How to ask and answer nomenclature questions?

Question

A small but significant fraction of the questions consists of nomenclature questions.
In principle, virtually all nomenclature questions resemble one another, but they are quite different from other chemistry questions. Therefore, we gathered some guidelines about best practices for asking and answering nomenclature questions.

These guidelines are meant to be recommendations, not absolute rules. The verbal forms “should” and “should not” are used to indicate that among several possibilities one is recommended as particularly suitable, without mentioning or excluding others, or that a certain course of action is preferred, but not necessarily required, or that (in the negative form) a certain possibility or course of action is deprecated but not prohibited.
This specifically excludes changing a question after it was answered. Chameleon questions will be rolled back to the last edit, where the answer still made sense.

The recommendations for questions and answers belong together, since usually the best way to answer depends on the actual question and the best way to ask a question depends on the expected answer. We decided to give an overview first, while extending the specific points in separate answers.

You may discuss the recommendations in comments below each post. These guidelines have been established through general agreement based on the SE voting system. If you think something is missing or there is a mistake you can edit the post itself. However, it might be a better course of action to discuss drastic changes first.
If you would like to propose an alternative strategy, or your comment is too long, you can add another answer for discussion, which may later be incorporated into the existing ones.

Note that virtually all nomenclature questions ask for the name for a given chemical structure (convert structure to name). Although the opposite direction (convert name to structure) may occur in nomenclature questions; the present recommendations are focused on the most frequent case.

Answer 1

Asking nomenclature questions

• Many nomenclature questions may be considered homework-like questions, even if they are not actual homework assignments. (For more details see the homework policy.)

• For most compounds, a thorough derivation of the complete name would involve many nomenclature rules, and therefore would be too long for this format.

• The correct answer to your question may depend on the particular case, and thus it may not be generally applicable to all cases.

• Complicated chemical structures depend on structural representations exhibiting the atom–atom connectivity, the order of the bonds, and the stereochemistry.

• Any edits to the question must not invalidate answers that have already been given. Changes that invalidate answers will be rolled back.

• The title of the question shall be as descriptive as possible.

• Tags are a means of finding experts who are able to answer by sorting questions into specific, well-defined categories.

See below for a more detailed explanation of asking nomenclature questions.

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Answering nomenclature questions

• Since many compounds can have two or more names in accordance with several methods recommended by IUPAC, a compound may be named correctly in more ways than one.

• The rules for systematic nomenclature have changed several times. Furthermore, various drafts, corrections, extensions, modifications, and revisions have been issued.

• We are looking for long answers that provide some explanation and context.

• Names are written in accordance with a symbolism specific to the nomenclature in order to avoid ambiguity and to establish an unequivocal relationship between a name and the corresponding structure.

See below for a more detailed explanation of answering nomenclature questions.

Answer 2

Asking nomenclature questions

Many nomenclature questions may be considered homework-like questions, even if they are not actual homework assignments.

If applicable, you should follow the homework policy.

In particular, do not just copy the exact problem from your homework assignment or textbook.

You should show your work and explain what you have been able to figure out so far and how you did it.

You should narrow down the problem to the particular concept that is giving you trouble and ask about that specifically (see next item).

For most compounds, a thorough derivation of the complete name would involve many nomenclature rules, and therefore would be too long for this format.

You should add details to narrow the answer set or to isolate an issue that can be answered in a few paragraphs. Ideally, try to limit your question to a single nomenclature rule.

You should ask only one question per post; therefore, you usually should ask about only one compound per post. Generally, you should not ask about the complete names of several different compounds in one question, even if the involved issues seem to be similar.

However, you may ask about the differences between names of similar structures.

You should not include other questions about properties of the concerned compound that are not related to nomenclature; e.g. you should not ask “What is the name of this compound and why does it not react with bromine?”

The correct answer to your question may depend on the particular case, and thus it may not be generally applicable to all cases.

You should include one (and preferably only one) exact example structure that illustrates your problem. Ideally, the example structure should be complete and should neither include generic placeholders nor undefined substituents (e.g. neither $\ce{-R}$ nor $\ce{-X}$).

Complicated chemical structures depend on structural representations exhibiting the atom–atom connectivity, the order of the bonds, and the stereochemistry.

Simple chemical structures can often be represented by a line formula*, such as $\ce{C6H5COOH}$, but for complicated chemical structures, you should include an image that shows a chemical structure diagram of the whole molecule.

The chemical structure diagram does not have to be perfect, but it should clearly and unambiguously represent the atom–atom connectivity, the order of the bonds, and (if relevant) the stereochemistry.

If you need further guidance on how to draw chemical structure diagrams, you might want to consider reading Graphical Representation Standards for Chemical Structure Diagrams (IUPAC Recommendations 2008) and Graphical Representation of Stereochemical Configuration (IUPAC Recommendations 2006). However, when asking a nomenclature question, you do not have to follow all recommendations in these publications.

Any edits to the question must not invalidate answers that have already been given.

You may always edit the text of your question; however, you must not change or expand the actual question after it has received one or more answers. Changes to the question, that invalidate answers will be rolled back.

If you want to extend your question, please ask a new one by clicking the Ask Question button. Include a link to your previous question if it helps provide context.

To request clarification from an author, leave a comment below their post. Note that you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post (currently 50 points).

The title of the question shall be as descriptive as possible.

Generally, the wording of the title shall be established with great care; while being as concise as possible, it shall indicate, without ambiguity, the subject matter of the question in such a way as to distinguish it from that of other questions, without going into unnecessary detail.

However, it is in the nature of nomenclature questions that it is difficult to find a precise title for a question if you do not know the name of the concerned compound.

Nevertheless, you should not use vague generic titles, such as “What is the name of this compound?” You should give more precise details and describe the particular issue that is giving you trouble, e.g. “What is the systematic name of this cyclic ester derived by multiple esterification?”

Tags are a means of finding experts who are able to answer by sorting questions into specific, well-defined categories.

Generally, you should add the nomenclature tag.

You should choose additional tags that best describe your question.

Usually, you should add either the inorganic-chemistry tag or the organic-chemistry tag.

If your question involves the naming of stereoisomers, you should add the stereochemistry tag.

Furthermore, several tags for functional groups are available.

*Note
According to IUPAC recommendations concerning nomenclature of organic as well as inorganic chemistry, a line formula is a formula that is written on a single line, as is text. Unfortunately, however, there are also other definitions of line formula.

Answer 3

Answering nomenclature questions

Since many compounds can have two or more names in accordance with several methods recommended by IUPAC, a compound may be named correctly in more ways than one.

Generally, you should include the preferred IUPAC name (PIN), which is the name preferred among two or more names generated from two or more IUPAC recommendations including retained names. In addition, you may include other systematic names or retained names that are acceptable in general nomenclature.

If known, you should state whether the name is the PIN or just one of the other correct names.

If not obvious, you should also mention whether the name is a systematic name or a retained name.

Any names used in the past, but now discarded or no longer recommended, should be marked as such.

The rules for systematic nomenclature have changed several times. Furthermore, various drafts, corrections, extensions, modifications, and revisions have been issued.

Therefore, you should state which edition (year of publication) of the IUPAC nomenclature you have used.

Preferably, you should use the current official edition including the latest corrections.

We are looking for long answers that provide some explanation and context.

Do not just give a one-line answer; explain why your answer is right.

You should not rely on automatic algorithms to generate the PIN. A number of chemical structure drawing programs are available to generate names for chemical structures; however, all known programs have limitations or shortcomings. In particular, the algorithms may not include all rules or they may use obsolete rules.

You should add citations to reliable sources that support the answer, ideally to original IUPAC publications. Note that, without further references, Wikipedia is not considered a reliable source. You should also not rely on chemical catalogues (e.g. Sigma-Aldrich) or online databases (e.g. ChemSpider or PubChem).

If possible, you should provide a link to the original page or publication.

Do not give a link-only answer. While the link may answer the question, it is better to include the essential parts into your answer and provide the link for reference. Note that link-only answers can become invalid if the linked page changes.

You should quote the relevant portion of the nomenclature rules.

P-65.1.2.1 Carboxylic acid groups, $\ce{-COOH}$, that conceptually replace a $\ce{-CH3}$ group of methane or terminate an unbranched hydrocarbon chain are named by replacing the final ‘e’ of the name of the corresponding hydrocarbon by the suffix ‘oic acid’. (…)

If not clear from the context, you should mention whether the quoted rule is an official IUPAC rule or a simplified or paraphrased rule from other sources.

Note that answers that do not include explanations and sources may be disputed or deleted.

Do not try to answer in comments. Answers in comments – especially wrong ones, including links to sources of wrong information – may be deleted immediately.

Names are written in accordance with a symbolism specific to the nomenclature in order to avoid ambiguity and to establish an unequivocal relationship between a name and the corresponding structure.

All names should be written in accordance with the recommended symbolism. This includes

• spelling,
• elision or addition of vowels,
• capitalized and uncapitalized letters and words,
• spaces,
• punctuation (e.g. commas, full stops, colons, semicolons, hyphens, ‘em’ dashes, plus and minus signs, dots, solidi, primes),
• enclosing marks (parentheses, square brackets, and braces),
• italics, and
• Greek letters.

Note that the recommended symbolism is particularly important in the formation of PINs.

It may be useful to include an image that shows a chemical structure diagram of the named compound.

Including an image in the answer may be useful in order to avoid misunderstanding, for example if the description or image in the question is unclear or changed later. The image should make it clear to which compound the answer is referring to.

Including an image in the answer may be useful for readers because they do not have to scroll back to the question when they want to see the structure diagram of the concerned compound.

The structure diagram should be correct, i.e. in accordance with customary graphical representation standards or style guides. If you need further guidance on how to draw chemical structure diagrams, you might want to consider reading Graphical Representation Standards for Chemical Structure Diagrams (IUPAC Recommendations 2008) and Graphical Representation of Stereochemical Configuration (IUPAC Recommendations 2006). However, the context of the answer may favour a different representation, so that, for example, substituents may be treated alike or the construction of the name may be recognized. If desired, the structure diagram may show atom numbers or stereodescriptors.