Basic Organic Chemistry Nomenclature CHEM 104 B/D

I have gone ahead and compiled all of the basic naming rules that we will be dealing with into one worksheet. I hope this will be helpful to you as you work through the assigned homework, LON CAPA, and as you prepare for quizzes/exams. This may seem like a lot of material to go through when you first see it, but as you practice this process will become second nature. Please let me know if there are things that aren’t clear or if you have suggestions to improve this worksheet. Thanks! Dr. Ray

Some Background

Naming organic molecules reminds me a bit of looking at a big old oak tree in the dead of winter. You had a huge trunk with a bunch of different branches coming out of it. Naming organic molecules is kind of the same. You have one main chain (the trunk) and lots of different substituents (branches) coming off the main chain. To get started with naming, the first things that you need to know are the basic names for carbon chains (See Table 1). This table also lists how you would describe these chains when they are substituents (coming off the main chain). Additionally, there are a series of often used functional groups that are still referred to using their common names. These are groups that you should commit to memory (Figure 1). Table 1. Names for Basic Carbon Chains and Substituents. # of C Name Formula Substituent Formula 1 methane CH4 methyl CH3- 2 ethane CH3CH3 ethyl CH3CH2- 3 propane CH3CH2CH3 propyl CH3CH2CH2- 4 butane CH3(CH2)2CH3 butyl CH3(CH2)2CH2- 5 pentane CH3(CH2)3CH3 pentyl CH3(CH2)3CH2- 6 hexane CH3(CH2)4CH3 hexyl CH3(CH2)4CH2- 7 heptane CH3(CH2)5CH3 heptyl CH3(CH2)5CH2- 8 octane CH3(CH2)6CH3 octyl CH3(CH2)6CH2- 9 nonane CH3(CH2)7CH3 nonyl CH3(CH2)7CH2- 10 decane CH3(CH2)8CH3 decyl CH3(CH2)8CH2-

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Figure 1. Common Substituents that You Should Commit to Memory

R

Isopropyl (iso counts for alphabetizing)

R

secondary butyl (sec-butyl)

(sec does not count for alphabetizing)

R

tertiary butyl (tert-butyl)

(tert does not count for alphabetizing)

R

Isobutyl (iso counts for alphabetizing)

R

vinyl

R

allyl

Naming Basic Organic Molecules

(or how I would go about this if I were in your shoes) Step 1. Determine the base name suffix of the molecule The base name of a molecule is determined by the functional groups present. Certain functional groups have been given higher priority than others (See Table 2). Your first step in naming a compound should be to identify all functional groups, and then determine which functional group has the highest priority. You then use the appropriate functional group specific base name (See Table 2). Step 2. Pick the longest continuous carbon chain in the molecule that contains the highest priority functional group (or contains a carbon that the highest priority group is attached to). Make sure to evaluate all potential options. Don’t just look “left to right,” often the longest chain will have you looking all around the molecule. The highest priority functional group must be part of this longest chain. If there is more than one way to make the longest continuous carbon chain containing the highest priority functional group, choose the chain that gives the greater number of substituents. Step 3. Form the base name for the molecule. Using the number of carbons in the longest chain that you chose in Step 2 and the appropriate suffix based on your functional group and Table 2, you can determine the base name of the molecule. If we had a carboxylic acid with a six carbon chain we would use “hexane” and replace the “e” of the -ane suffix with –oic acid to give hexanoic acid.

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Table 2. Functional Group Priorities and Naming Priority Functional

Group Prefix

(to be used if naming this functional group as a substituent)

Base Name Suffix (to be used when this group is

highest priority and the base name)

I Carboxylic Acids None -oic acid Aldehydes None -al Ketones None -one Esters None -oate

II Alkenes None -ene

III Alkynes None -yne

IV Alcohols hydroxy- -ol

Diols hydroxy- -base name of alkane-diol Amines amino- -amine Ethers alkoxy- (ex. methoxy) -ether (space between

substituents and ether) Halogens Fluoro-, chloro-, etc… none (will always be a

substituent, use –ane as the base name)

V Alkanes alkyl (ex methyl) -ane Step 4. Number the carbon chain. In order to classify a molecule that has substituents, you need to know what carbons the substituents are attached to. You MUST number the carbon chain (and only the carbons!) consecutively in the following manner: a. If the molecule has a functional group of priority I – IV (Table 2), start numbering the

chain on the side closest to the highest priority functional group. If there is more than one of the highest priority substituents, start numbering on the side where a highest priority substituent is closest to the end of the chain. If the highest priority substituents are the same distance to the end of the chain, start numbering on the side that has a substituent closest to it.

b. If the molecule is an alkane (priority V), start numbering the molecule on the side closest

to the first substituent. This will ensure that your numbers will be as low as possible. (If the distance to the first substituent is the same from each side, choose the side that is closest to the second substituent).

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Step 5. Describe all substituents that are attached to the main chain and any higher priority functional groups that are part of or attached to the chain. You must indicate the position of the highest priority substituent as well as any other substituents that are present in the molecule you are naming. It is often useful to make a list of the functional groups and substituents that are present on the molecule you will be naming. Use the following rules to help you create a list: If you have a functional group that is in: Priority I: Carboxylic Acids and Aldehydes: these functional groups are always attached to the end of the carbon chain, so you do not need to indicate what carbon these functional groups are attached to (there are a few exceptions, but we won’t see them in this class). Esters: these groups are named such that you will not have to indicate what carbon the ester is attached to (see exceptions to Step 6). Ketones: indicate what carbon the ketone is attached to by giving the carbon # directly before the base name (ex. 3-butanone) Priority II and III: Indicate where the multiple bonds are present by giving the lowest numbered carbon of the multiple bond before the base name (ex. 2-pentene) Priority IV: Alcohols, Diols, Amines, and Ethers: if a higher priority functional group is present, name the priority IV group as a substituent using the prefix listed in Table 2. If the priority IV group is the highest priority indicate what carbon the alcohol, diol alcohols, or amine is attached to by giving the carbon # directly before the base name (ex. 3-hexanol). When ethers are the highest priority substituent there is an exceptions (see Step 6). Halogens: always use as a substituent. Priority V: Alkanes: name substituents as alkyl groups. -If a substituent or functional group occurs more than once, use di-, tri-, tetra-, penta-, hexa-, etc. -You still must tell what carbon each substituent or functional group is attached to (if you have 2 or something use “di” and two numbers to indicate where those 2 groups are)! -Use dashes between numbers and letters -Use a comma between numbers Examples: 2,3-dichloroheptane, 1,3-heptadiene, 4,7-dihydroxyoctanoic acid

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Step 6. Put everything together and name it. Regardless of the order that the substituents are found on the molecule, list the substituents in alphabetical order before the base name. (Iso counts for alphabetical order. All others (di, tri, etc…tert, sec, etc.) do not) Again, use dashes between numbers and letters and use a comma between numbers. Like everything else, there are some exceptions to these rules. Ethers: name the two alkyl groups that are attached to the oxygen as substituents. List them in alphabetical order with a space in between the two names and finish with “a space” then ether. (ex. ethyl methyl ether, diethyl ether, methyl propyl ether) Amines: name the alkyl groups that are attached to the nitrogen as substituents (don’t worry about hydrogen). List them in alphabetical order and end with “amine.” No spaces between any of these names. (ex. triethylamine, diethylmethylamine, diisopropylamine) Esters: name the R group attached to the single bond oxygen as a substituent. Put this in the very beginning of the name. Add one space, and then name the carbon chain attached to the carbonyl carbon using the ester suffix –oate. (ex. methyl butanoate, ethyl propanoate) Diols: the only thing that is a bit different about diols is how you put everything together at the end. Keep the base name the same (don’t drop the “e”), then indicate where the OH groups are present, and add diol at that end (ex. 2-methylhexane-2,4-diol).