91Ó°ÊÓ

Cis configuration is when two groups are on the same face of the ring and trans configuration is when the groups are on opposite faces.Both isomers are stable and neither can be converted into the other without breaking and reforming chemical bonds.

Count the number of carbon atoms in the ring and the number in the largest substituent whichever has highest carbon atom will be considered as parent. If the number of carbon atoms in the ring is equal to the number in the substituent in that case ring is taken as parent.

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For an alkyl- or halo-substituted cycloalkane, choose a point of attachment as carbon 1 and number the substituents on the ring so that the secondsubstituent has as low a number as possible. Same procedure for third or fourth substituent so has low number as much as possible, until a point of difference is found.

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a.

• The ring has 5 carbon atoms.
• One methyl group and one ethyl group is present..
• Hence, the name of the compound is $1−Ethyl−3−methylcyclopentane$

b.

• The ring has 6 carbon atoms.
• Three methyl group are present.
• Hence, the name of the compound is