High resolution 13C NMR spectroscopy. IV—stereochemical assignments in butenedioic acids and 3-pentene-2-ones
✍ Scribed by S. Braun
- Publisher
- John Wiley and Sons
- Year
- 1978
- Tongue
- English
- Weight
- 550 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
Vicinal
-C, H coupling C O M ~~S ,J(CO, H) for butenedioic acids and 'J(CH,, H) for 3-pentene-2-ones have been determined and are correlated with the con6gurathn of the corresponding C=C double bond. For both types the ~W i ~~h i p "J(CH)mns > 'J(CH)cis holds; in the case of the CH,, H couplings, however, the 3J(CH3,H)trcrns values are reduced because of stenc reasons, so that configurational assignments seem possible only when both isomers are present. Additionally, the coupling constants 'J(COCH,,H) and the chemical shifts &-, have been evaluated for the pentenones and it is shown that theseparameters give information about the predominating conformation of a, B-unsaturated methyl ketones.