DAT Booster Organic Chemistry Ch 2. IUPAC Nomenclature PDF

Chapter 2 1 Organic Chemistry - IUPAC Nomenclature This chapter will cover the rules of IUPAC nomenclature – which is the accepted method for naming organic compo...

Chapter 2 1 Organic Chemistry - IUPAC Nomenclature This chapter will cover the rules of IUPAC nomenclature – which is the accepted method for naming organic compounds. The correct IUPAC name for a compound will distinguish its unique structure and stereochemistry. It is important to be able to convert between bond line structures and IUPAC names, as questions may appear in either form on your test. 1 Nomenclature Basics The parent chain is the longest continuous carbon chain in an organic compound. The rst step in assembling the compound’s complete IUPAC name is to determine the name of the parent chain. # of Carbons Pre x 1 meth- 2 eth- 3 prop- 4 but- 5 pent- 6 hex- 7 hept- 8 oct- 9 non- 10 dec- Alkanes “-ane” If an organic compound is a hydrocarbon with no carbon-carbon double or triple bonds, it is an alkane. Alkanes are named by adding the suffix “ane” to the parent chain. 1 3 5 2 4 6 7 Parent Chain: heptane Naming of alkanes. DAT Booster | Booster Prep™ fi fi Chapter 2 2 After identifying the parent chain, identify any substituents coming off of the parent chain. The parent chain should be numbered in the direction that assigns the substituents the lowest possible numbers. Alkyl Substituents Alkyl substituents (carbon chains) are named with the same prefixes as the parent chain. Simply count the carbon atoms, use the correct prefix, and add the suffix “yl”. If multiple substituents are present, list them in alphabetical order. If multiple of the same substituent are present, designate them with the prefixes “di”, “tri”, “tetra” and “penta”. Note, ignore these prefixes when listing substituents in alphabetical order. 1 2 8 6 4 7 5 3 3,6-diethyl-2,5-dimethyloctane Naming of molecules with alkyl substituents. Example 2.11: What is the IUPAC name of the following molecule? Solution: 6 4 2 7 5 3 1 3-ethyl-4-methylheptane Halogen Substituents Alkyl halides are alkanes with halogen substituents. When naming alkyl halides, we follow the same rules used for naming alkanes. The following prefixes are used to name halogen substituents: Halogen Name Fluorine (F) Fluoro- Chlorine (Cl) Chloro- Bromine (Br) Bromo- Iodine (I) Iodo- DAT Booster | Booster Prep™ Chapter 2 3 Cl 5 3 1 6 4 2 2-chloro-3-methylhexane Naming of molecules with halogen substituents. 2 Alkenes and Alkynes Carbon-carbon pi bonds are higher priority than alkyl or halogen substituents, so they will 1 determine the suffix of the parent chain. The parent chain must include the pi-bonded carbons and numbered to give the pi-bonded carbons the lowest locant possible. Place the number that locates the first carbon of the double/triple bond before the parent chain name or suffix. Alkenes “-ene” If the molecule has at least one carbon-carbon double bond, it is an alkene. Alkenes are named by adding the suffix “ene” to the parent chain. 2 5 3 1 6 4 5-methylhex-1-ene Naming of alkenes. Alkynes “-yne” If the molecule has at least one carbon-carbon triple bond, it is an alkyne. Alkynes are named by adding the suffix “yne” to the parent chain. 1 Br 5 3 4 2 5-bromopent-1-yne Naming of alkynes. Notice how in the previous example, the carbon bearing the bromine and the carbon bearing the triple bond are on opposite ends of the molecule. When deciding which carbon should receive the number ‘1’, functional group priorities must be taken into account. As previously stated, carbon- carbon double and triple bonds are a higher priority group than alkyl and halogen substituents. Therefore, carbon ‘1’ is the alkyne carbon on the right. DAT Booster | Booster Prep™ Chapter 2 4 Example 2.21: What is the IUPAC name of the following molecule? 1 F Solution: 1 9 7 5 3 F 10 8 6 4 2 10-fluoro-2-methyl-6-propyldec-1-ene 3 Cyclic Compounds Cyclic alkanes are named with the prefix “cyclo”, for example cyclohexane. Example 2.31: What is the IUPAC name of the following molecule? Cl Solution: Cl 3 4 2 5 1 6 4-chloro-1,2-dimethylcyclohexane Spiro Compounds Spiro compounds are compounds with two rings connected by a single carbon. To name a spiro compound: Count the number of carbons in each ring, excluding the spiro center (red). List the numbers from lowest to highest inside brackets. Add the prefix “spiro” before the brackets. Count the total number of carbons and write the alkane parent chain name after the brackets. DAT Booster | Booster Prep™ Chapter 2 5 spiro[3.4]octane spiro[5.5]undecane Naming of spirocyclic alkanes. Bicyclic Compounds Bicyclic compounds are compounds with two or more rings linked together by two bridgehead carbons (red). To name a bicyclic compound: Count the number of carbons in each ring, excluding the bridgehead carbons (red). List the numbers from highest to lowest inside brackets. Add the prefix “bicyclo” before the brackets. Count the total number of carbons and write the alkane parent chain name after the brackets. bicyclo[3.3.0]octane bicyclo[3.2.1]octane Naming of bicyclic compounds. 4 Carboxylic Acid Derivatives Before we continue learning about the nomenclature of additional functional groups, it is important to have the chart of functional group priorities for reference. When a molecule has multiple functional groups, the highest priority functional group determines the suf x of the parent chain. The parent chain must include the highest priority functional group, and it is numbered to give the highest priority functional group the lowest locant possible. DAT Booster | Booster Prep™ fi Chapter 2 6 Carboxylic acid derivatives include carboxylic acids, acid anhydrides, esters, acid halides, amides, and nitriles. As you can see in the functional group priority chart, carboxylic acid derivatives are the highest priority functional groups. Carboxylic Acids To name a carboxylic acid: Identify the longest carbon chain containing the carboxylic acid (parent chain). Name the parent chain and number the carbons. The parent chain of a carboxylic acid has the suffix “oic acid”. When assigning numbers to the carbon atoms, the carbonyl carbon of the carboxylic acid is always carbon 1, so it is not specified in the compound name. List the substituents in alphabetical order, followed by the parent chain. O Br 4 2 3 1 OH 4-bromo-2-methylbutanoic acid Naming of carboxylic acids. The procedure for the nomenclature of the other carboxylic derivatives is the same as the procedure for carboxylic acids, however, each derivative has its own unique suf x. Remember that the carbonyl carbon of the carboxylic acid derivative is assumed to be on carbon 1, so the number ‘1’ need not be specified. Acid Anhydrides While you are unlikely to encounter a nomenclature question involving acid anhydrides, it is worth reviewing just in case. The nomenclature of anhydrides is a bit different than the other carboxylic acid derivatives due to their unique structure. To name an acid anhydride: List each component carboxylic acid in alphabetical order without the word acid. Insert “anhydride” at the end of the name. O O O ethanoic propanoic anhydride (aka acetic propanoic anhydride) Naming of an acid anhydride. DAT Booster | Booster Prep™ fi Chapter 2 7 Esters Esters are named with the suffix “oate”. The alkyl group bonded to the ester oxygen is listed prior to the parent chain name, with the suffix “yl”. O O 4 2 4 2 5 3 1 O 5 3 1 O ethyl pentanoate methyl pentanoate Naming of carboxylic acid derivatives : Esters. Acid Halides Acid halides are named with the suffix “oyl halide”. O O 4 2 4 2 3 1 Cl 3 1 F 2-methylbutanoyl chloride 2-methylbutanoyl fluoride Naming of carboxylic acid derivatives : Acid Halides Amides Amides are named with the suffix “amide”. If alkyl groups are bonded to the amide nitrogen, they are specified with the locant “N”. O O 4 2 4 2 3 1 NH2 3 1 N butanamide N,N-dimethylbutanamide Naming of carboxylic acid derivatives : Amides Nitriles While nitriles do not contain a carbonyl group, they are still considered a carboxylic acid derivative. Nitriles are named by adding the suffix “nitrile” after the “-e” ending of the parent chain name (note that for the other carboxylic acid derivatives, “-e” is replaced by the appropriate suffix). N 1 3 5 2 4 2,4-dimethylpentanenitrile Naming of carboxylic acid derivatives : Nitriles. DAT Booster | Booster Prep™ Chapter 2 8 Cyclic Carboxylic Acid Derivatives Naming cyclic carboxylic acid derivatives is a bit different. For the DAT, you should be familiar with the nomenclature of cyclic carboxylic acids and amides, using the suffixes “carboxylic acid” and “carboxamide” respectively. O O OH NH2 cyclohexanecarboxylic acid cyclohexanecarboxamide Naming of cyclic carboxylic acid (left) and cyclic amide (right). Example 2.41: What are the IUPAC names of the following molecules? O O O N N Cl H HO O F F A B C D Solution: O 2 1 N O 1 2 4 3 propyl ethanoate 2-methylbutanenitrile A B O O N 1 3 2 4 Cl H 2 4 HO 1 3 F F 2-ethyl-N-methylbutanamide 4-chloro-2,2-difluorobutanoic acid C D DAT Booster | Booster Prep™ Chapter 2 9 5 Additional Functional Groups Next in the order of priority are aldehydes followed by ketones. While these compounds contain a carbonyl group, they are not carboxylic acid derivatives. Aldehydes To name an aldehyde: Identify the longest carbon chain containing the highest priority functional group (parent chain). Number the parent chain in the direction that gives the lowest possible locant to the highest priority functional group. If the aldehyde group is the highest priority functional group, name the parent chain by changing the final “-e” of the alkane name to an “al” suffix. When this is the case, the carbonyl carbon of the aldehyde is always carbon 1, so the locant is not specified in the compound name (except in the case of cyclic compounds). If the aldehyde group is not the highest priority group, the prefix “oxo” may be employed to name the group as a substituent. List the substituents in alphabetical order, followed by the parent chain name. O Cl 4 2 3 1 H 4-chloro-3-methylbutanal Naming of aldehydes. Aldehydes bonded to hydrocarbon rings are named with the suffix “carbaldehyde” after the parent chain name. In the case of multiple substituents, the locant 1 must be specified. O 5 2 3 1 H 4 6 5 3-methylcyclohexane-1-carbaldehyde Naming of a carbaldehyde. Ketones To name a ketone: Identify the longest carbon chain containing the highest priority functional group (parent chain). Number the parent chain in the direction that gives the lowest possible locant to the highest priority functional group. The parent chain of a ketone has the suffix “one”. If the ketone group is the highest priority functional group, name the parent chain by changing the final “-e” of the alkane name to an “one” suffix. Place the number that locates the ketone functional group before the parent chain name or suffix. If the ketone group is not the highest priority group, the prefix “oxo” may be employed to name the carbonyl group as a substituent. List the substituents in alphabetical order, followed by the parent chain name. DAT Booster | Booster Prep™ Chapter 2 10 O Cl 5 4 3 2 1 5-chloropentan-2-one Naming of ketones. Example 2.51: What is the IUPAC name of the following molecule? Cl O Br H Solution: ClCl OO 44 22 Br Br 55 33 1 1H H 5-bromo-3-chloropentanal 5-bromo-3-chloropentanal Example 2.52: What is the IUPAC name of the following molecule? O Solution: O 1 5 2 4 3 2-propylcyclopentan-1-one After carbonyl containing compounds, alcohols are the next highest priority functional group, followed by amines. Alcohols A molecule with a hydroxyl substituent (-OH) is an alcohol. To name an alcohol: Identify the longest carbon chain containing the highest priority functional group (parent chain). Number the parent chain in the direction that gives the lowest possible locant to the highest priority functional group. If the hydroxyl group is the highest priority functional group, name the parent chain by changing the final “-e” of the alkane name to an “ol” suffix. Place the number that locates the hydroxyl group before the parent chain name or suffix. DAT Booster | Booster Prep™ Chapter 2 11 If the hydroxyl group is not the highest priority group, the prefix “hydroxy” may be employed to name the -OH group as a substituent. List the substituents in alphabetical order, followed by the parent chain. OH 2 1 O 3 4 3 4 2 2 1 OH HO 3 1 H 2-ethyl-3-methylcyclobutan-1-ol 3-buten-1-ol 3-hydroxypropanal Naming of alcohols. Amines Amines consist of nitrogen with three single bonds to hydrogen or carbon atoms. The simplest amine is ammonia (NH3). When the hydrogens are replaced with alkyl groups, the result is a primary, secondary, or tertiary amine: N N N H H H primary secondary tertiary amine amine amine A primary (left), secondary (middle), and tertiary (right) amine. To name an amine: Identify the longest carbon chain containing the highest priority functional group (parent chain). Number the parent chain in the direction that gives the lowest possible locant to the highest priority functional group. If the amine is the highest priority functional group, name the parent chain by changing the final “-e” of the alkane name to an “amine” suffix. Place the number that locates the amine group before the parent chain name or suffix. If the amine group is not the highest priority group, the prefix “amino” may be employed to name the amine group as a substituent. List the substituents in alphabetical order, followed by the parent chain. An alkyl substituent on the amine nitrogen is specified with the locant ’N’. 4 2 3 1 N N,N-dimethylbutan-1-amine Naming of amines. DAT Booster | Booster Prep™ Chapter 2 12 Ethers A molecule with an oxygen single bonded to two carbon atoms is an ether. Ethers are named by the same convention as alkyl substituents, except with prefix “alkoxy”. Br O Cl 1 2 3 3 1 O 6 5 4 2 2-chloro-1-methoxypropane 1-bromo-3-propoxycyclohexane Naming of ethers. Nitro Groups Nitro groups are named by the same convention as halogen substituents, except with the prefix “nitro”. NO2 5 3 1 4 2 4-nitropent-1-yne Naming of molecules with a nitro group. Sulfur-Containing Compounds Thiols (-SH), or mercaptans, are sulfur analogs of alcohols (-OH). Thiol groups are named by the same convention as alcohols, except with the suffix “thiol” when it is the highest priority functional group and the prefix “mercapto” when the thiol is not the highest priority functional group. Sulfides (RSR’) are sulfur analogs of ethers (ROR’). Sulfides are named by the same convention as alkyl substituents, except with prefix “alkylthio”. Sulfonic acids (-SO3H) are named with the suffix “sulfonic acid” when it is the highest priority functional group and “sulfo” when the sulfonic acid is not the highest priority functional group. Naming of sulfur-containing compounds. DAT Booster | Booster Prep™ Chapter 2 13 Example 2.53: What are the IUPAC names of the following molecules? OH Br O N F H NO2 A B C D Solution: OH Br 1 3 5 6 4 2 2 4 6 5 3 1 NO2 5-methylhex-5-en-2-ol 3-bromo-2-nitrohexane A B 4 2 4 2 5 3 1 O 3 1 N F H 1-ethoxy-4-fluoropentane N-ethylbutan-1-amine C D 6 Benzene Derivatives To name a benzene derivative, first examine the substituent(s). For mono substituted benzene derivatives, the substituent name is simply written before the word “benzene”. NO2 Br Cl nitrobenzene bromobenzene ethylbenzene chlorobenzene Naming of mono substituted benzene derivatives. Some benzene derivatives have special names, shown below. The only accepted name for benzene directly bound to an aldehyde group is benzaldehyde, and the only accepted name for benzene directly bound to a carboxylic acid is benzoic acid. These names are important to recognize for the DAT. DAT Booster | Booster Prep™ Chapter 2 14 O O NH2 H OH benzaldehyde aniline benzoic acid (aminobenzene) O OH toluene anisole phenol styrene (methylbenzene) (methoxybenzene) (hydroxybenzene) (vinylbenzene) Important benzene derivatives. When there are multiple substituents on the benzene ring, the higher priority substituent determines the name of the parent chain and is placed on carbon 1. The other substituent is named with the usual nomenclature rules, preceded by the necessary locant. O Cl Cl O OH HO O 4-methoxyphenol H 1,3-dichlorobenzene 2-methylbenzoic acid 3-ethylbenzaldehyde Naming of benzene rings with functional groups of different priorities. Example 2.61: Name the following benzene derivatives: Br Br Br A. O O B. O NO2 O C. NO2 O NO2 O OH OH OH Cl Cl Cl Br Br Br Cl Cl Cl Solution: A A B A B Br C Br B C C Br A. O O O B. NONO C. 2 O2 ONO2 O OHOH OH Cl Cl Cl Br Br Br Cl Cl Cl 1-bromo-3-methoxybenzene 1-bromo-3-methoxybenzene 4-bromo-1,2-dichlorobenzene 1-bromo-3-methoxybenzene 4-bromo-1,2-dichlorobenzene 2-nitrobenzoic 4-bromo-1,2-dichlorobenzene acidacid acid 2-nitrobenzoic 2-nitrobenzoic (3-bromoanisole) (3-bromoanisole) (3-bromoanisole) A A A B B B C C C DAT Booster | Booster Prep™ Chapter 2 15 7 Guide to Nomenclature 1. Identify the Parent Chain Identify the longest carbon chain containing the highest priority functional group. The parent chain must include the highest priority functional group, so the longest carbon chain might not be the parent chain. HO HO 1 5 3 1 3 5 7 4 2 2 4 6 parent chain is longest chain 5 carbons long is 7 carbons long 5-carbon chain (left) vs. 7-carbon chain (right). Parent chain is the longest carbon chain containing the highest priority functional group. If there are multiple possibilities for the parent chain, the one with more substituents will be designated the parent chain. 6 1 5 2 3 1 3 2 4 4 5 6 3 substituents 2 substituents parent chain Carbon chain with 3 substituents (left) vs. carbon chain with 2 substituents (right). Parent chain is the chain with more substituents. 2. Number the Carbons Number the parent chain in the direction that gives the lowest locants to the functional groups (the lowest set of numbers). 3 4 2 5 1 6 Br 1-bromo-4-ethyl-2-methylcyclohexane locants: 1, 2, and 4 2 6 5 incorrect 1 3 5 1 4 5 6 4 4 2 3 1 numbering 5 Br 3 Br 2 Br options: locants: 1, 3, and 4 locants: 1, 2, and 5 locants: 1, 4, and 5 Numbering the carbons on the parent chain based on position of functional groups. DAT Booster | Booster Prep™ Chapter 2 16 If there is a high priority functional group (higher priority than alkyl, halogen, nitro, and/or ether substituents), then the highest priority functional group receives the lowest possible locant. 2 4 F HO 2 4 F 1 2 4 F 1 3 3 3 O F 1 F F 4,4-difluorobutan-2-one 4,4-difluorobutan-2-ol 4,4-difluorobut-1-ene carbon 1 is NOT the fluorine-bearing carbon becasue there are higher priority functional groups Numbering the carbons on the parent chain based on priority of functional groups. If there is a tie between alkyl, halogen, nitro, and/or ether substituents, assign priority in the direction which gives the lower locants to the substituent that comes first alphabetically. 1 2 3 4 5 6 7 Br O 3-bromo-5-methoxyheptane number to put the bromo substituent on carbon 3 instead of the methoxy substituent bromo comes before methoxy alphabetically Numbering the carbons on the parent chain alphabetically between certain functional groups. 3. Assemble the Full Name Assemble the full IUPAC name by listing the substituents in alphabetical order, followed by the parent chain name. Remember some functional groups (alcohols, aldehydes, ketones, carboxylic acid derivatives and more) are named with suffixes after parent chain. O 1 2 3 4 5 6 Br F Cl 6-bromo-4-chloro-2-fluorohexan-3-one substituents listed alphabetically (‘b’ before ‘c’ before ‘f’) note: the compound is numbered to give the highest priority group the lowest locant possible Full IUPAC name of 6-bromo-4-chloro-2- fluorohexan-3-one. DAT Booster | Booster Prep™