The first thing we want to do is to find the longest chain. So, thereвЂ™s no dash, or space, or comma, or anything else between the parentheses of the complex substituent and the rest of the molecule as we treat the parentheses as a вЂњletterвЂќ for the purposes of nomenclature. We are still using the same principles weвЂ™ve learned in the last tutorial: we use commas between numbers and dashes between the numbers and letters. Notice how we enclosed the complex substituent in the parentheses. So, the name for this compound is 1-ethyl-3-(1-methylbutyl)cyclohexane. This also gives it precedence over the complex substituent for the numbering preferences since we donвЂ™t have the more substituted atom in this cycle. And since вЂњeвЂќ is before вЂњmвЂќ in the alphabet, the ethyl group will be first in the name. So, in this case, we have вЂњeвЂќ in ethyl vs вЂњmвЂќ in the complex substituent. The very first letter in the parentheses will count for the alphabetical order regardless of what it may be (a prefix or anything like that). HereвЂ™s something important about what counts for the alphabet in the complex substituents. Now, weвЂ™ll need to arrange those groups alphabetically in the name. The bottom group is the one that we have just looked at: 1-methylbutyl. Next, the branch on the top is a simple ethyl group. Thus, our parent is going to be cyclohexane. In this case, itвЂ™s going to be the ring itself. The first rule of the nomenclature is to find the longest continuous chain. Here we have a 6-membered ring with two branches. The parentheses are not optional here, so make sure you donвЂ™t forget about those on the test! Also, to specify that this is a complex substituent, we are going to enclose it in the parentheses. Then, we say that thereвЂ™s a methyl group in the 1 st position here and put together the rest of the name. We then find the longest chain, which in this case is a 4-carbon chain. WeвЂ™ll number at the carbon where it connects to the parent molecule.

Then, weвЂ™ll change the ending -ane to -yl to signify that this is still a branch or a substituent and not a molecule. This is where the IUPAC steps in and tells us the rule: we start numbering at the place of attachment, find the longest chain, and name the rest of the branch as if it was a standalone molecule. Now, how about the other two? Should we use вЂњsecвЂќ or maybe вЂњisoвЂќ or something else? So, as we know from the last tutorial, itвЂ™s going to be just a simple pentyl group. This branch is connected at the very end of the chain and doesnвЂ™t have any extra branches sticking off it. How about something more complicated that we canвЂ™t commit to memory? Systematic Rules for Complex SubstituentsДЄlright, so those were the simple cases that you just have to memorize. Finally, any numeric prefixes like di-, tri- tetra-, etc. If the prefix modifies the structure and is spelled together, like cyclo- or iso- among the ones weвЂ™ve already seen, it will count. If the prefix is spelled through the dash, it definitely wonвЂ™t count. HereвЂ™s a quick rule of thumb you can remember about which prefixes count and which ones donвЂ™t. But you will need to memorize those names and their corresponding structures for the test.ДЄlso, just like in the case with isopropyl, the вЂњi-вЂќ in the isobutyl will count for the alphabetical order while other prefixes wonвЂ™t. Again, those are the traditional names, so you donвЂ™t have to remember the logic behind why thereвЂ™s a вЂњsecвЂќ or a вЂњtertвЂќ prefix. The prefix вЂњsecвЂќ stands for secondary, while the prefix вЂњtertвЂќ stand for tertiary. WeвЂ™ve got a normal butyl group, the sec-butyl, the isobutyl, and tert-butyl.

Organic chemistry nomenclature examples