Notes on Nomenclature and Isomerism | Grade 11 > Chemistry > Alkanes | KULLABS.COM

Nomenclature and Isomerism

  • Note
  • Things to remember

Nomenclature

The IUPAC nomenclature system is a set of logical rules devised and used by organic chemists to circumvent problems caused by arbitrary nomenclature.

In general, an IUPAC name will have three essential features:

  • A root or base indicating a major chain or ring of carbon atoms found in the molecular structure.
    A suffix or other element(s) designating functional groups that may be present in the compound.
    Names of substituent groups, other than hydrogen, that complete the molecular structure.

Here is a simple list of rules to follow. Some examples are given at the end of the list.

  1. Firstly, the longest chain is to be identified which is known as parent chain
  2. Identification of all substituents groups is to be done
  3. Number the carbons of the parent chain from the end that gives the substituents the lowest numbers. When comparing 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.
  4. If the same appending group occurs more than once, the location of each point on which the appendix group is given. Repetition of an appending group makes prefix occur di, tri, tetra etc.
  5. If there are two or more different appending groups then, alphabetical order is used to enlist them. The prefix used for the appending group in alphabetical order is iso. The prefixes secondary and tertiary are used when compared.
  6. If chain of equal length is to be made parent chain, then, following points aka priority:

The greatest number of side chains.
Substituents having the lowest- numbers.
Having the greatest number of carbon atoms in the smaller side chain.
Having least branched side chains

7. The prefix cyclo is directly used for cyclic hydrocarbons.

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.

CH4 → methane

C2H6 → Ethane

CH3 —CH3 → Ethane

C3H8 → Propane

CH3 —CH2 —CH3 → n-propane

CH3 —CH2 — CH2 —CH2— CH3 → n-pentane

2-methyl pentane
source:http://www.kentchemistry.com
Fig:2-methyl pentane

2

→ Isohexane OR 2 – methyl pentane (IUPAC)

2-methyl propane
source:http://vignette1.wikia.nocookie.net
Fig:2-methyl propane

→ Isobutane OR 2 − methyl propane

IUPAC Nomenclature

Prefix + word root + primary suffix + secondary suffix

3-methyl hexane
source:http://www.kentchemistry.com
Fig:3-methyl hexane

Prefix → 3-methyl

Word root → Hex

Primary suffix → ane

Therefore the IUPAC name is 3-methyl hexane

2,2-dimethyl propane
source:http://www.chemstone.net/
Fig:2,2-dimethyl propane

Prefix → 2,2 – dimethyl

Word root → prop

Primary suffix → ane

3,6,6_trimethyl-5,5-diethyl
source:http://images.tutorvista.com
Fig:3,6,6_trimethyl-5,5-diethyl nonane

Prefix →3,6,6_trimethyl-5,5-diethyl-4-propyl

Word root → Non

Primary suffix → ane

The IUPAC name is3,6,6_trimethyl-5,5-diethyl-4-propyl-nonane.

Prefix

-CH3 → Methyl

-C2H5 → Ethyl

-Cl → Chloro

-Br → Bromo

-I → Iodo

-F → Fluoro

-CO → Keto

-CHO → Aldo

-NH2 → Amino

-OH → Hydroxyl

-CN → Cyano

-NO2 → Nitro

CH3 Br Cl

I I I

CH3 — C— C— C— CH2— CH3

I I I

Cl I Cl

Prefix → 3-bromo 2, 4, 4 –trichloro 3-iodo 2-methyl

Word root → Hex

Primary suffix → ane

The IUPAC name is 3-bromo 2, 4, 4 –trichloro 3-iodo 2-methyl hexane.

Note:

R-X → alkyl halide or haloalkane

X = Cl, Br, I, F

CH3-Cl

Chloromethane OR Methyl Chloride

CH3-CH2-CH2-Br

Bromo Propane OR Propyl bromide

Prefix → 3 – bromo 2 – chloro 3, 4 – diethyl 4 – methyl 2 – nitro

Word root → Hept

Primary suffix → ane

The IUPAC name is 3 – bromo 2 – chloro 3, 4 – diethyl 4 – methyl 2 – nitro Heptane

Prefix → 3, 3, 7 – tribromo 2, 2 – dichloro 4,4 – diethyl 6 – iodo

Word root → oct

Primary suffix → ane

The IUPAC name is 3, 3, 7 – tribromo 2, 2 – dichloro 4,4 – diethyl 6 – iodo Octane

Isomerism

The organic compounds having same molecular formula but different structural formula are called isomers and the phenomenon is called isomerism.

From butane isomers, occur i.e. methane, ethane, propane does not have isomers.

E.g. Butane (C4H10)

CH3 – CH2 – CH2 – CH3 → n – butane

CH3 – CH – CH3 → 2 – methylpropane

I

CH3

E.g. Pentane (C5H12)

source:http://www6.miami.edu/ fig:isomers of pentane
source:http://www6.miami.edu
fig:isomers of pentane

E.g. Hexane (C6H14)

source:www.meritnation.com fig:isomers of hexane
source:www.meritnation.com
fig:isomers of hexane

E.g. Heptane(C7H16)

sorce:http://s3.mnimgs.com/ fig:isomers of heptane
source:http://s3.mnimgs.com/
fig:isomers of heptane

Reference:

Pulse, Tracy. Introduction to chemistry. u.s.a: flexbook, 2010.

Pathak, Sita Karki. The Text Book of Chemistry. Kathmandu: Vidhyarthi Pustak Bhandar, 2012.



  • Identify the longest carbon chain. This chain is called the parent chain.
  • 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 comparing 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.
b) the chain whose substituents have the lowest- numbers.
c) the chain having the greatest number of carbon atoms in the smaller side chain.
d)the chain having the least branched side chains.

  • A cyclic (ring) hydrocarbon is designated by the prefix cyclo- which appears directly in front of the base name.
.

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Balkrishna pokharel liverpool sushil.pokharel.7528@gmail.com

Do this nomenclature ch3ch=chch2c=-cch3


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But-2-ene-1,4-dial

Structure of this IUPAC name


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