Lyaline
30 years after the structure of lyaline was first proposed, a new spectroscopic analysis was performed using state-of-the-art techniques to reveal errors in the original analysis, and eventually, the correct structure.
Iridiod Glycoside
Iridiod Glycoside Clerodendrum (Lamiaceae) is a genus composed of 580 species. It is found in tropical and subtropical regions and mainly includes small trees, shrubs, and herbs. Many members of the genus havebeen used in traditional medicine around the world. C. myricoides is a shrub with bluish flowers that has been used extensively in traditional...
Comatulin A
The analysis of C. rotalaria extracts by UHPLC-MS in conjunction with database searching led to the isolation and structure elucidation of a series of new taurine-conjugated anthraquinones, including Comatulin A, molecular formula C20H19NO10S.
Gelstriamine A
Jin et al studied the novel analgesics used in traditional Chinese medicine and as part of this they isolated and elucidated the structure of a novel triamine monoterpene indole alkaloid, Gelstriamine A, molecular formula C22H27N3O5.
A first pass at detecting an impurity signal in a 1H NMR
I got some great comments from Tony and Gary on the “Dealing with a Mixture…” post that I decided to do a follow-up post. http://acdlabs.typepad.com/elucidation/2008/02/dealing-with-a.html In my lab days, I would routinely workup a newly acquired 1H NMR for an unknown sample prior to acquiring a 2D NMR dataset. One of my goals was to examine...
What is the difference between Profile and Centroid MS data?
MS data collected off an instrument is presented as either profile or centroid mode. Shown below are two mass spectra illustrating an ion cluster for profile data and a centroid mass spectrum created from the profile data. In profile mode, a peak is represented by a collection of signals over several scans. The advantage of...
Rings, Double bonds and triple bonds – clues about an unknown structure
Rings plus Double Bonds Equivalent (RDBE) (also known as the degree/element of unsaturation or index of hydrogen deficiency) can be determined from a Molecular Formula (MF). The calculation provides insight into the number of rings and/or double bonds and/or triple bonds to expect from an unknown structure. RDBE = (# of C) + 1 –...
Valences for Sulfur, Phosphorus and Nitrogen
In light of the posting by Oliver Fiehn’s group (http://fiehnlab.ucdavis.edu/projects/Seven_Golden_Rules/Ring-Double-Bonds/), I’ve decided to blog some compounds I’ve encountered in the lab. Using the 2nd formula from the previous blog (http://acdlabs.typepad.com/elucidation/2008/03/rings-double-bo.html), for some cases the RDBE calculation will work if the correct atom valence is known. Note: the nitrochloroform compound can be drawn more than one...
Examining the 12C and 13C ratio in a Mass spectrum – carbon isotopic abundance
On a mass spectrum, the carbon 13 isotope peak appears at approximately one mass unit higher (the actual mass delta 1.00335) than the carbon 12 ion peak. The intensity of these isotopes is proportional to the relative abundance of the naturally occurring isotopes. The relative abundance of the two isotopes is 12C ≈ 98.9% and...
How to apply the Nitrogen rule to organic compounds
The purpose of the nitrogen rule is to assist with deciphering how many nitrogen atoms are present without any prior information on the molecular formula. Depending on the ionization mode, an odd nominal mass indicates an odd number of nitrogen atoms, e.g. 1,3,5, whereas an even nominal mass indicates an even number of nitrogen atoms,...