What question did this study set out to answer?

To measure the internal rotation dynamics and quantify the torsional potential energy barriers of ring methyl groups in jet-cooled toluene and the three xylene isomers in both ground and excited electronic states.

August 15, 1987The Journal of Chemical Physics

A study of nonrigid aromatic molecules by supersonic molecular jet spectroscopy. I. Toluene and the xylenes

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To measure the internal rotation dynamics and quantify the torsional potential energy barriers of ring methyl groups in jet-cooled toluene and the three xylene isomers in both ground and excited electronic states.
Measured dispersed emission and time-of-flight mass spectra of jet-cooled toluene, ortho-xylene, meta-xylene, and para-xylene within 100 cm⁻¹ of the S1 ⇄ S0 origins.
Applied a one-dimensional rigid rotor model to spectral line spacings to calculate methyl rotational constants and n-fold potential barrier parameters.
Carried out empirical force field calculations using a molecular orbital–molecular mechanics algorithm to model conformational barrier values.
Toluene and p-xylene exhibited low rotational barriers in both the ground state (V6 ~10 cm⁻¹) and S1 excited state (V6 ~25 cm⁻¹).
m-Xylene showed a low ground-state barrier (V6 ~25 cm⁻¹) and a higher excited-state barrier of V3 = 81 cm⁻¹ and V6 = -30 cm⁻¹.
o-Xylene demonstrated the highest rotational hindrance, with a ground-state barrier of V3 = 425 cm⁻¹ and V6 = 18 cm⁻¹, shifting to V3 ~166 cm⁻¹, V'3 ~-25 cm⁻¹, and V6 ~0 cm⁻¹ in the excited state with a kinetic coupling coefficient of 0.72.

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Implication

Spectroscopy reveals internal methyl rotation barriers across electronic states in toluene and xylene isomers, demonstrating that steric interactions dictate rotational freedom.

Cite This Study

Breen et al. (1987) studied this question.

synapsesocial.com/papers/6a87e9cc70098fa105bb5f3c https://doi.org/10.1063/1.453164

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Implication

Spectroscopy reveals internal methyl rotation barriers across electronic states in toluene and xylene isomers, demonstrating that steric interactions dictate rotational freedom.

A study of nonrigid aromatic molecules by supersonic molecular jet spectroscopy. I. Toluene and the xylenes

Key Points

Discussion

Implication

Cite This Study

A study of nonrigid aromatic molecules by supersonic molecular jet spectroscopy. I. Toluene and the xylenes

Key Points

Discussion

Implication

Cite This Study

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