The conformational behaviour of free d-glucose—at last†
The conformational behaviour of isolated D-glucose has been revealed in this work using Fourier transform microwave spectroscopy coupled with laser ablation of crystalline α- and β-glucopyranose samples. Four conformers of α-D-glucopyranose and three of β-D-glucopyranose have been unequivocally identified on the basis of the spectroscopic rotational parameters in conjunction with ab initio predictions. Stereoelectronic hyperconjugative factors, like those associated with anomeric or gauche effects, as well as the cooperative OH⋯O chains extended along the entire molecule, are the main factors driving the conformational behaviour. The most abundant conformers exhibit a counter-clockwise arrangement (cc) of the network of intramolecular hydrogen bonds.