The previous discussion has focused on the carbon framework that characterizes organic compounds, and has provided a set of nomenclature rules that, with some modification, apply to all such compounds. Comments, questions and errors shouldbe sent to pages are provided to the IOCD to assist in capacity building in chemical education. This page is the property of William Reusch. This system, known as the Cahn-Ingold-Prelog rules, uses and elaborates the priority rules developed earlier. The relationship of the sequence-rule-preferred substituent at geminally substituted positions, relative to the reference group, is cited as c- or t-, as appropriate.Īn alternative system which specifies the absolute configuration of substituted carbon atoms may also be used. If none of the substituents is named as a suffix, then that substituent of the pair of substituents having the lowest number, and which is preferred by the sequence rule, is chosen as the reference group. When two different substituents are attached at the same position of a monocycle, then the lowest-numbered substituent named as a suffix is selected as reference group. The relative configuration of other substituents are then reported as cis ( c) or trans ( t) to the reference substituent. When one substituent and one hydrogen atom are attached at each of more than two positions of a monocycle, the steric relations of the substituents may be expressed by first identifying a reference substituent (labeled r) followed by a hyphen and the substituent locator number and name. The “chloro” prefix will go before “ methoxy” simply because of the alphabetical order.Nomenclature Examples Examples of the IUPAC Rules in Practice The halogen and ether can only be substituents with the corresponding prefixes. These are mainly the halides, ethers, and nitro groups.įor example, the following hypothetical compound contains a halogen, an alcohol, an ether and a carboxylic acid:

In the final name, they are simply placed in alphabetical order. There are some groups that are not considered in the priority list – they are always substituents and get a prefix. For example, alcohols have higher priority than amines and therefore, when naming a compound containing these two functional groups, the alcohol is designated with a suffix and gets the lower number: It is also noteworthy that if there is a functional group suffix and a substituent, the functional group suffix gets the lowest possible number. Number the parent chain starting from the highest priority group and add the substituent(s) alphabetically: Treat the ketone as a substituent and remember those are added with a prefix – oxo. The longest chain contains six carbons, so the hexane changes to hexane nitrile: In this case, it is the same as the functional group name – nitrile. The nitrile group stands higher than the ketone, therefore, the parent chain will take the suffix from the nitrile group. This table should be very self-explanatory and following the strategies, will give you the knowledge to name alcohols, aldehydes, nitriles, ketones, esters, carboxylic acids, present with different combinations in complex molecules. (I did need to dig in the IUPAC Blue Book for quite a while to clarify the priority of functional groups but also wanted to thank James at MOC for a helping post.)

Determine the group with a higher priority using the functional group priority table below: Let’s break this down to see how it works. The other groups are treated as substituents and added to the name with prefixes: Here is the trick – you need to identify the functional group with the highest priority and add a suffix (ending) of that functional group. If these two were separate, we’d name them as a ketone and a nitrile, but how do you name it when the two functional groups are in one compound? Naming a compound with more than one functional group is not as straightforward as it is for alkanes, alkyl halides or alkenes.įor example, how do you name a molecule that contains a nitrile and a ketone?

Functional groups table