Naming Substituents and Carbon Pair

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Crystal Escobar 1F
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Joined: Fri Sep 25, 2015 3:00 am

Naming Substituents and Carbon Pair

Postby Crystal Escobar 1F » Wed Feb 24, 2016 5:14 pm

When naming a hydrocarbon, do the numbers that represent what carbon the substituent is bonded to always start with the least carbon and the first named substituent or is it only when the substituent numbers are the same?
Hope I make sense!

704564167
Posts: 20
Joined: Fri Sep 25, 2015 3:00 am

Re: Naming Substituents and Carbon Pair

Postby 704564167 » Wed Feb 24, 2016 11:14 pm

When figuring out which number carbon a substituent is bonded to, you always count so that it will be the lowest number carbon. If there are more than one substituents, the same rule still applies.

If you are deciding between, for example, 3, 6, 7 and 2, 6, 9 you would not add them up and see which one has the smallest sum (3+6+7=16 and 2+6+9=17). This would cause you to choose the 3, 6, 7 numbering but you actually need to choose the 2, 6, 9 numbering since 2<3.

If the substituent numbers are the same (like 3, 5 and 5, 3), then you give the substituent that comes first in alphabetical order the lower number and the other substituent the other number. Hope this helps!


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