Some Examples With Multiple Functional Groups Source: Table 5.1, Section P-59.1.9 of the 2013 Blue Book (). These groups include the halides (bromo, chloro, fluoro, iodo), ethers (“alkoxy”), azide and nitro functional groups. For nomenclature purposes, they are forever out of the limelight, subservient to the -ane, -ene, or -yne ending of the parent hydrocarbon (or “parent hydride”, as IUPAC calls it). Some functional groups have been deemed unworthy of ever getting their own suffixes. Functional Groups That Are Always Prefixes: Halides, Alkoxides, Azides, Nitro Let’s move along to the other functional groups. So when an alkene and an alkyne are present in the same molecule, the ending will always be “yne”.įor the purposes of numbering, if there is a tie between an alkene and an alkyne for determining the lowest locant, the alkene takes priority. It depends on what you mean by “priority”.įor the purposes of the name, “-ene” comes before “-yne” alphabetically. When an alkene and an alkyne are present in a molecule, which takes priority? This brings us to a common source of confusion in nomenclature. In the absence of one of the above functional groups, the suffix will always be “-ane”, “-ene”, or “-yne”, depending on whether any unsaturation is present in the molecule, and any lower-ranked substituents will be prefixes. If no higher-priority groups are present, the suffix for a molecule containing an alkene will be “-ene”, such as in pent-1-ene.įor an alkyne, the corresponding prefix is “-yn” and the suffix is “yne”.Īt this point the methodology for naming molecules changes slightly. The presence of the double bond is noted with the locant followed by the prefix, “en-“. So for a molecule with an alkene and an alcohol, the alcohol has priority and the molecule has the suffix, “-ol”. If carbon-carbon multiple bonds are present in the molecule, they are considered as substituents with a priority (or “seniority”, according to IUPAC) lower than that of amines. Next In Line: Nitrile, Aldehyde, Ketone, Alcohol, Thiol, AmineĪgain, this is not a complete list – we’re cherry picking the most commonly encountered functional groups here. The “seniority rules” continue in the following order, where we are cherry-picking the most common examples. IUPAC goes into way more detail than we need to here. Note that with the exception of sulfonic acids, these are all carboxylic acid derivatives. Highest Priority Groups: Carboxylic Acids, Sulfonic Acids, Esters, Acid Halides, Amides However this really is an example of something you have to either look up, memorize, or have a computer do for you. , although note that there is some correlation between the oxidation state of the carbon and the priority (more oxidized groups tend to be higher priority). However, if a ketone is present with an alcohol (example 3) then we will use the suffix, “-one” because ketones have a higher priority for nomenclature than alcohols. So in example #1 above, the suffix of the molecule will be “-oic acid”, not “-one”, because carboxylic acids are given higher priority. He functional group with the highest priority will be the one which gives its suffix to the name of the molecule. If you have a molecule with, say, a carboxylic acid and a ketone you consult the table. And so, IUPAC (think of the “Ministry of Magic”, but for chemists) has developed one. ![]() We need some kind of priority system for nomenclature. What do you do? What suffix do you give the molecule? But then you come across a molecule which has multiple functional groups. You’re familiar with the familiar naming suffixes like -ol, -ene, -ane, -oic acid and so on. Let’s say you’re trying to name a molecule. How To Determine Which Functional Group Has “Priority” For Naming Purposes
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