Intermolecular interaction in the formaldehyde-dimethyl ether and formaldehyde-dimethyl sulfide complexes investigated by Fourier transform microwave spectroscopy and ab initio calculations.

The ground-state rotational spectra of the formaldehyde-dimethyl ether (H2CO-DME) and formaldehyde-dimethyl sulfide (H2CO-DMS) complexes have been studied by Fourier transform microwave spectroscopy. The a-type and c-type rotational transitions have been assigned for the normal and deutrated formaldehyde-containing species of both complexes. In the case of H2CO-DME, doublets were observed with the splitting 10-300 kHz, whereas no such splittings were observed for H2CO-DMS, D2CO-DME, and D2CO-DMS. The observed rotational spectra were found consistent with a structure of Cs symmetry with DME or DMS bound to H2CO by two types of hydrogen bonds: C-H(DME/DMS)---O(H2CO) and O(DME)/S(DMS)---H-C(H2CO). The R(cm) distances between the centers of mass of the component molecules in the H2CO-DME and H2CO-DMS complexes were determined to be 3.102 and 3.200 Å, respectively, which are shorter than those in most related complexes. The spectral and NBO analyses showed that H2CO-DMS has a stronger charge transfer interaction than H2CO-DME does and that the binding energy of H2CO-DMS is larger than that of H2CO-DME.

Strain-induced regioselectivities in reactions of benzyne possessing a fused four-membered ring.

[reaction: see text] A fused four-membered ring has a powerful directing ability in effecting the regioselective reactions of benzyne with ketene silyl acetal, nucleophile, and alpha-alkoxyfuran.