Advanced Nomenclature

So that covers your base chain, but what if you have something besides hydrogen connected to your chain? That is where functional groups come into play. The functional groups replace a hydrogen on the base chain.

The most basic functional groups are actually just more alkanes. An alkane as a functional group is an alkyl. Their names are:

$\begin{matrix} \text{Number of Carbon}&\text{Alkyl Name}\\ 1&methyl\\ 2&ethyl\\ 3&propyl\\ 4&butyl\\ 5&pentyl\\ 6&hexyl\\ 7&heptyl\\ 8&octyl\\ 9&nonyl\\ 10&decyl\\ \end{matrix}$

All alkyl groups are just like their alkane forms, except they are missing a single hydrogen at one end. This serves as the connecting point to the hydrocarbon in question. Alkyls (or alkenyls or alkynyls) connected to alkanes or alkenes or alkynes are known as side-chains. We can start naming them.

Now we add the second methyl group at atom 3. The atoms can be counted either clockwise or counter-clockwise, it doesn’t matter. Gallery 10.3.1 shows many different ways to represent $1,3\text{-}dimethylcyclohexane$.

Sure, that’s the longest contiguous chain of carbon. However, the actual base chain in this molecule is:

The base chain is first the chain containing the most multiple bonds, and then the longest chain.

So what happens when we have two different functional groups?

In order to name a compound that has multiple side chains, we have to identify each one distinctly, as if it were the only functional group. Then, in the name, we need to order the side chains in alphabetical order, ignoring any counting prefixes. We still number the carbon from the direction that minimizes the first number of a multiple bond or functional group.

Example Problem 10.3.1

Draw out the following molecule:
$1\text{-}ethyl\text{-}5,5\text{-}dimethyl\text{-}1,3\text{-}cyclopentadiene$

Now for the complicated part. Non-alkyl functional groups. Entire classes are designed around understanding functional groups, so we will have to settle for only giving a brief overview.

First off, if you have a functional group that is not just a side-chain, you will have a suffix on your molecule. There is only one suffix per molecule (except those derived from alkenes and alkynes). The functional group with the highest precedence takes the suffix, and all others are delegated prefixes, to be arranged alphabetically with the side chains. Let’s first just

The simplest functional groups are the halogens. Halogens are of the lowest priority, so they never get suffixed. Instead, you will always seem them as a prefix. The prefix for halogens is in the form of:

$\begin{matrix} \text{Halogen}&\text{Prefix}\\ Fluorine&Fluoro-\\ Chlorine&Chloro-\\ Bromine&Bromo-\\ Iodine&Iodo- \end{matrix}$

A pretty simple format, isn’t it? The other functional groups aren’t so easily remembered, as they have both prefixes and suffixes. I will introduce them in order of increasing priority.

The amine group has the formula $R-NH_2$. As a prefix, it is known as $amino-$, and as a suffix it is known as $-amine$.

Example: $4\text{-}methyl\text{-}2\text{-}pentanamine$

The next highest priority is alcohols. This group has the form $R-OH$. Also in this group is the thiol $R-SH$, which is at a lower priority than the alcohol. Thiols have the prefix $sulfanyl-$ and the suffix $-thiol$. Alcohols have the prefix $hydroxy-$ and the suffix $-ol$.

Example: $3\text{-}sulfanyl\text{-}1\text{-}propanol$

Example: $2\text{-}amino\text{-}1\text{-}ethenethiol$

After alcohols, we find Ketones and Thiones. These are simply a doubly bonded oxygen or sulfur. Again, in this group, oxygen holds higher priority. This group has the form $R=O$ or $R=S$. Ketones have a prefix $oxo-$ and a suffix $-one$. Thiones have a prefix $sulfanylidene-$ (fun, isn’t it?) and a suffix $-thione$

Example: $4\text{-}sulfanylidene\text{-}6\text{-}dodecanone$

Example: $2,3\text{-}butanedithione$

Next up, we have aldehydes. These have the format $-CHO$. In an aldehyde, the carbon atom that comprises the aldehyde group is included in the base chain. The aldehyde prefix is $formyl-$ and its suffix is $-al$.

Example: $3\text{-}methyl\text{-}1,5\text{-}pentanedial$

Almost done! One step up in priority is the nitrile group, of the form $R-CN$. This group’s prefix is $cyano-$ and its suffix is $-nitrile$.

Example: $1,4\text{-}Butanedinitrile$

Finally we have the Carboxylic acids, of the form $R-COOH$. The prefix is $carboxy-$ and the suffix is $-oic\ acid$. Yes, the suffix added a separate word.

Example: $4\text{-}cyano\text{-}1\text{-}butanoic\ acid$

Now for all of that information in table form:

$\begin{matrix} \bold{Group}&\bold{Form}&\bold{Prefix}&\bold{Suffix}&\bold{Priority}\\ Carboxylic\ Acids&R-COOH&carbxy-&-oic\ acid&highest\\ Nitriles&R-CN&cyano-&-nitrile&|\\ Aldehyde&R-CHO&formyl-&-al&|\\ Ketones&R=O&oxo-&-one&|\\ Thiones&R=S&sulfanylidene-&-thione&|\\ Alcohol&R-OH&hydroxy-&-ol&|\\ Thiol&R-SH&sulfanyl-&-thiol&\downarrow\\ Amine&R-NH_2&amino-&-amine&lowest \end{matrix}$

One more thing is linkages. Sometimes you’ll encounter two groups, the ester and the ether.

Let’s start with the simpler one, the ether. An ether is when two independent carbon chains are linked by one oxygen, in the form $R_1-O-R_2$. In naming an ether, you pick the shorter chain, and replace the $-ane$ with $-oxy$, and append it to the beginning of the longer chain. A carbon number is needed if the ether is not connected to the end of the main chain.

Example: $Ethoxypropane$

Example: $2\text{-}ethoxypentane$

Example: $1,2,3\text{-}trimethoxyhexane$

Example: $2,5\text{-}dimethoxymethoxy\text{-}1\text{-}pentanol$

Those examples should be sufficient for covering the various types of ethers you might encounter. The typical rule is to work from the outside in for the chains of ethers. chained ethers bring up a scenario where the larger chain might come first. If your base chain is connected via ether to another ether, then the chain connected to the main chain will always be the last named chain of that group.

Basically, that just means that you can have the longer chain first, if it’s the outside of a series of ethers.

Example Problem 10.3.2

The other linkage we should look out for is the ester. An ester is a derivative of a carboxylic acid, so we will start there.

A carboxylic acid is a chain that ends in a specific group, the $COOH$ group. One simple carboxylic acid is $methanoic\ acid$:

Notice that the carbon in the carboxylic acid group counted towards the chain, making the chain only one long. This is the simplest carboxylic acid, and it will serve as the basis of our exploration of esters.

Let’s say we replace that hydrogen attached to the oxygen with another R-group, say butane. This gives us:

Now we have ourselves an ester. The ester is a bit different from the ether, as the group attached to the oxygen is always named first, as if it were any ol’ functional group. The group that contains the carbonyl (COO) group is named at the end, as its own word. You replace the suffix of this group with $-oate$ instead of $-oic\ acid$. This means that in the molecule above, our secondary group is the butane, and our primary group is the $methanoic\ acid$. This makes that molecule’s name $butyl\ methanoate$. This suffix is of a higher priority that any other group, and as such, the carbon involved in the carbonyl group is always numbered 1.

Here are a few more examples:

$2,4\text{-}hexadienyl\ 2,4\text{-}nonadienoate$:

$2\text{-}butynyl\ ethanate$:

$cyclohexyl\ propanoate$:

$heptan\text{-}3\text{-}yl\ 4\text{-}cyclopropyl\text{-}3\text{-}oxo\text{-}1\text{-}hexanoate$

$6\text-ethenoxy\text{-}1\text{-}hexen\text{-}3\text{-}yl\ 2,4,6,8\text{-}nonatetraynoate$: