IUPAC Rules because that Alkane NomenclatureHalogen GroupsThree Rules for Naming AlkanesExercises

After completing this section, you should be may be to

carry out the correct IUPAC name for any type of given alkane structure (Kekulé, condensed or shorthand). Attract the Kekulé, condensed or shorthand framework of an alkane, offered its IUPAC name.

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The IUPAC system of nomenclature intends to ensure

the every necessary compound has a unique, unambiguous name. That the IUPAC surname of any compound conveys the framework of that compound to a person familiar with the system.

One means of checking whether the name you have provided to one alkane is reasonable is to count the variety of carbon atoms implied by the liked name. Because that example, if you called a link 3‑ethyl-4‑methylheptane, you have actually indicated that the compound consists of a full of 10 carbon atoms—seven carbon atoms in the key chain, 2 carbon atoms in one ethyl group, and one carbon atom in a methyl group. If you were to examine the given structure and also find 11 carbon atoms, friend would know that you had made a mistake. Perhaps the name you should have written was 3‑ethyl-4,4‑dimethylheptane!

When specify name alkanes, a typical error of start students is a failure to choose out the longest carbon chain. Because that example, the correct name for the link shown below is 3‑methylheptane, not 2‑ethylhexane.

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IUPAC Rules because that Alkane Nomenclature

Find and also name the longest continuous carbon chain. Identify and name teams attached come this chain. Number the chain consecutively, beginning at the finish nearest a substituent group. Clues the ar of every substituent group by an ideal number and also name. Assemble the name, listing teams in alphabet order. The prefixes di, tri, tetra etc., supplied to designate several teams of the exact same kind, are not thought about when alphabetizing.

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The same principle can be applied to any type of of the straight chain alkane names provided in the table below.

NameMolecular FormulaCondensed structure Formula
Methane CH4 CH4
Ethane C2H6 CH3CH3
Propane C3H8 CH3CH2CH3
Butane C4H10 CH3(CH2)2CH3
Pentane C5H12 CH3(CH2)3CH3
Hexane C6H14 CH3(CH2)4CH3
Heptane C7H16 CH3(CH2)5CH3
Octane C8H18 CH3(CH2)6CH3
Nonane C9H20 CH3(CH2)7CH3
Decane C10H22 CH3(CH2)8CH3
Undecane C11H24 CH3(CH2)9CH3
Dodecane C12H26 CH3(CH2)10CH3
Tridecane C13H28 CH3(CH2)11CH3
Tetradecane C14H30 CH3(CH2)12CH3
Pentadecane C15H32 CH3(CH2)13CH3
Hexadecane C16H34 CH3(CH2)14CH3
Heptadecane C17H36 CH3(CH2)15CH3
Octadecane C18H38 CH3(CH2)16CH3
Nonadecane C19H40 CH3(CH2)17CH3
Eicosane C20H42 CH3(CH2)18CH3

What is the name of the monitor molecule?

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Solution

Rule #1: pick the longest, many substituted carbon chain include a useful group. This instance does no contain any functional groups, so we only should be involved with choosing the longest, most substituted carbon chain. The longest carbon chain has actually been emphasize in blue and consists that eight carbons.

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Rule #2: Carbons bonded to a functional team must have actually the lowest possible carbon number. If there room no practical groups, then any type of substitute present must have the lowest possible number. Since this example does no contain any type of functional groups, we only have to be came to with the two substitutes present, the is, the two methyl groups. If we start numbering the chain from the left, the methyls would certainly be assigned the numbers 4 and also 7, respectively. If we begin numbering the chain indigenous the right, the methyls would certainly be assigned the numbers 2 and also 5. Therefore, to accomplish the 2nd rule, numbering begins on the ideal side that the carbon chain as displayed below. This offers the methyl groups the lowest possible numbering.

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Solution

Rule #1: pick the longest, most substituted carbon chain containing a functional group. This example contains two practical groups, bromine and chlorine. The longest carbon chain has actually been highlighted in blue and consists of 7 carbons.

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Rule #2: Carbons bonded to a functional group must have the lowest feasible carbon number. If there space no sensible groups, then any kind of substituent current must have actually the lowest feasible number. In this example, number is numbered the chain from either the left or the appropriate would accomplish this rule. If us number the chain native the left, bromine and chlorine would certainly be assigned the 2nd and sixth carbon positions, respectively. If us number the chain from the right, chlorine would certainly be assigned the 2nd position and also bromine would certainly be assigned the sixth position. In various other words, whether we choose to number indigenous the left or right, the functional groups occupy the 2nd and 6th positions in the chain. To pick the correct numbering surbanbreathnyc.come, we need to utilize the 3rd rule.

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Rule #3: After using the first two rules, take it the alphabetical order into consideration. Alphabetically, bromine comes before chlorine. Therefore, bromine is assigned the 2nd carbon position, and chlorine is assigned the sixth carbon position.

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The surname of this molecule is: 2-bromo-6-chloroheptane


What is the name of the follow molecule?

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Solution

Rule #1: select the longest, many substituted carbon chain include a sensible group. This example includes two useful groups, bromine and also chlorine, and one substitute, the methyl group. The longest carbon chain has actually been highlighted in blue and consists of seven carbons.

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b) The structure that deserve to be drawn for the improper surname is shown listed below on the left. When you renumber it correctly (structure on the right), notice that the longest chain is 6 C’s and we begin the numbering on the finish to the best to make the methyl substituent come off at C-3 (instead that beong in ~ C-4 if we numbered the the the opposite direction) the exactly name must be 3-methyl hexane.