[qw098]

Hi,

I have the HMBC of Ipsenol shown below. I can't seem to understand why I get these cross-peaks that don't correspond with my signals. The peaks I am talking about are labelled with an arrow in my HMBC shown below.

If someone can explain why I get those cross-peaks shown by my arrow below it would be much appreciated.

Thanks!

[discodermolide]

Are they not ¹³C side bands?

[qw098]

Hmmm what exactly are 13C side bands

I googled it but didn't come up with anything clearly explaing it.

[discodermolide]

Hmmm what exactly are 13C side bands

I googled it but didn't come up with anything clearly explaing it.

A quote from Wikipedia

"Carbon satellites are small peaks that can be seen shouldering the main peaks in an NMR spectrum. These peaks can occur in the NMR spectrum of any NMR active atom (e.g. 19F or 31P NMR) where those atoms adjoin a carbon atom (and where the spectrum is not 13C-decoupled, which is usually the case). However, Carbon satellites are most often encountered in proton NMR.
In the example of proton NMR, these peaks are not the result of proton-proton coupling, but result from the coupling of 1H atoms to an adjoining 13C atom. These small peaks are known as carbon satellites as they are small and appear around the main 1H peak i.e. satellite (around) to them. Carbon satellites are small because 13C only makes up about 1% of the atomic carbon content of carbon, the rest of the carbon atoms are predominantly NMR inactive 12C. Carbon satellites always appear as an evenly spaced pair around the main 1H peak. This is because they are the result of 1% of the 1H atoms coupling to an adjoined 13C atom to give a wide doublet (13C has a spin of a half). Note, if the main 1H-peak has proton-proton coupling, then each satellite will be a miniature version of the main peak and will also show this 1H-coupling, e.g. if the main 1H-peak is a doublet, then the carbon satellites will appear as miniature doublets, i.e. one doublet on either side of the main 1H-peak."

They may be spinning side bands, if this is the case try reducing the spinning speed.  I can't tell from your example.

[Babcock_Hall]

How large is the separation between the two peaks on either side of the main peak?  You have to calculate this in Hz from the ppm difference.  If it matches a typical one-bond CH coupling constant in value, then I think the explanation based on satellites is sound.

[qw098]

Yes, you are right Babcock. I asked the NMR expert at my school the other day and he indeed said they were just one-bond CH coupling that leaked on to the HMBC