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Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: pallidol on August 25, 2015, 02:43:58 AM

Title: missing peak of carbon NMR
Post by: pallidol on August 25, 2015, 02:43:58 AM: dear guys.

I need confirmation regarding my compound structure. One of the carbon peak for the compound is missing. The missing peak is the quaternary carbon sharing two chloro groups . Is it being suppressed due to the presence of the chloro group?

I am little bit confused. Anyway thanks beforehand.
Title: Re: missing peak of carbon NMR
Post by: clarkstill on August 25, 2015, 02:45:46 AM: What is the structure? Can you post complete spectra?
Title: Re: missing peak of carbon NMR
Post by: pallidol on August 25, 2015, 02:58:46 AM: here is the structure.
Title: Re: missing peak of carbon NMR
Post by: Dan on August 25, 2015, 04:52:48 AM: Can you post the complete 13C spectrum?
Title: Re: missing peak of carbon NMR
Post by: pallidol on August 25, 2015, 05:25:39 AM: guys i am really sorry for the mistake i have made during the uploading of the spectrums. Here i reattached the spectrums. you may take a look at it again.
Title: Re: missing peak of carbon NMR
Post by: ATMyller on August 25, 2015, 05:43:51 AM: Are you sure the spectra is wide enough. Just one neighboring chloro and one ketone group can give chemical shift as far as 195 ppm downfield, Then again dichloroacetaldehyde has it around 68 ppm.

Or it just comes out short due to too small D1 time.
Title: Re: missing peak of carbon NMR
Post by: Irlanur on August 25, 2015, 10:33:50 AM: My first guess would be that the repetition time is too short. the quaternary C will most likely have quite a long T1, so you will more or less supress it.
Title: Re: missing peak of carbon NMR
Post by: Babcock_Hall on August 25, 2015, 02:24:47 PM: The typical quaternary carbon also may experience a weaker heteronuclear NOE.
Title: Re: missing peak of carbon NMR
Post by: pallidol on August 26, 2015, 03:09:22 AM: Quote from: ATMyller on August 25, 2015, 05:43:51 AM
Are you sure the spectra is wide enough. Just one neighboring chloro and one ketone group can give chemical shift as far as 195 ppm downfield, Then again dichloroacetaldehyde has it around 68 ppm.

Or it just comes out short due to too small D1 time.

yes the width is enough to show overall peaks that appear.
Title: Re: missing peak of carbon NMR
Post by: pallidol on August 26, 2015, 05:06:30 AM: Quote from: Irlanur on August 25, 2015, 10:33:50 AM
My first guess would be that the repetition time is too short. the quaternary C will most likely have quite a long T1, so you will more or less supress it.

So that means i need to increase the resolution of my carbon scan?
Title: Re: missing peak of carbon NMR
Post by: Irlanur on August 29, 2015, 07:50:51 PM: no, the resolution is not the problem. If what I mentioned is indeed the problem, you should wait longer between the scans.