Easy BR Ochem NMR question

[slz1900]

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BR says that 2-chloropentane would NOT show a 2H quartet, but there are two hydrogens on the third carbon and they are adjacent to 1 hydrogen on the second carbon and 2 on the fourth carbon, so wouldn't that result in a 2H quartet?

According to BR a 2H quartet would only form when you have an isolated CH2 next to a CH3, but I don't understand why the hydrogens that are splitting the 2H all have to be on the same carbon.

 

[PlumbLine]

BR says that 2-chloropentane would NOT show a 2H quartet, but there are two hydrogens on the third carbon and they are adjacent to 1 hydrogen on the second carbon and 2 on the fourth carbon, so wouldn't that result in a 2H quartet?

According to BR a 2H quartet would only form when you have an isolated CH2 next to a CH3, but I don't understand why the hydrogens that are splitting the 2H all have to be on the same carbon.

For splitting, they don't have to be on the same carbon, but they have to be "equivalent" hydrogens. In your example the hydrogen bonded to the carbon that's bonded to chlorine is experiencing a far different interaction with carbon than the 2 hydrogens on the 4th carbon. Therefore instead of a 2H quartet you would see a 2H doublet triplet. One splitting from the adjacent single hydrogen and then another splitting from the adjacent 2 hydrogens.

If you think about it that way, BR is correct that you can't get a quartet without an isolated CH2 next to CH3. I'm trying to think of a different situation where that's possible and I'll post it if I can come up with one. Hope that helps!

 

[slz1900]

For splitting, they don't have to be on the same carbon, but they have to be "equivalent" hydrogens. In your example the hydrogen bonded to the carbon that's bonded to chlorine is experiencing a far different interaction with carbon than the 2 hydrogens on the 4th carbon. Therefore instead of a 2H quartet you would see a 2H doublet triplet. One splitting from the adjacent single hydrogen and then another splitting from the adjacent 2 hydrogens.

If you think about it that way, BR is correct that you can't get a quartet without an isolated CH2 next to CH3. I'm trying to think of a different situation where that's possible and I'll post it if I can come up with one. Hope that helps!

Thank you! Yes that helps. So what would a doublet triplet look like on a spectrum? Would each peak of the doublet be split 3 times or would each peak of a triplet be split 2 times, or something else?

 

[PlumbLine]

You would see 6 peaks. Here is a good example: http://www.chem.ucla.edu/harding/IGOC/D/doublet_of_triplets.html

 

[slz1900]

You would see 6 peaks. Here is a good example: http://www.chem.ucla.edu/harding/IGOC/D/doublet_of_triplets.html

Cool, thanks.

 

[gabdolce]

Always a good resource for example NMRs:

http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi

 

[slz1900]

Always a good resource for example NMRs:

http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi

Thanks. I was looking for more practice