Comprehension # 3
Branched - chain alkanes are named according to the following rules.
(1) Longest chain Rule - Locate the longest continuous chain of carbon atoms. This chain determines the parent name of the alkane.
(2) Lowest set of locants -The longest continuous chain are numbered by arabic numerals 1,2,3,4....from one end of chain to the other, in such a manner that carbon atom carrying first substituent gets the lowest number.
(3) Name of the branched chain alkane - The substituent name and the parent alkane are joined in one word and there is a hyphen between the number and the substituent name.
(4) Alphabetical order of the side chains- When two or more substituent group should be listed alphabetically.
(5) Numbering of different alkyl groups at equivalent positions - If two different alkyl groups are present at equivalent positions the numbering of the parent chain is done in such a way that alkyl group which comes first in the alphabetical order gets the lower number.
(6) Naming of same alkyl groups at different positions - When two or more substituents are identical, indicate this by the use of prefixes di, tri, tetra and soon. Commas are used to separate number from each other.
(7) Rule of larger number of subsitiuents - If a compound has two or more chains of the same length, the parent hydrocarbon is the chain with the greater number of substituents.
(8) Numbering the complex substituent - Name such as iso-propyl, sec-butyl and tert-butyl are acceptable substituent name is the IUPAC system of nomenclature but systematic name are preferable. Systematic substituent names are obtained by numbering the substituent starting at the carbon that is attached to the parent hydrocarbon. This means that the carbon that is attached to the parent hydrocarbon is always the number-1 carbon of the substituent. In following compound `CH_(3)-CH_(2)-underset(CH_(3))underset(|)overset(CH_(3))overset(|)(C)-underset(CH_(3))underset(|)(CH)-overset(CH_(3))overset(|)(CH)-CH_(2)-CH_(3)`
THe correct IUPAC name of the following compound is -
`CH_(3)-CH_(2)-CH_(2)-underset(CH_(3))underset(|)underset(CH-CH_(3))underset(|)(CH)-CH_(2)-CH_(2)-underset(CH_(3))underset(|)(CH)-CH_(3)`
A. 2-Methyl-5-isopropyloctane
B. 2,6-Dimethyl-5-propylheptane
C. 5-isopropyl-2-Methylocatane
D. 4-(1-Methylethyl)-7-methylocatane
