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IR Frequency Region: Fingerprint Region

IR Frequency Region: Fingerprint Region

IR spectra are divided into two main regions: the diagnostic region and the fingerprint region. The diagnostic region of the spectrum lies above 1500 cm−1. The absorptions resulting from single-bond vibrations of the N–H, C–H, and O–H stretch at higher wavenumbers and appear on the left side of the spectrum. The stretching absorptions of the C≡C and C≡N occur between 2100–2300 cm−1. In contrast, those arising from stretching absorptions of the C=O, C=N, and C=C occur between 1600–1850 cm−1.
The...

Chemical Shift: Internal References and Solvent Effects

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In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
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¹³C NMR: ¹H–¹³C Decoupling

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The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
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Related Experiment Video

Updated: Jul 5, 2026

Chromatographic Fingerprinting by Template Matching for Data Collected by Comprehensive Two-Dimensional Gas Chromatography

Chromatographic Fingerprinting by Template Matching for Data Collected by Comprehensive Two-Dimensional Gas Chromatography

Published on: September 2, 2020

Random reduction in fingerprint bit density improves compound recall in search calculations using complex reference

Yuan Wang¹, Hanna Geppert, Jürgen Bajorath

¹Department of Life Science Informatics, B-IT, LIMES Program Unit Chemical Biology and Medicinal Chemistry, Rheinische Friedrich-Wilhelms-Universität Bonn, Dahlmannstr. 2, D-53113 Bonn, Germany.

Chemical Biology & Drug Design

|May 10, 2008

Summary

Complex molecular fingerprints reduce search performance. Randomly deleting bits from complex fingerprints can improve recall, despite some information loss, suggesting a new search strategy for molecular discovery.

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Area of Science:

Computational chemistry
Cheminformatics
Drug discovery

Background:

Molecular fingerprints are essential for searching chemical databases.
Existing methods face challenges with molecular complexity and size, leading to search errors.
Complex molecules as templates can lead to biased recognition of larger compounds.

Purpose of the Study:

To systematically investigate the impact of molecular complexity on fingerprint similarity searching.
To develop strategies for improving search performance with complex reference molecules.

Main Methods:

Designed sets of active molecules with varying fingerprint bit densities.
Conducted systematic similarity search trials using these molecules.
Analyzed the relationship between molecular complexity and search performance.

Main Results:

Increased molecular complexity of reference molecules correlates with decreased search performance.
Random deletion of set bits in complex fingerprints generally enhances compound recall.
Bit deletion leads to a reduction in the chemical information content of fingerprints.

Conclusions:

Molecular complexity significantly impacts fingerprint search efficacy.
Random bit deletion offers a potential strategy to mitigate complexity-related search issues.
Optimized active compounds as references necessitate search strategies sensitive to complexity effects.