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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Dillema103 on February 28, 2019, 11:21:09 PM

Title: Impossible task?
Post by: Dillema103 on February 28, 2019, 11:21:09 PM

I have a task in which I need to draw a structural formula of 5-ethyl-hexane but I am not sure if that is possible as adding ethyl to the 5th carbon would add 2 additional ones making it a heptane. Does an alkyl not count towards the carbon chain making this possible as CH3CH2CH2CH2CH(CH2CH3)CH3, if not am I correct in assuming that it is not possible to complete this task?

Title: Re: Impossible task?
Post by: AWK on March 01, 2019, 02:15:03 AM

According to nomenclature rules, only one ethyl-hexane exists - namely 3-ethyl-hexane.
Even for monosubstituted ethyl-heptanes, only locants 3- or 4- are possible (Rule: The locants are assigned such that the principal functional group gets the lowest possible locant).

Title: Re: Impossible task?
Post by: Dillema103 on March 02, 2019, 10:06:25 AM

Quote from: AWK on March 01, 2019, 02:15:03 AM

According to nomenclature rules, only one ethyl-hexane exists - namely 3-ethyl-hexane.
Even for monosubstituted ethyl-heptanes, only locants 3- or 4- are possible (Rule: The locants are assigned such that the principal functional group gets the lowest possible locant).

Thanks for the answer. What would happen in a case where locants 2- 3- and 4- were all occupied? Would the ethyl go on the 5th locant then?

Title: Re: Impossible task?
Post by: AWK on March 02, 2019, 11:08:58 AM

The first branch of carbon chain should have the lower locant - 2,4-dimethyl hexane (not 3,5-...), 3-ethyl-2,4-dimethyl hexane, 3-ethyl-2,5-dimethyl hexane, 3-ethyl-2,2,4-trimethyl hexane, 3-ethyl-2,4,5-trimethyl hexane.
4-Ethyl-2,2,3,3-tetramethyl hexane is the correct name.
Search for branched hydrocarbons nomenclature.

Title: Re: Impossible task?
Post by: Dillema103 on March 02, 2019, 12:13:18 PM

Much appreaciated!