Quantitative correlation between CD bond length and CD stretching frequency in deuterated organic molecules: A combined quantum chemical and vibrational spectroscopic study.

Abstract

The relationship between chemical bond length and vibrational frequency provides an important link between molecular structure and vibrational spectroscopy. However, a quantitative relationship between CD bond length and CD stretching frequency has not been systematically established. Here, we investigate this relationship using quantum chemical calculations for 132 chemically diverse organic molecules, comprising 5006 CD bonds. A strong linear correlation was obtained, yielding an empirical relationship with R2 = 0.9772. The relationship enables conversion between CD stretching frequencies and bond lengths and was validated using independent molecular systems. For phenylalanine-water clusters and lactic acid conformers, predicted frequencies and bond lengths agree closely with directly calculated values. Its applicability to experimental systems was further demonstrated using Raman spectra of mono-deuterated isoprenol and FTIR spectra of deuterated molecular crystals. For 4FH-ZnCl2 and 4FCl-ZnI2, CD bond lengths derived from FTIR frequencies agree with neutron-diffraction measurements with an RMSE of 5.1 mÅ. Although the general applicability of the linear correlation requires further validation because of the limited computational dataset and experimental test systems considered in this study, the relationship nevertheless demonstrates the potential of CD stretching spectroscopy as a sensitive probe of molecular structure, molecular interactions, and conformation.

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