It's been a good few years since I had chemistry and at a lower level than what I need for this, so I'm hoping jsp can give me some insight.

I am having troubles understanding the names of the functional groups in valine, leucine and isoleucine


My trouble is with the names given to the functional groups: propyl, butyl and isobutyl. For propyl, since the attachment is at a secondary carbon, I feel it would be more appropriate to address this as sec-propyl. For me, propyl would suggest that one of the terminal carbons is used. I realize that systematically this means the chain grows longer but since we're only naming the functional groups it shouldn't be a problem?

Likewise, for Leucine, I come to understand that a Butyl group is nothing more than R-CH2-CH2-CH2-CH3 (https://en.wikipedia.org/wiki/Butyl_group); here, one of the non-terminal carbons branches outwards. I feel that this should be called isobutyl: the upper CH2 can be considered a terminal carbon group. What I call isobutyl, apparently is just a butyl group.

Then, for isoleucine, the butyl carbon that is attached to the backbone is a secondary and not a terminal carbon. I feel that this would then be called sec-butyl.


According to the image provided to us by the professor, I am wrong on all counts: the first one is simply propyl, the second one that I believe to be isobutyl is regular butyl and the last one, which I think should be sec-butyl becomes isobutyl. If I'm not mistaken, the image comes from the book Becker's World of the Cell.

I used to fap during O chem

aggre

Nobody with knowledge in chemistry? :/

forgive the shoddy attempt at hand-drawing these in paint on a laptop



the naming convention in organic chemistry for alkyl side chains is based on what degree is the carbon connected to the parent chain (ex: sec-butyl is a secondary carbon, tert-butyl is a tertiary carbon)

again, this is for organic chemistry. biochemists don't follow that logical naming convention

edit: messed up my isobutyl drawing. isobutyl should have a fork and form what appears to be 2-methylpropane with an r group attached to the methyl (if that makes sense)

This post was edited by Zpot on Oct 6 2017 01:29am

To reply to your edit, any terminal C atom will meet that criterium lol. But thanks. Happy to know I'm not insane but biochemists are just whacky like that.
Who knows, I might become one ._.

the way i drew sec-butyl above is what biochemists consider isobutyl

Yes, that's my problem exactly haha