A common "ane" suffix identifies these compounds as alkanes. Longer chain alkanes are well known, and their names may be found in many reference and text books.
The names methane through decane should be memorized, since they constitute the root of many IUPAC names. Fortunately, common numerical prefixes are used in naming chains of five or more carbon atoms. Some important behavior trends and terminologies: i The formulas and structures of these alkanes increase uniformly by a CH 2 increment.
Beginning with butane C 4 H 10 , and becoming more numerous with larger alkanes, we note the existence of alkane isomers. For example, there are five C 6 H 14 isomers, shown below as abbreviated line formulas A through E :.
Although these distinct compounds all have the same molecular formula, only one A can be called hexane. How then are we to name the others? The IUPAC system requires first that we have names for simple unbranched chains, as noted above, and second that we have names for simple alkyl groups that may be attached to the chains.
Examples of some common alkyl groups are given in the following table. Note that the "ane" suffix is replaced by " yl " in naming groups. The symbol R is used to designate a generic unspecified alkyl group.
Find and name the longest continuous carbon chain. Identify and name groups attached to this chain. Number the chain consecutively, starting at the end nearest a substituent group. Designate the location of each substituent group by an appropriate number and name. Assemble the name, listing groups in alphabetical order using the full name e. The prefixes di, tri, tetra etc. Halogen substituents are easily accommodated, using the names: fluoro F- , chloro Cl- , bromo Br- and iodo I-.
If the halogen is bonded to a simple alkyl group an alternative "alkyl halide" name may be used. Thus, C 2 H 5 Cl may be named chloroethane no locator number is needed for a two carbon chain or ethyl chloride. Halogenated alkyl substituents such as bromomethyl, BrCH 2 —, and trichloromethyl, CCl 3 —, may be listed and are alphabetized according to their full names. For additional examples of how these rules are used in naming branched alkanes, and for some sub-rules of nomenclature.
Cycloalkanes have one or more rings of carbon atoms. The simplest examples of this class consist of a single, unsubstituted carbon ring, and these form a homologous series similar to the unbranched alkanes. The last yellow shaded column gives the general formula for a cycloalkane of any size. If a simple unbranched alkane is converted to a cycloalkane two hydrogen atoms, one from each end of the chain, must be lost.
Alkyl groups are not independent molecules; they are parts of molecules that we consider as a unit to name compounds systematically. Name alkanes according to the LCC longest continuous chain of carbon atoms in the molecule rather than the total number of carbon atoms. This LCC, considered the parent chain, determines the base name, to which we add the suffix - ane to indicate that the molecule is an alkane.
If the hydrocarbon is branched, number the carbon atoms of the LCC. Numbers are assigned in the direction that gives the lowest numbers to the carbon atoms with attached substituents. Hyphens are used to separate numbers from the names of substituents; commas separate numbers from each other. Place the names of the substituent groups in alphabetical order before the name of the parent compound.
Identify all of the substituents groups appending from the parent chain. Number the carbons of the parent chain from the end that gives the substituents the lowest numbers. When compairing a series of numbers, the series that is the "lowest" is the one which contains the lowest number at the occasion of the first difference. If two or more side chains are in equivalent positions, assign the lowest number to the one which will come first in the name. If the same substituent occurs more than once, the location of each point on which the substituent occurs is given.
In addition, the number of times the substituent group occurs is indicated by a prefix di, tri, tetra, etc. If there are two or more different substituents they are listed in alphabetical order using the base name ignore the prefixes. The only prefix which is used when putting the substituents in alphabetical order is iso as in isopropyl or isobutyl. The prefixes sec- and tert- are not used in determining alphabetical order except when compared with each other. If chains of equal length are competing for selection as the parent chain, then the choice goes in series to: a the chain which has the greatest number of side chains.
A cyclic ring hydrocarbon is designated by the prefix cyclo- which appears directly in front of the base name. In summary, the name of the compound is written out with the substituents in alphabetical order followed by the base name derived from the number of carbons in the parent chain. Commas are used between numbers and dashes are used between letters and numbers. There are no spaces in the name. Here are some examples:. Alkyl halides The halogen is treated as a substituent on an alkane chain.
The halo- substituent is considered of equal rank with an alkyl substituent in the numbering of the parent chain. The halogens are represented as follows:. Alkenes and Alkynes - unsaturated hydrocarbons Double bonds in hydrocarbons are indicated by replacing the suffix -ane with -ene.
If there is more than one double bond, the suffix is expanded to include a prefix that indicates the number of double bonds present -adiene , -atriene , etc. Triple bonds are named in a similar way using the suffix -yne. The position of the multiple bond s within the parent chain is are indicated by placing the number s of the first carbon of the multiple bond s directly in front of the base name.
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