CHAPTER 13: Unit 3. Nomenclature
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Learning ObjectivesName alcohols with both common names and IUPAC names.Alcohols: The IUPAC names of simple alcohols end in -ol and their carbon chains are numbered to give precedence to the location of the -OH group. When a -OH group is bonded toa ring, ring is numbered beginning with the group. Alcohol common names contain the word alcohol preceded by the name of the alkyl group.Name the longest carbon chain to which the hydroxyl group is attached. The chain name is obtained by dropping the final -e from the alkane name and adding the suffix -ol.Number the chain starting at the end nearest to the hydroxyl group and use the appropriate number to indicate the position of -OH group. In numbering the longest carbon chain, the hydroxyl group has precedence over double and triple bonds as well as alkyl, cycloalkyl and halogen substitute.name and locate any other substituent present.In alcohols where the -OH group is attached to a carbon atom in a ring, the ring is numbered beginning with -OH group. Numbering then proceeds in a clockwise or counterclockwise direction to five the next substituent the lowest number. The number “1” is omitted from the name since by definition the hydroxyl bearing carbon is carbon 1.When -OH group is a substituent rather than main functional group in a molecule, the group is called hydroxy group. Example: Draw the structure for each compound.2-hexanol3-methyl-2-pentanolSolutionThe ending –ol indicates an alcohol (the OH functional group), and the hex– stem tells us that there are six carbon atoms in the LCC. We start by drawing a chain of six carbon atoms: –C–C–C–C–C–C–.The 2 indicates that the OH group is attached to the second carbon atom. Finally, we add enough hydrogen atoms to give each carbon atom four bonds. The ending –ol indicates an OH functional group, and the pent– stem tells us that there are five carbon atoms in the LCC. We start by drawing a chain of five carbon atoms:–C–C–C–C–C–The numbers indicate that there is a methyl (CH3) group on the third carbon atom and an OH group on the second carbon atom. |
Other Examples: |
| Cyclohexanol( 3D structure)To assign a common name:Name all the carbon atoms of the molecule as a single alkyl group.Add the word alcohol separating the word with a space. |
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| Besides being the name of the family of compounds, phenol is also the IUPAC approved name for the simplest member of the phenol family of compounds. Common names of phenols are also very popular. Methyl phenols are cresols. Hydroxy phenols are named based on the position of the second -OH group.IUPAC rules for naming phenols are simply extensions of the rules used to name benzene derivatives wit hydrocarbon or halogen substituents. |
| For hydroxyphenols, each of three isomers has a different common name. Hydroquinone |
| Resorcinol |
Homework Exercises1. Name each compound.a. b. 2. Name each compound.a. b. 3. Draw the structure for each compound.a. m-iodophenolb. p-methylphenol (p-cresol) 4. Draw the structure for each compound.a. 2,4,6-trinitrophenol (picric acid)b. 3,5-diethylphenolAnswers1.a. o-nitrophenolb. p-bromophenol 3.a. b. Ethers:Learning ObjectivesName simple ethers.Simple ethers are usually assigned with common names. To do so, both alkyl groups bonded to oxygen atoms are named and arranged alphabetically and then added the word-ether.More complex ethers are named using the IUPAC system. One alkyl group is named as a hydrocarbon chain, and the other is named as part of a substituted bonded to that chain.Step#1: name the simpler alkyl group attached to Oxygen of ether as an alkoxy substituent by changing the -yl ending of the alkyl group to -oxyCH3O- : methoxy CH3CH2O-: Ethoxy Step#2: name the remaining alkyl group as an alkane, with the alkoxy group as a substituent bonded to this chain. |
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ExampleWhat is the common name for each ether?CH3CH2CH2OCH2CH2CH3 SolutionThe carbon groups on either side of the oxygen atom are propyl (CH3CH2CH2) groups, so the compound is dipropyl ether.The three-carbon group is attached by the middle carbon atom, so it is an isopropyl group. The one-carbon group is a methyl group. The compound is isopropyl methyl ether.Homework ExerciseWhat is the common name for each ether?CH3CH2CH2CH2OCH2CH2CH2CH3 |
| Thiols: To name a thiol in IUPAC system:Name the parent hydrocarbon as an alkane and add the suffix thiol.Number the carbon chain to give the -SH group the lower number. |
| IN CLASS PRACTICE PROBLEMS: |
| What is the structure of 6-methyl-3-heptanol?Write the name of the following compound. |
| HOMEWORK EXERCISEName each alcohol and classify it as primary, secondary, or tertiary.a. CH3CH2CH2CH2CH2CH2OH b. c. Name each alcohol and classify it as primary, secondary, or tertiary. a. b. c. Draw the structure for each alcohol.3-hexanol3,3-dimethyl-2-butanolcyclobutanol Draw the structure for each alcohol.cyclopentanol4-methyl-2-hexanol4,5-dimethyl-3-heptanolAnswers1.1-hexanol; primary3-hexanol; secondary3,3-dibromo-2-methyl-2-butanol; tertiary 3.a. b. c. |
| Isomerism in Alcohol: Constitutional isomerism is possible for alcohols containing three or more carbon atoms. As with alkenes, both skeletal and positional isomers are possible.The C5 isomers are: Constitutional isomers for 4-carbon alcohol:1-butannol or butyl alcohol 2-methyl-1-propanol or isobutyl alcohol2-butanol or sec-butyl alcohol2-methyl-2-propanol or tert-butyl alcohol |
| isomerism in ether: ethers contain two carbon chains (two alkyl groups) unlike one carbon chain in alcohols. Constitutional isomerism possibilities depend on 1) partitioning of carbon atoms between the two alkyl groups 2) isomerism possibilities for the individual alkyl groups.Functional group isomerism: ethers and alcohols with the same number of carbon atoms and same degree of saturation have the same molecular formula. Functional group isomers are constitutional isomers that contain different functional groups. For example dimethyl ether and ethyl alcohol. dimethyl ether ethyl alcohol |
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