The distribution of valence electrons, which are the outermost electrons in organic molecules, has been studied for the first time experimentally. Since these electrons play a key role in atom interactions, this discovery enhances our understanding of chemical bonds, which is significant for both pharmaceuticals and chemical engineering.
For the first time, a team from Nagoya University in Japan has experimentally examined the distribution of valence electrons in organic molecules. Valence electrons govern atomic interactions and, therefore, this discovery sheds light on the essential characteristics of chemical bonding, which could have important ramifications for pharmacy and chemical engineering. The findings have been published in the Journal of the American Chemical Society.
The behavior of electrons in atoms is intricate, involving electron orbitals that function differently based on their distance from the nucleus. Core electrons, which are found in the inner shell, contribute to the atom’s stability and do not engage with other atoms. Conversely, outer electrons, or valence electrons, largely determine a material’s characteristics during bonding with other atoms.
To grasp a material’s properties, it’s crucial to obtain data on its valence electrons. However, isolating this information experimentally has presented challenges, often forcing researchers to depend on theoretical models and spectroscopy for estimates.
Through high-level synchrotron X-ray diffraction experiments at SPring-8, the researchers discovered a way to selectively extract only the valence electron density from atoms in a crystal.
Hiroshi Sawa, the study’s lead author, mentioned, “We referred to this method as the CDFS method. By using it, we examined the electron state of the glycine molecule, which is an amino acid. Although the method is relatively straightforward, the results were remarkable. The electron cloud we observed did not exhibit the smooth, encompassing shape that many expected; instead, it appeared fragmented and discrete.”
To better understand these findings, the team created a color map of their observations. In chemistry, a color map visually represents variations in datasets using colors over a specific range, often paired with spectroscopic methods, imaging, and chemical analyses, facilitating the interpretation of complex data.
The cross-sectional view depicted in their detailed diagram clearly displayed disruptions in the electron distribution surrounding carbon atoms. “When carbon atoms form bonds with neighboring atoms, they modify their electron cloud to generate hybridized orbitals. In this situation, the outermost L-shell electrons create nodes due to their wave characteristics known as wave functions,” Sawa explained. “This indicates that, as a result of electrons’ wave nature, certain areas within the hybrid orbitals lack electrons, contrasting sharply with the common perception of a uniform ‘cloud’ of electrons.”
The observed fragmented electron distribution reflects the electrons’ quantum mechanical wave nature, as physics predicts. To verify the accuracy of their findings, the team carried out advanced quantum chemical calculations in partnership with Hokkaido University, confirming that the experimental data aligned perfectly with theoretical results.
Sawa asserts that this research highlights the value of interdisciplinary collaboration. “I believe this has provided clarity to the previously ambiguous understanding of bonding states that has challenged scientists since the 1800s,” Sawa stated. “Visualizing electron behavior remains a complicated task, yet the outcomes can be elegantly interpreted as electrons behaving in accordance with wave functions. Our discoveries have surprised many researchers and supported the model suggested by quantum chemistry.”
With a deep understanding of the valence electron density for this molecule, the team proceeded with similar experiments and calculations on cytidine, a slightly more complex molecule. They successfully extracted electrons from carbon double bonds and noted clear distinctions between carbon-carbon and carbon-nitrogen bonds.
“This research has enabled a direct visualization of the essence of chemical bonds, potentially aiding in designing functional materials and understanding reaction mechanisms. This approach assists in discussing the electronic states of molecules, which can be challenging to deduce from simply their chemical structure,” Sawa noted. “This may help to clarify why some medications are effective while others are not. Areas influenced by interactions affecting functionality and structural stability, such as organic semiconductors and studies on the structure of DNA double helices, are likely to reap the most benefits from our findings.”
