# ACD/Labs Blog

## Logic Puzzle #40: What Fragment is This? … Solution

Logical reasoning and pattern recognition form the basis for making a pattern-to-fragment connection. For an unknown, the 1H NMR spectrum below shows 5 multiplets in the aromatic region. The multiplet at 7.57 ppm shows two overlapping multiplets: a broad signal overlapping a ‘doublet’ (noted as d*). Based on the multiplets’ tilt/lean and integrals, a 1,2-disubstituted...

## Logic Puzzle #2: How to link 3 Fragments

The goal of this puzzle is to logically combine a set of fragments using valence and NMR information. In this puzzle, three fragments are correlated through 2-3J coupling responses (represented by a green arrow) that were extracted from a 1H-13C HMBC data (spectrum not shown). The carbon atoms with the 13C chemical shifts displayed in...

## Logic Puzzle #1: The Missing Link

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...

## Ah Sugar, Sugar … Residue

Sugar residues (saccharides) can be tough to elucidate. They tend to have 1H NMR spectrum with overlapping and sometimes poorly-resolved 1H signals, and the 2D NMR data presents lots of ambiguous assignments. With a little practice, an elucidator can quickly pick out a sugar moiety based on a minimal amount of NMR data. For a...

## Qualitative Elucidation via TLC Staining

TLC (Thin Layer Chromatography) offers a simple approach to identifying a solvent(s) for separating out a mixture, monitoring a reaction to completion, etc. Furthermore, the TLC plates can be stained to identify the presence or absence of various functional groups such as amines, ketones, etc. This qualitative experiment does offer various drawbacks. The process of...

## Re-evaluating the data from MS and NMR … Part 4

With any type of data, there is an inherent risk of misinterpretation. My advice to elucidators is to consider multiple solutions and examine each one thoroughly. In the end, the answer to any problem set lies in tying together the bits of information in hopes of understanding the bigger picture. Recap of the problem: The...

## Re-evaluating the data from MS and NMR … Part 2

Whenever data appear to contradict each other, an instinctive reaction to this problem is to collect more data. Collecting more data can help to understand the problem and/or complicate the matter. Remember the model for Elucidation Evolution? Maximize data extraction (MDE) while minimizing data collection (MDC). Recap of the problem: The ESI+ MS shows a...

## Re-evaluating the data from MS and NMR … Part 1

Structure elucidators will routinely use data from multiple techniques such as MS and NMR to build a proposed structure(s). When dealing with data from multiple techniques, the issue may arise that the data seem to contradict each other. In these cases, it is best to step back and re-evaluate the data from a different angle....

## Determining the Site of Modification … Part 2

Peak matching involves the process of comparing spectral data from a parent or starting material to an unknown compound. (The unknown compound can be referred more specifically as the product, impurity, degradant, metabolite, etc.). The similarities between the data indicate regions that have not changed while the differences indicate regions of change. The full scan...

## Determining the Site of Modification … Part 1

In past blogs, I have ascribed the process of peak matching as an integral part of structure elucidation. In this series, peak matching is demonstrated with the use of MS data. The scheme below shows a parent compound (2-oxo-N,2-diphenylacetamide) with two possible sites for hydrogenation. The potential modified compounds are 2-hydroxy-N,2-diphenylacetamide and 2-hydroxy-1-phenyl-2-(phenylamino)ethanone labeled A...