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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: nickname on April 19, 2011, 04:36:03 PM

Title: Determining structure from HNMR (C4H11N)
Post by: nickname on April 19, 2011, 04:36:03 PM

I have to find the structure from the IR spectrum and H NMR for C4H11N

On the IR spect. I see:
N-H stretch at 3309cm-1
alkane (C-H) stretch a little less than 3000cm-1

On H NMR, I see:

triplet at 2.6ppm
multiplet at 1.25ppm
singlet really close to multiplet at 1.2ppm
triplet at 0.8ppm

What molecule could it be?

I think it is
     
                  CH3
                  l
CH3CH2CH2N-H

Is this correct?  Thank you!

Title: Re: Determining structure from HNMR (C4H11N)
Post by: Honclbrif on April 19, 2011, 05:13:37 PM

You see four types of protons in your spectrum, how many types of protons does your proposed structure have?

Also, any integration? Even if its not numeric, wiggly line integration can be worked out with a ruler.

Title: Re: Determining structure from HNMR (C4H11N)
Post by: nickname on April 19, 2011, 05:30:19 PM

Hi!

I thought this was the structure because on my book many times the H attached to nitrogen are not shown on the NMR.

Thanks

Title: Re: Determining structure from HNMR (C4H11N)
Post by: Honclbrif on April 19, 2011, 06:10:47 PM

Do not assume that protons attached to amines do not appear in an NMR spectrum. They usually do appear as singlets, often between 1 and 3 ppm. However, factors such as temperature, concentration, and the ability to hydrogen bond can greatly influence where and how they appear.

Another issue to remain aware of is that peaks from -CH₂- protons in chains can stack up on top of each other into multiplets. You can usually tell when this is happening from the integration.

Also, when you are trying to determine a structure and a formula is provided, the first thing you should always do is calculate the degrees of unsaturation. It will make your life much easier.

Title: Re: Determining structure from HNMR (C4H11N)
Post by: nickname on April 19, 2011, 06:17:06 PM

Hello,

Thank you again for replying.  Yes I calculated the degree of unsaturation and it is equal to 1.  I compared my answers to other isomers with the same molecular formula, but I think this the best one.

What do you think?

Thanks for your help :)

Title: Re: Determining structure from HNMR (C4H11N)
Post by: nickname on April 19, 2011, 07:45:23 PM

I attached the file for the given H NMR and IR.

I think the structure is the one I mentioned before, but I am not sure.

Thanks for your help :)

Title: Re: Determining structure from HNMR (C4H11N)
Post by: Honclbrif on April 19, 2011, 08:23:25 PM

I'd review those structures again

Title: Re: Determining structure from HNMR (C4H11N)
Post by: nickname on April 19, 2011, 08:25:00 PM

hello,

You are saying my answer is wrong right?

Title: Re: Determining structure from HNMR (C4H11N)
Post by: orgopete on April 22, 2011, 07:12:29 PM

Are you sure it is C4H11N?

Title: Re: Determining structure from HNMR (C4H11N)
Post by: Kadabrium on April 23, 2011, 07:10:32 AM

i think it is CH3CH2NHCH2CH3....