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Chemical Nomenclature

The International Union for Pure and Applied Chemistry (IUPAC) will someday adopt a new system of chemical nomenclature that expands upon the one scientists currently use for naming hydrocarbons. This new system will emphasize reducing chemical compounds into only a few basic literal components, thereby removing the need to introduce new terms for the more complicated chemicals, while simultaneously making the drawing out of structural formulas of said compounds significantly easier and understandable for both novices and experts. This new system can even be fed into computers to have them replicate the said chemicals, and introduces a streamlined methodology that is far more intuitive and flexible than the current version.

See also SMILES - Simplified Molecular Input Line Specification. This is a system that can acommodate arbitrary compounds, including steroids and other complex ring-structured compounds.

The Current Version

The current version of IUPAC has the following rules:

Basic Hydrocarbons

If a hydrocarbon has all single bonds, then ending is -ane, as in methane.

If a hydrocarbon has one or more double bonds, then ending is -ene, as in ethene.

If a hydrocarbon has one or more triple bonds, the ending is -yne, as in ethyne.

If a hydrocarbon with a double bond has more carbon atoms on both sides of the double bond on the same side, then a -cis- must be added. If on the opposite side, then a -trans- must be added.

In the case of an -ene or an -yne ending, the position of the double or triple bonds is presented either between the base and the ending, as in pent-1-ene, or before the base, as in 1-pentene.

The base is the latin prefix denoting the number of carbons and related hydrogens. Therefore, methane has one carbon with its (4) hydrogens, and ethyne has two carbons and their hydrogens. The list is as follows:

  1. Meth-
  2. Eth-
  3. Prop-
  4. But-
  5. Pent-
  6. Hex-
  7. Sept-
  8. Oct-
  9. Non-
  10. Dec-

Those going above this are extremely rare. Higher ones, such as icosa-, do exist, but only for certain numbers (in this case 20).

Branched Hydrocarbons

Consider the case of 1-methylbutanol, in which a methyl group is attached to a butane, forming a compound with five carbon atoms. The base name is the one that is the longest; in this case, the butane. The attached group is the prefix of the name, and its location is specified. Therefore, the 1-methyl shows what and where the attached carbon is. In the case of multiple, the form would be 1,1-methylbutanol or 1,3-methylbutanol, depending on what the compound is. If a compound has two different types of branches in addition to the main branch, then the prefixes come in alphabetical order (ie. eth- before meth-). The numbers in the prefix are always the lowest possible.

Cyclical Hydrocarbons

Cyclic hydrocarbons are given the cyclo- prefix, such as in cyclohexane.

One special class of cyclical hydrocarbon is benzene, which has 6 carbon atoms but only 6 hydrogen atoms due to its 3 resonant double bonds.

For benzenes with anything attached, the name quickly becomes a mess. Benzene with an OH- group attached is called phenol. Two benzenes sharing a bond is called napthalene. Each variation must therefore be learned separately.

Functional Groups

By functional groups, IUPAC refers to the following:

  • Haloalkanes, with chloro-, bromo-, and iodo
  • Carboxylic acid with -ic acid
  • Esters with ester
  • Ethers with ether
  • Alcohols with -ol or -ol alcohol
  • Aldehydes, with al
  • Ketones, with -one
  • Amines, with -amine
  • Amides, with -amide

Each of these must be learned separately.

The current nomenclature only allows for one of these functional groups in a compound, with the exception of the haloalkanes.

Difficulties with the Current Version

There are no rules for a hydrocarbon with one or more of both a double bond and a triple bond.

Easy to be confused, especially when many distinct components are involved.

Cannot name compounds with ions, and cannot name zwitterions.

Benzene compounds have no standard nomenclature and require memorization separately.

Compounds with multiple distinct formula groups have unusual names which require memorization separately.

Cannot handle sub-branches of branches. For example, if C20 had a branch with 5 carbons and that branch in turn had a methyl group attached, this would not be representable.

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