Trimethyl phosphate-acetylene interaction: a matrix-isolation infrared and ab initio study

Area of Science:

• Physical Chemistry
• Spectroscopy
• Computational Chemistry

Background:

• Understanding intermolecular interactions is crucial in chemistry.
• Trimethyl phosphate (TMP) and acetylene are relevant molecules for studying bonding.
• Matrix isolation spectroscopy is a powerful technique for studying transient species.

Purpose of the Study:

• To identify and characterize adducts formed between trimethyl phosphate (TMP) and acetylene.
• To investigate the nature of bonding and stabilization energies in these complexes.
• To compare experimental spectroscopic data with computational predictions.

Main Methods:

• Matrix isolation of TMP and acetylene in nitrogen and argon.
• Infrared spectroscopy to detect adduct formation and shifts in vibrational frequencies.
• High-level ab initio computations (HF/6-31G**) to determine structures, energies, and vibrational frequencies.

Main Results:

• Two types of TMP-acetylene adducts were identified: phosphoryl-bonded and alkoxy-bonded complexes.
• A primary hydrogen bond at the phosphoryl oxygen and a secondary H...pi interaction were observed.
• Computational frequencies matched experimental data for TMP modes but less so for acetylene modes.
• Stabilization energies were approximately 3 kcal/mol for the phosphoryl complex and 1 kcal/mol for the alkoxy complex.

Conclusions:

• The study successfully identified and characterized TMP-acetylene complexes using both experimental and computational methods.
• The findings elucidate the specific hydrogen bonding interactions, including a notable H...pi interaction.
• The results provide valuable insights into the energetics and structural properties of these molecular adducts.