Don’t Be Futyl, Learn The Butyls

by James

in Nomenclature

Nomenclature: what a headache. We’ve got all these accumulated years of jargon regarding chemical structures, and unless you learn the lingo, it can be confusing to follow what’s going on.

Case in point: butyl. There are FOUR different types of “butyls”, and they all have their own name. In addition they each have a common name (“trivial name”) which they commonly go by.  It’s easy to get confused. So today’s post is a guide to sorting them out.

Butane has four carbons. Now there’s two potential ways to organize those carbons – the 4-carbon straight chain (n-butane), and the 3-carbon chain with a methyl group on carbon #2 (2-methyl propane, also known as “isobutane”).  Don’t believe me? Try it out for yourself. There’s only two ways to do it.

Now let’s say we have some substituent. For example, let’s make it OH. Let’s remove a hydrogen from butane and replace it with OH. If you look at n-butane, you’ll see there’s really only two ways to do it. You can take it from C-1 (or C-4), in which case you get a primary alcohol (1-butanol, or “n-butanol”). Or you can take it from C-2 (or C-3) in which case you get a secondary alcohol (2-butanol, or “sec-butanol”). We sometimes shorten that to “s-butanol”.

Likewise for the isobutyl skeleton there is two ways to do it. You can replace an H on C-1 (or C-3 or C-4) with OH, in which case you get 2-methyl-1-propanol (“isobutanol”).  Or you can replace an H on C-2 with OH, and get 2-methyl-2-propanol (“t-butanol”). Those are the only two ways to do it!

This applies to other groups too. So if we used Cl instead of OH, we’d have n-butyl chloride, s-butyl chloride, t-butyl chloride, and isobutyl chloride. And if we used some other group, those four names – n-butyl, s-butyl, t-butyl or isobutyl – all remain the same.

 So here’s the punch line for butyl.

  1. 1-butyl (“n-butyl” where “n” stands for “normal”)
  2. 2-butyl (“s-butyl” where “s” stands for “secondary”)
  3. 2-methyl-1-propyl (“isobutyl”)
  4. 2-methyl-2-propyl (“t-butyl”)
What about pentyl? Thankfully, there’s too many possibilities to be limited to this simple system. There’s only one weird case: 2,2-dimethylpropane. We call this “neopentane”. If you replace an H with a substituent, that becomes the “neopentyl” group.

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{ 18 comments… read them below or add one }

nkululo gugu February 8, 2013 at 3:08 pm

thank you very much with your great work, we need more people like you who inspire students to try and do best….can i please get soft copy of your organic 2 notes.

thank you.

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Missgigglyy June 5, 2013 at 6:14 pm

Thank you so much. :) Helped ALOT :D

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Smawar Mand August 19, 2013 at 3:47 pm

I have a quesion! Are isobutyl alcohal and t butyl alcohal postition isomers or chain isomers?

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James Ashenhurst August 20, 2013 at 2:52 pm

Constitutional isomers. The terms “positional” and “chain” isomers are not familiar to me, but if I interpret their use correctly they are position isomers.

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A. Khan October 4, 2013 at 10:23 pm

Very helpful. Read the section in my text several times, couldn’t figure out the difference between secondary and iso forms. Read your explanation once. Got it.

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James Ashenhurst October 9, 2013 at 9:33 am

Great, glad you found it helpful!

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josh January 22, 2014 at 9:26 pm

1-butylchloride should actually be called 1-chlorobutane (http://en.wikipedia.org/wiki/1-Chlorobutane)

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helpinghere April 9, 2014 at 8:18 am

1-butylchloride — Common naming
1-chlorobutane —IUPAC naming
…….this is just how the chemistry nomenclature is….a littale confusing (^.^)~

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Jesse March 3, 2014 at 6:07 pm

At the end where you go from Neopentane to Neopentyl Alcohol would the formula change to 2,2-dimethylpropanol because you added the OH?

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James March 9, 2014 at 8:51 pm

Yes it would!

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saira March 31, 2014 at 9:17 pm

Keep Up the Excellent Work! Its great to see individuals, such as yourself, helping students in need.

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Saba April 3, 2014 at 11:58 pm

This was so helpful!
Can this apply to different carbon chains that are greater than butane?
For example is it possible to have a tert-hexanol or isoheptane?

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James April 15, 2014 at 10:20 am

Hi – no, it only applies to butane. There are so many isomers possible for chains higher than 4 that the prefixes “tert”, “iso” and so on would not refer to unique isomers.

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Amitrajit Chattopadhyay June 15, 2014 at 3:50 pm

what should be the IUPAC nomenclature for t-Butyl group? In Wikipedia it is given as 1,1-dimethylethyl.I am confused

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VAMSI June 17, 2014 at 12:03 am

Thank you so much. :) Helped ALOT :D

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Abhinav June 19, 2014 at 4:06 am

This section was really helpful.. But can you assure me that these terms (sec,neo,tert,iso) will not comes for others except butane.??As in your section you were specific about butane.. You were not general

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James June 26, 2014 at 5:18 pm

sec, tert, only apply to butane. iso applies to butyl and propyl. neo only applies to pentane.

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Jessica S. June 26, 2014 at 10:24 am

Best find ever! Love the whole website.

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