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Class 10, Science, Chapter-4, Lecture-3, IUPAC Nomenclature of Hydrocarbons-Part-1 (Notes)

Two systems of Nomenclature:

1. Trivial system (common names)

2. IUPAC system (IUPAC names) [IUPAC = INTERNATIONAL UNION OF PURE AND APPLIED CHEMISTRY]

A. IUPAC System of Naming for Straight Chain:

A-1. Saturated Hydrocarbons

STEM (Word Root)

Suffix
Used

Number of Carbon atoms

Stem used

1

meth

ane

2

eth

3

prop

4

but

5

pent

6

hex

 7

hept

 8

oct

 9

non

10

dec

A-2. Unsaturate Hydrocarbons.

(a) up to 3 carbon atoms

Word-root + ene/yne

(b) for more than 3 carbon atoms

Number the carbon atoms so that the multiple bond gets the Lowest position number (Locant)

Word-root + Hyphen + Locant + ene/yne

B) IUPAC System of Naming for Branched-chain

B-1. Saturated Hydrocarbons

Case: I – Only One Alkyl Group is Present:

(i) Search for the longest chain (parent chain)

  • must be continuous
  • may not be straight

(ii) Number the carbon atoms so that the BRANCH gets LOWEST Position Number

(iii) Search the ALKYL GROUP.

(iv)

Locant + Hyphen + alkyl group + parent alkane

Case: II – Repeated Same Alkyl Groups are Present:

(i) Search for the longest chain (parent chain)

(ii) Number the carbon atom so that the locant of the first branch is MINIMUM (Locant is minimum at the first point of difference)

(iii) Search for the ALKYL GROUPS present.

(iv)

Locant + comma + Locant + comma . . . (n-time) + Hyphen + di/tri/tetra . . . + alkyl group + parent alkane