NOMENCLATURE: GENERAL CONSIDERATIONS
(>>PROBLEMS)

You are responsible for all the material contained in this handout, including the identities and prioritization of the functional groups (click here).

You may be asked to draw a structure from common nomenclature, but if asked to generate a name for any given structure, always use IUPAC.

This worksheet starts from the premise that you have a basic knowledge of nomenclature, including:

- Identifying the longest chain
- Parent alkane nomenclature (e.g., ethane, nonane, dodecane, etc.)
- Naming and numbering of substituents, including compound substituents
   (e.g., 1,1-dimethylethyl)
- Proper use of parentheses and brackets for substituents
- Use of di-, tri-, tetra-, and bis-, tris-, and tetrakis- conventions
- Proper ordering of the substituents in the written name (e.g., alphabetization)

If this is rusty, please review in the textbook. Your CD-ROM is also an excellent tool for this basic brush-up. The following worksheet is designed to hone your skills for the more complex nomenclature that will be encountered on the final.

ACYCLIC COMPOUNDS

Identify the longest chain containing the highest priority functional group. If the compound has double bonds, include as many double bonds as possible in the main chain. Then modify any remaining substituents with the appropriate prefixes. For example:

CARBOCYCLIC COMPOUNDS

If the carbocycle represents the longest chain, then it becomes the parent compound. If the carbocycle is connected to a chain which is longer, then the carbocycle modifies that chain. Also, if a shorter chain contains a high priority functional group, it takes precedent. For example:

BICYCLIC COMPOUNDS

For fused and bridged bicyclic compounds, there are always two carbons which are part of both rings. The parent alkane is considered to contain all the carbon atoms in both rings. The parent name is then preceded by bicyclo[l.m.n]-, where l, m, and n represent the number of carbons between the two shared carbons. For example (arrows indicate the shared carbons):

Numbering on bicyclic species simply begins at one shared carbon atom, then goes around the largest ring first, in such a way that gives the lowest number to any functionality on the ring. For example:

AROMATIC RINGS AND HETEROCYCLES

You should be familiar with the following aromatic rings and heterocycles (IUPAC names in bold):

These structures are treated as parent compounds when connected to simple substituents (e.g., methylbenzene, methylcyclopropane), but are named as modifiers when high-priority functionality is contained on another chain. For example:

You should also be aware of special cases when these substituents are connected directly to an acid functionality:

RELATIVE AND ABSOLUTE STEREOCHEMISTRY

It is often desirable to indicate relative stereochemistry only, without designating absolute configurations. For example:

Note that in each case we have said nothing about absolute stereochemistry, even though there are two chiral centers in the molecule. We wish only to designate the orientation of the substituents relative to each other (thus, relative stereochemistry).

Recognize, however, that each relative configuration can embrace two enantiomers. For example:

Note that when you specify the absolute stereochemistry on both chiral centers, there is no need to use the cis/trans convention.

In the case of alkenes, relative stereochemistry is specified as cis/trans when the the alkenes are disubstituted, and E/Z when the alkenes are tri- or tetrasubstituted. For example,

Note that in the latter case, E/Z is used for designating both double bonds-this is considered more elegant. Indeed, the middle example could have just as easily been named (Z)-4-hexen-2-one. Also note that the nitrile carbon counts as a member of the parent chain (i.e., the 1-position). This is also true for carboxylic acids.

RESOURCES

There is a very good tutorial on the basics at a website maintained by Dave Woodcock at Okanagan University College (click here). The official IUPAC rules are also available on the web (click here).

I have also constructed a guided tutorial in the form of twelve problems. The tutorial walks you through the methodology of how I think it best to approach nomenclature in general. You will get more out of this exercise if you really try to work through each step, rather than simply clicking through the presentation. To access the problems click here.

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