-
- admin
- Site Admin
-
- Posts: 647
- Joined: Wed Aug 11, 2004 12:19 am
By Anonymous on Wednesday, June 30, 2004 - 07:39 am:
hi, i know this is a LC forum. But i do have a question aoubt HNMR of HDI(O=C=O=N-CH2-CH2-CH2-CH2-CH2-CH2-N=C=O).The areas of the three different kinds of H are different,about 20% difference. Could anybody tell me why? thank you!
-------------------------------------------------------------------------------------------------------
By Constantin Sychov on Wednesday, June 30, 2004 - 08:39 am:
Its allright. Mmmm.. Overhauser effect, as far as I remember.
-------------------------------------------------------------------------------------------------------
By Alexander on Thursday, July 1, 2004 - 06:17 pm:
N=C=O is an electon acceptor, so the closer your CH2 groups to the substituent, the higher the shift to the low field. The central CH2CH2 must be in the strongest field.
-------------------------------------------------------------------------------------------------------
By Anonymous on Sunday, July 4, 2004 - 08:56 am:
hi,alexander, what i meant by that was not the shift,but the area. say, the areas of the 3 different type of Hs are different,the lowest 4 and the bigget 5.3.The structure is O=C=N-CH2-CH2-CH2-CH2-CH2-CH2-N=C=O,not O=C=O=N-CH2-CH2-CH2-CH2-CH2-CH2-N=C=O£sorry about that!
-------------------------------------------------------------------------------------------------------
By Anonymous on Sunday, July 4, 2004 - 02:03 pm:
what's your solvent and what are the shifts and integrals of all the methylene signals? shame you can't scan the spectrum and attach it..
-------------------------------------------------------------------------------------------------------
By Anonymous on Monday, July 5, 2004 - 03:40 am:
I think you have a lot of overlapping in your spectrum, so differences accumulate. Is the spectrum well phased/integrated? Otherwise the compound is not pure. Check it with a C13 spectrum.
-------------------------------------------------------------------------------------------------------
By Alexander on Wednesday, July 7, 2004 - 06:33 pm:
20% difference in integration maybe normal, depends on the instrument and concentration. Try higher concentration/more scans. This will give you a better integration number. You may also have some overlapping from impurities of partially hydrolyzed compound from the reagent or from moisture during the sample prep.
hi, i know this is a LC forum. But i do have a question aoubt HNMR of HDI(O=C=O=N-CH2-CH2-CH2-CH2-CH2-CH2-N=C=O).The areas of the three different kinds of H are different,about 20% difference. Could anybody tell me why? thank you!
-------------------------------------------------------------------------------------------------------
By Constantin Sychov on Wednesday, June 30, 2004 - 08:39 am:
Its allright. Mmmm.. Overhauser effect, as far as I remember.
-------------------------------------------------------------------------------------------------------
By Alexander on Thursday, July 1, 2004 - 06:17 pm:
N=C=O is an electon acceptor, so the closer your CH2 groups to the substituent, the higher the shift to the low field. The central CH2CH2 must be in the strongest field.
-------------------------------------------------------------------------------------------------------
By Anonymous on Sunday, July 4, 2004 - 08:56 am:
hi,alexander, what i meant by that was not the shift,but the area. say, the areas of the 3 different type of Hs are different,the lowest 4 and the bigget 5.3.The structure is O=C=N-CH2-CH2-CH2-CH2-CH2-CH2-N=C=O,not O=C=O=N-CH2-CH2-CH2-CH2-CH2-CH2-N=C=O£sorry about that!
-------------------------------------------------------------------------------------------------------
By Anonymous on Sunday, July 4, 2004 - 02:03 pm:
what's your solvent and what are the shifts and integrals of all the methylene signals? shame you can't scan the spectrum and attach it..
-------------------------------------------------------------------------------------------------------
By Anonymous on Monday, July 5, 2004 - 03:40 am:
I think you have a lot of overlapping in your spectrum, so differences accumulate. Is the spectrum well phased/integrated? Otherwise the compound is not pure. Check it with a C13 spectrum.
-------------------------------------------------------------------------------------------------------
By Alexander on Wednesday, July 7, 2004 - 06:33 pm:
20% difference in integration maybe normal, depends on the instrument and concentration. Try higher concentration/more scans. This will give you a better integration number. You may also have some overlapping from impurities of partially hydrolyzed compound from the reagent or from moisture during the sample prep.
