Skip To Content

Logic Puzzle #1: The Missing Link

May 27, 2010
by Arvin Moser, Team Manager, Application Scientists, ACD/Labs

A great skill to master is the capability to conceptualize a fragment or structure directly off a spectrum without resorting to paper-and-pen work. This skill is learnt through lots of practice. Whenever partial information is available, an elucidator can conjure up a mental image of possibilities and should it be required instinctively hunt for any missing data.

In the following example, a set of fragments including 13C and 1H chemical shifts and long-range coupling information were extracted from an HMBC experiment (not shown). The green arrows represent the 2-3J coupling responses between the 3 equivalent methyl groups and the carbonyl’s quaternary carbon. Based on these restrictions, what fragment(s) support the data and is there anything missing?

LogicCCH3_1_May272010

 

To accommodate these restrictions, three potential fragments, assigned A, B and C, are shown below. Fragment A can be disregarded on the basis of the carbon valence. Fragment B is not a good candidate because the CH3 chemical shifts do not support the presence of an adjacent heteroatom. Fragment C seems to be the most logical choice. However, there is a missing quaternary carbon. The next step is to re-evaluate the NMR data in search of a weak 13C signal at ~40 ppm.

LogicCCH3_2_May272010

 


Join our newsletter!

Keep up-to-date with our quarterly newsletter that brings you the latest educational webinars, resources, tips, and tricks.

This field is for validation purposes and should be left unchanged.

Comments

Your email address will not be published. Required fields are marked *

Join our newsletter!

Keep up-to-date with our quarterly newsletter that brings you the latest educational webinars, resources, tips, and tricks.

This field is for validation purposes and should be left unchanged.