1H NMR Archives - ACD/Labs

Exchangeable Protons in NMR—Friend or Foe?

Arvin Moser Jan 26, 2023

Due to their broad peaks and wide range of chemical shifts in ¹H NMR spectra, exchangeable protons are known to pose challenges in NMR interpretation, but collecting 2D spectra and selecting proper experimental conditions can sometimes be used in our favor to learn more.

The Basics of Interpreting a Proton (¹H) NMR Spectrum

Sanji Bhal Dec 2, 2021

¹H NMR is the go-to technique to help identify or confirm the structure of organic compounds. A solution-state proton spectrum is relatively fast to acquire and a lot of information about the structure of a compound can be deduced from it. With centuries of combined experience in NMR data interpretation, we thought we’d share the basics of analyzing solution-phase ¹H NMR spectra in this blog.

Chasing 1H-1H Coupling Constants

Arvin Moser Apr 3, 2019

Coupling constants from a 1D NMR spectrum can be very useful to a chemist when trying to characterize a structure. However, there are cases where the perceived coupling constants can be misleading and thus wrong. The 1H NMR spectrum below shows several multiplets for a major component tryptophan and a minor component. For tryptophan, the...

Compound Identification for Natural Products and Synthetic Compounds

Arvin Moser Oct 7, 2015

In collaboration with Sequoia Sciences Inc., we developed a strategy for the dereplication of a complete or a partial structure using 1H NMR, 1H–13C HSQC and 1H–1H COSY spectral data, a molecular formula composition range and structural fragments against a massive database of about 22 million compounds is considered. The work was based on 18...

Logic Puzzle #42: How to Convert to PPM for NMR and MS Data? … Solution

Arvin Moser Jun 11, 2013

Many analytical data rely on common calculations. This solution shows the formula used in the calculations. NMR and MS data were collected on two unknown compounds. The TOF-MS data shows the [M+H]+ at m/z 300.0000 and 600.000 at an error of 0.001 Da. The 500 MHz 1H NMR spectrum shows two chemical shifts at 1500.00...

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

Arvin Moser Apr 2, 2013

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 #40: What Fragment is This?

Arvin Moser Mar 7, 2013

An experienced elucidator can recognize spectral patterns and use this information to piece together a fragment. This puzzle examines one such pattern-to-fragment connection. A 1H NMR spectrum below shows the aromatic region for an unknown compound? Can you identify the fragment that would produce this pattern?

Logic Puzzle #34: Too Much or Too Little, Where is the Happy Middle? … Solution

Arvin Moser Aug 30, 2012

A good approach is to check and compare your experimental data before and after processing to ensure no information is lost. The 1H NMR spectrum below shows two signals at 7.34 and 7.37 ppm. At 0.2 Hz line broadening (LB), the spectrum (bottom) shows two signals as two singlets. With no line broadening, the spectrum...

Logic Puzzle #34: Too Much or Too Little? Where is the Happy Middle?

Arvin Moser Aug 3, 2012

Post data processing can both be a good thing or a bad thing. With any experimental data, too much processing can affect some critical pieces of information. A 1H NMR spectrum was collected for an unknown compound. An exponential function was applied to the data to help improve the signal-to-noise. A line broadening of 0.0...

Logic Puzzle #30: Unknown Coupling Pattern … Solution

Arvin Moser May 29, 2012

Coupling patterns that overlap can be deceptively simple. There are two possible coupling patterns for the CH2 signal at 3.39 ppm (top spectrum): a singlet or two ‘doublets’ (AB spin system) tilted towards each other. The bottom spectrum shows an example of two ‘doublets’ where the outer signals at 3.34 and 3.43 ppm are barely...

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