates of carbon. That is, they consist of carbon, hydrogen and oxygen. These elements can be joined in a broad variety of ways. Some of the more common carbohydrates are alcohols, aldehydes, ketones, ethers, organic acids, esters and saccharides.
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| Alcohols have one or more hydroxyl groups (-OH) joined to a hydrocarbon. The presence of a hydroxyl group is denoted by adding "-ol" as a suffix. If there are more than two carbon atoms in the molecule, a numerical prefix identifies the position of the hydroxyl group. Methanol (CH3OH), also known as wood alcohol, is poisonous. Ethanol (C2H5OH) is drinking alcohol. Alcoholic beverages have varying contents of ethanol in a mixture of alcohol and water, plus possible flavorings. Beer is 4-8% ethanol, wine is 16-24% ethanol, gin, rum and whiskey are 36-50% ethanol and vodka is 40-95% ethanol. 2-propanol, also known as isopropanol or rubbing alcohol (CH3CHOHCH3), has the hydroxyl group joined to the middle carbon atom in a three-carbon chain.
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| Aldehydes and ketones have an oxygen atom joined to a carbon atom with a double bond called a carbonyl group. If it is joined to a terminal carbon atom, the compound is an aldehyde. The compound has the ending of "-al" or, in the older terminology, it would be a prefix denoting the carbon chain, followed by "aldehyde." Thus, CH2O is methanal or either methyl aldehyde or formaldehyde. It would be easier if only one term was used, but any are possible, depending on the literature or label being read. C2H5O is ethanal or either ethyl aldehyde or acetaldehyde. Similarly, C3H8O is propanal or propionaldehyde. If the double bonded oxygen is joined to a central carbon atom, it is identified as a ketone. The proper ending is then "-one." Propanone is an isomer of propanal. An alternate common name is acetone. If there are more than three carbon atoms in the chain, a prefix identifies where the carbonyl group is positioned, counting from the closest end of the chain. Aldehydes and ketones are widely used in pharmaceutical, food, fragrance and cosmetics industries
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| Ethers have an oxygen atom connecting two hydrocarbon branches. The older nomenclature requires naming the two branches in alphabetical order, followed by the "ester" as the end of the name. If both branches are the same, the prefix "di" is used. The IUPAC name has a prefix of the shorter branch followed by "oxy" and concluded by the name of the longer branch. By these rules, CH3OCH3 is either dimethyl ether or methoxymethane. Similarly, CH3OC2H5 is either ethyl methyl ether or methoxyethane. Ethers are primarily used as solvents.
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| If a hydroxyl group is joined to a carbonyl group, it forms a carboxyl group (-COOH), which identifies an organic acid. The name for the compound has a prefix identifying the hydrocarbon with the ending of "-oic acid." (The older names had the ending of "-ic acid," which is sometimes used in common grammar. The simplest organic acid, having only one carbon atom, is methanoic acid, formerly known as formic acid. The formula is HCOOH. This compound is produced by various ants and beets and stinging nettle, accounting for the burning sensation of bites or stinging. Ethanois acid, also known as acetic acid, has two carbon atoms. The formula is CH3COOH. If two carboxyl groups are joined together, it produces ethanedioic acid, commonly known as oxalic acid. The formula for oxalic acid is (COOH)2. The range of organic acids is extensive.
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| In neutralization, an acid reacts with a base to produce a salt and water. For example, in producing table salt (sodium chloride), HCl + NaOH --> NaCl + H2O. An equivalent reaction in organic chemistry is esterification. An organic acid reacts with an alcohol to yield an ester and water. The functional group of an ester is -COO-. The hydrogen ion of the organic acid has been replaced by the component from the alcohol. The name for an ester ends with "-ate." If ethanol reacts with acetic acid, the product is ethyl acetate, formally known as ethyl ethanoate. The formula is CH3COOCH2CH3. Methanol reacts with salicylic acid to produced methyl salicylate, commonly known as "oil of wintergreen," which is the active component in Bengay. Our nose has a favorable response to many esters, so they are used in fragrances and cosmetics.
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| Saccharides, commonly known as sugars, are carbohydrates that generally have a 2:1 ration of hydrogen to oxygen, matching the ratio in water. Glucose (blood sugar), fructose (fruit sugar) and galactose are monosaccharides. They all have the formula of C6H12O6 and are isomers of one another, though our tongue responds differently to each. If two monosaccharides are joined together, releasing a water molecule, the product is a disaccharide. Examples are sucrose (table sugar), maltose (malt sugar) and lactose (milk sugar). They have the formula of C12H22O11. People who are unable to decompose lactose are said to be lactose intolerant. Molecules made from a long chain of monosaccharides, such as starch and cellulose, are polysaccharides.
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