1,2-ethanediol Proton Splitting
Started by letaps
The NMR spectrum should only have a triplet and a singlet. The hydrogen on the alcohol, is a bit too far away (it's 4 atoms away) to be split by the hydrogen on the carbon.
Side note: Any long range coupling that might occur should be too small to see anyway, and I don't think that's on the MCAT.
Side note: Any long range coupling that might occur should be too small to see anyway, and I don't think that's on the MCAT.
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It would be a triplet (due to the hydrogens attached to the carbon) and a singlet (due to the hydrogen on the OH group). Under usual conditions, an OH proton does not split the NMR signal of adjacent protons. Also, the signal due to an OH proton is not split by adjacent protons. So it would be a triplet and a singlet not triplet and doublet.
The two protons on the alcohol are in the same chemical environment, therefore its a singlet.
But aren't the hydrogens on the carbons in the same chemical environment as well? Why are they splitting eachother? because they aren't splitting the alcohol proton.
But aren't the hydrogens on the carbons in the same chemical environment as well? Why are they splitting eachother? because they aren't splitting the alcohol proton.
Right, but what is splitting those chemically equivalent protons on the carbons? There are 4 chemically eq on the carbons, and the two on the OH. And they aren't splitting the OH proton right? I'm really having a brain freeze I'm usually fine with NMR.
Why isn't it singlet for the two hydrogens on the OH, singlet for all the rest of the hydrogens on the carbon, because they are chem equivalent and there's nothing left to split them.
Why isn't it singlet for the two hydrogens on the OH, singlet for all the rest of the hydrogens on the carbon, because they are chem equivalent and there's nothing left to split them.
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They don't split the OH proton-nothing really splits the OH protons in NMR because (from what I remember anyway) the proton undergoes rapid exchange. It doesn't really stay on the oxygen too long for the NMR to detect splitting/coupling.
So where is the triplet coming from..where are 2 extra protons that are splitting the 4 hydrogens on the carbons?
There are 6 hydrogens total yes? 2 are the OH protons. They aren't split and do not split. Therefore there are 4 hydrogens left. All 4 of those hydrogens are chemically equivalent.
SO
shouldn't there be a singlet for the OH protons, singlet for the 4 hydrogens on the carbons?
There are 6 hydrogens total yes? 2 are the OH protons. They aren't split and do not split. Therefore there are 4 hydrogens left. All 4 of those hydrogens are chemically equivalent.
SO
shouldn't there be a singlet for the OH protons, singlet for the 4 hydrogens on the carbons?
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Yes, there is a singlet for the OH protons, and no there is not a singlet for the 4 hydrogens. Just because there are chemically equivalent hydrogens doesn't mean that they do not split each other-it just means that there will be one signal representing them all-I think that's what's causing the confusion. So we already established that the OH hydrogen does not split, and so there is 1 signal represenitng BOTH OH hydrogens. There are two -CH2-groups, each splitting the other (2 H + 1=3), hence the triplet. Since there are two chemically equivalent -CH2- groups, there will be ONE signal representing them both (just like how there's 1 signal representing BOTH OH protons)-the only difference is the methylene hydrogens split each other. Don't confuse chemical equivalency with splitting.
There's a mirror plane that I've depicted with a blue dotted line. The two red hydrogens are equivalent as are the green ones (they both have the same respective environments). The Red Hydrogens are split by the two green ones (2 H nearby + 1 =3), and vice versa. But since there's a plane of symmetry, they will have the same chemical shift so it will appear to be one big triplet of 4 H's. The alcohol hydrogen is too far away to be split, and will be a singlet (0 H + 1= 1). And since there is an axis of symmetry the other alcohol hydrogen has the same chemical shift.
Consider an isopropyl group as another example: CH3-CH-CH3 (obviously it's not linear-it's sort of a v shaped molecule). So, a septet and doublet are characteristic of an isopropyl group. The hydrogens on the two methyl groups are chemically equivalent, and so they both split the hydrogen on the CH group (1+1=2, there's your doublet)-you'll only see ONE doublet to represent BOTH methyl groups. They are chemically equivalent, yes, but there's still splitting. The CH will split both methyl groups (6+1=7, there's your septet).
I don't think you're right here. You only split when there isn't chemical equivalence. Chemically equivalent protons do not split. For example, here's the spectrum for 1,2-dichloroethane. There's no coupling.
http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi
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2 singlets. One with integration 2, one with integration 1.
The methylene protons are chemically equivalent and thus don't split each other.
No, pentane has a triplet for the terminal carbons, a sextet for the second carbons in, and a quintet for the middle carbon.
http://www.muhlenberg.edu/depts/chemistry/chem201woh/1Hpentane.html
Butane: a quartet and a triplet
The quartet is from CH2 being split by the terminal CH3
The triplet is from CH3 being split by CH2.
The CH2s don't split each other because they're equivalent.
They're messy, but I'm pretty positive that's a quartet and a triplet
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No. I didn't say anything close to that? You don't double the triplet and sextet for pentane because they're equivalent carbons. AndI'm not sure where you got 2 singlets for butane from anything I said OR the spectrum I posted.
And here is butane: http://www.muhlenberg.edu/depts/chemistry/chem201woh/1Hbutane.html
And here is butane: http://www.muhlenberg.edu/depts/chemistry/chem201woh/1Hbutane.html
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>.< Stop spoilin mah ay ay em seez!
Seriously, can we ban this guy? capn is right, he has made a dozen other threads, after repeatedly being told not to.
