[orgorox]

Hey guys,

I am trying to figure out the structure from these IR and NMR graphs and I am at a dead end. Please help me find the unknown structure. The Molecular Formula is C15H33N. It's not allowing me to upload all the graphs due to file size so I'll try to explain what I see. The IR only shows C-H sp3 bonds (beyond the fingerprint region). In the proton NMR, it has four total peaks. One at 2.5 that looks like a triplet, one at 1.5 that looks like it has 5 splits, one at 1.3-1.4 and I can't tell the splitting, and one around 1 that's a triplet. The integration is 2:2:4:3, respectively. In the carbon NMR, I see 5 total peaks. One at around 54, one around 30, one around 26, one around 22, and one around 14. In the mass spec, I see 41 m/z at 7 relative abundance, 115 at 21, 170 at 100, 171 at 13, and 227 at 5.

Thanks!

[Babcock_Hall]

It is a forum rule that you must show an attempt before we can help you.  There is a red "Forum Rules" link that you can use to read through them.

[orgorox]

It is a forum rule that you must show an attempt before we can help you.  There is a red "Forum Rules" link that you can use to read through them.

I have been trying to do it for two days. I have had many attempts. It's not letting me post any of the pictures for some reason so I can't show my work.

I know the IHD is 0 so there are no double bonds or rings. I know that there are no N-H bonds so it's a tertiary amine. I know there are 4 types of hydrogens and 5 types of carbons which means there's symmetry. That's all I know and I tried a million molecules but failed. Please help.

[discodermolide]

look in the forum rules under point 3.8, it tells you there how to post pictures.

[orgorox]

look in the forum rules under point 3.8, it tells you there how to post pictures.

Okay now it works. I had to change the properties of it. I removed some of the scribbles to make it more coherent. Again, no hydrogen deficiencies so no double bonds or rings. I know the N will be connected to three carbons with some symmetry. I am completely lost on how to do it. I find it impossible to get the correct integration of hydrogens (2:2:4:3). I need assistance!

[orgorox]

This is what I'm guessing so far but obviously it's wrong. It doesn't give us the splitting for all the Hydrogens... I really need some assistance with this it's frustrating me a lot.

Thanks in advance

[Babcock_Hall]

How much symmetry is in the molecule?

[orgorox]

How much symmetry is in the molecule?

So 15 carbons total in the molecule but only 5 peaks, so all 3 chains are symmetrical?

[Babcock_Hall]

I think that is a very reasonable hypothesis, and now you have a much simpler problem.  You have to propose a structure that is consistent with chemical shifts, with multiplicities, and with integrals.  There is also mass spec data.

[orgorox]

I think that is a very reasonable hypothesis, and now you have a much simpler problem.  You have to propose a structure that is consistent with chemical shifts, with multiplicities, and with integrals.  There is also mass spec data.

The closest thing that I get is just a straight chain of 5 carbons (times 3). However, that doesn't make sense because that assumes carbons 3 and 4 are equivalent when they're obviously not. I have no idea what else to do. I've proposed hundreds of structures that make no sense.

[Babcock_Hall]

I don't understand your most recent comment; I don't see any assumption about the equivalence of C-3 and C-4 built into this proposed structure.  However, I would like to make a guess about the reason your confusion: the simple first-order rules that are initially taught about NMR are misleading in some ways.  Spectra often look very different from the way that they would if these rules were universally true.  Chains of several -CH₂- groups are often quite complex.  One problem is that they are "close coupled" meaning that their difference in chemical shift and their coupling constants are similar in magnitude when measured in Hz.  If I were you, I would try to predict the chemical shifts in the carbon-13 NMR spectrum of your proposed structure and compare with your unknown.

[orgorox]

I don't understand your most recent comment; I don't see any assumption about the equivalence of C-3 and C-4 built into this proposed structure.  However, I would like to make a guess about the reason your confusion: the simple first-order rules that are initially taught about NMR are misleading in some ways.  Spectra often look very different from the way that they would if these rules were universally true.  Chains of several -CH₂- groups are often quite complex.  One problem is that they are "close coupled" meaning that their difference in chemical shift and their coupling constants are similar in magnitude when measured in Hz.  If I were you, I would try to predict the chemical shifts in the carbon-13 NMR spectrum of your proposed structure and compare with your unknown.

I really have no idea how to do this. Could you give me another hint? It was already due but I still would like to know how to do it. Also, when looking at propane, ch3ch2ch3, looking at the hydrogens of the ch2, would they be less or more shielded than the ch3 hydrogens? And why?

Thanks

[Babcock_Hall]

Carbon chemical shift prediction are predicted by the Grant-Paul equation.  There are shift increments for the alpha, beta, and gamma substituents. 
http://www.chem.wisc.edu/areas/reich/chem605/
http://www.chem.ucla.edu/~bacher/General/30BL/NMR/Ccorralkane.html

You can also predict the H-1 NMR chemical shifts by a different set of rules.

[orgopete]

How much symmetry is in the molecule?

So 15 carbons total in the molecule but only 5 peaks, so all 3 chains are symmetrical?

This virtually answers itself. How many ways can you attach five carbons to a nitrogen, and have an integration of 2:2:4:3?