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NOMENCLATURE FOR ORGANIC CHEMISTRY Alkanes 1. Determine the longest continuous chain of carbons. The length of this chain determines the base name (see names below). 2. Any branched groups are named as an alkyl group. The alkyl group uses the same base name, but changes the ending to -yl (see names below). A few alkyls have special names**. 3. The complete name of the branched group(s) requires a number position corresponding to the carbon on the longest continuous chain identified in #1. The lowest combination of numbers is used when determining which end of the chain to begin the numbering. 4. When there are multiple branched groups of the same type, the Greek prefixes of di-, tri-, tetra-, penta-, etc. are used in front of the alkyl name. # of C 1 2 3 4 5 6 7 8 9 10 Formula CH4 CH3CH3 CH3CH2CH3 CH3(CH2)2CH3 CH3(CH2)3CH3 CH3(CH2)4CH3 CH3(CH2)5CH3 CH3(CH2)6CH3 CH3(CH2)7CH3 CH3(CH2)8CH3 Name Methane Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane Alkyl formula -CH3 -CH2CH3 -CH2CH2CH3 * * * * * * * Alkyl name Methyl Ethyl Propyl *the alkyl names do continue in the same trend, but are rare and we will not worry about them. **the (CH3)2CH- alkyl group is called isopropyl and the (CH3)3C- alkyl group is called t-butyl. CH3 ex) CH3 CH2 CH2 CH CH CH3 CH3 CH3 ex) CH3 CH2 CH2 CH2 C CH3 CH3 name: 2,3-dimethyl hexane name: 2,2-dimethyl hexane CH3 CH3 ex) CH3 CH2 CH C CH3 CH2 CH2 CH3 name: ??? CH3 ex) CH3 CH CH2 CH CH CH3 CH3 CH2 CH2 CH3 name: ??? ex) What is the condensed structural formula for: 2,2,3-trimethylpentane; 3-ethyl-2,5-dimethyloctane Functional Groups When a functional group is present, the suffix of the base name is altered according to the correct functional group present. A number in some cases is also needed to clarify any potential structural isomers. The suffixes are: Functional Group -OH -CHO -RR'C=O -COOH -C=C-C≡C- Suffix -ol -al -one -oic acid -ene -yne Numbering Required? more than 2 C's no (always C#1) more than 3 C's no (always C#1) more than 3 C's more than 3 C's Cycloalkanes These are ring structures where the two ends of the chain connect together. The most common ones are those with five and six carbon rings. Others are possible, but are not always as stable. Pictured below are the geometric symbols used to represent cyclopropane, cyclobutane, cyclopentane, and cyclohexane (respectively). As you can see, the name "cyclo" is placed in front of the base alkane name. Mono-substituted cycloalkanes do not require numbers as all positions on the ring are equivalent. Di-substituted cycloalkanes require numbers and may be numbered clockwise or counter-clockwise. A cycloalkene always has the location of the double bond in the C1-C2 position. Benzene derivatives These are molecules containing the benzene ring (C6H6) unit whose symbol is shown below. For mono-substituted benzene's, many have common names. A methyl group produces the molecule named Toluene, an -OH group produces the molecule named Phenol, and a -NH2 group produces the molecule named Aniline. For di-substituted benzenes, number is required or (old system) use of ortho, meta, and para substitution patterns are acceptable.