while naming cyclic compounds from where should we start numbering? give eg''s

When naming cyclic compounds, first determine if the ring is the parent, or not.

If the ring has more carbons than any of the alkyl groups attached, the ring is the parent. If not, the ring becomes a cycloalkyl group and is a prefix for the main chain.

 

1) In this example, the ring has four carbons and the chain has eight. 

The chain is the parent and the ring is a prefix. The ring is a cyclobutyl group on #1.

The compound is named as 1-cyclobutyloctane.

 

2) In this example, the ring has five carbons and the alkyl group has three.

The five-carbon ring is the parent and is called cyclopentane.

The one alkyl group will be on #1.The compound name is Propylcyclopentane.

 

3) When a ring has multiple groups, the rule for numbering is: “Number around the ring so as to arrive at the lowest possible sum of the position numbers”.

The sum in this molecule is 1 + 3 = 4.

In the below compound Lowest possible sum 1 + 2 + 4 = 7

 

4) If you have two possibilities for lowest possible sum, and only then you should alphabetize to prioritize your groups.

Two possible lowest sums of 4, where the groups must be on carbons #1 and #3. 

Prioritize by alphabetizing – the ethyl will be #1 and the isopropyl will be #3.

The name of the compound is 1-ethyl-3-isopropylcyclopentane.

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in a cyclic compound give least position to double or tripple bonds, side groups etc. and number accordingly.

if its just a skeleton, you can number from anywhere any direction. but if u attach something or make a double or triple bond, you should number in such a way that it the bond or a molecule attached to the chain gets least counting possible.

plz view this pic imade just now :http://imgur.com/8C8PCpC

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