Shapes of Benzyl Benzoate: A Rotational Spectroscopic and Computational Study

Area of Science:

• Physical Chemistry
• Chemical Physics
• Computational Chemistry

Background:

• Understanding intramolecular noncovalent interactions is crucial for predicting the conformational preferences of large semivolatile organic compounds.
• Benzyl benzoate (BnBz) serves as a model ester for investigating these interactions due to its terminal benzyl and phenyl groups.

Purpose of the Study:

• To elucidate the molecular-level insights into how weak intramolecular noncovalent interactions govern the conformational preference of benzyl benzoate.
• To resolve theoretical ambiguities in predicting the stability ordering of BnBz conformers.

Main Methods:

• Chirped-pulse Fourier transform microwave spectroscopy was employed to observe and assign rotational spectra.
• Density Functional Theory (DFT) calculations were used for conformational searches and energy predictions.
• Analysis of noncovalent interactions and conformational conversion barriers was performed.

Main Results:

• Four BnBz conformers were identified, with two low-energy species exhibiting a planar benzoate motif.
• Experimental results confirmed BnBz-g as the global minimum, contradicting some DFT predictions based on different energy corrections.
• A low conformational conversion barrier (<5 kJ mol⁻¹) was experimentally and computationally determined.

Conclusions:

• Experimental data is essential for benchmarking and refining computational predictions of molecular conformations.
• CH···O hydrogen bonds play a significant role in determining the structural preferences of low-energy BnBz conformers.
• The study provides valuable insights into the interplay of noncovalent interactions in shaping the conformational landscape of organic molecules.