Competitive tetrel bond and hydrogen bond in benzaldehyde–CO 2 : characterization via rotational spectroscopy

The rotational spectrum of the 1 : 1 benzaldehyde–CO 2 complex has been investigated using pulsed-jet Fourier transform microwave spectroscopy complemented with quantum chemical calculations.

The rotational spectrum of the 1 : 1 benzaldehyde–CO 2 complex has been investigated using pulsed-jet Fourier transform microwave spectroscopy complemented with quantum chemical calculations. Two isomers, both characterized by one C⋯O tetrel bond (n → π interaction) and one C–H⋯O hydrogen bond (n → σ interaction), have been observed in the pulsed jet. Competition between the tetrel bond and the hydrogen bond has been disclosed by natural bond orbital analysis: isomer I is characterized by one dominating OC CO 2 ⋯O tetrel bond (12.6 kJ mol −1 ) and a secondary (C–H) formyl ⋯O hydrogen bond (2.2 kJ mol −1 ); by contrast, in isomer II the (C–H) phenyl ⋯O hydrogen bond (7.6 kJ mol −1 ) becomes the dominant bond, while the OC CO 2 ⋯O tetrel bond (5.8 kJ mol −1 ) becomes much weaker with respect to that of isomer I. Using intensity measurements the relative population ratio of the two isomers was estimated to be N I / N II ≈ 2/1.

The rotational spectrum of the 1 : 1 benzaldehyde–CO 2 complex has been investigated using pulsed-jet Fourier transform microwave spectroscopy complemented with quantum chemical calculations.

The rotational spectrum of the 1 : 1 benzaldehyde–CO 2 complex has been investigated using pulsed-jet Fourier transform microwave spectroscopy complemented with quantum chemical calculations. Two isomers, both characterized by one C⋯O tetrel bond (n → π interaction) and one C–H⋯O hydrogen bond (n → σ interaction), have been observed in the pulsed jet. Competition between the tetrel bond and the hydrogen bond has been disclosed by natural bond orbital analysis: isomer I is characterized by one dominating OC CO 2 ⋯O tetrel bond (12.6 kJ mol −1 ) and a secondary (C–H) formyl ⋯O hydrogen bond (2.2 kJ mol −1 ); by contrast, in isomer II the (C–H) phenyl ⋯O hydrogen bond (7.6 kJ mol −1 ) becomes the dominant bond, while the OC CO 2 ⋯O tetrel bond (5.8 kJ mol −1 ) becomes much weaker with respect to that of isomer I. Using intensity measurements the relative population ratio of the two isomers was estimated to be N I / N II ≈ 2/1.