Chemical Forums

Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: lord farquaad on October 01, 2021, 01:15:24 PM

Title: Why does this methylpropyl start with 1 if it is located on the third carbon?
Post by: lord farquaad on October 01, 2021, 01:15:24 PM

(see attached image)

Title: Re: Why does this methylpropyl start with 1 if it is located on the third carbon?
Post by: Babcock_Hall on October 01, 2021, 01:25:35 PM

If you just saw the words "1-methylproply" without reference to any particular structure, what would it mean to you?
EDT
Have you studied complex (branched) substituents in nomenclature?

Title: Re: Why does this methylpropyl start with 1 if it is located on the third carbon?
Post by: lord farquaad on October 01, 2021, 09:05:26 PM

It would mean that there is a methylpropyl group on the first carbon (I thought). And I am not sure... I am in organic chemistry I. We just finished naming and moved to stereochemistry. Unless branched substituents include those like secbutyl, tertbutyl and so on. Also, if you have a chair conformation of a cyclohexane and had to evaluate which conformation is most stable, how would you decide between tertbutyl and secbutyl which was the bulkier substituent? Are they equal due to having the same number of carbons or is there a difference based on their geometry?

Title: Re: Why does this methylpropyl start with 1 if it is located on the third carbon?
Post by: Babcock_Hall on October 02, 2021, 11:35:16 AM

Regarding your first question, branched substituents can be named formally or informally.  For example, the 1-methylethyl group is another name for the isopropyl.  The numbers are assigned moving away from the branch point.

Regarding your second question, look at a table of axial strain energies for methyl, ethyl, isopropyl, and tert-butyl.  There is a big jump between the last two.  Draw them or make a model, and you can easily see why.