A- and B-type hydrogen bond modifications of potassium hydrogen tartronate
ACCORDING to Speakman1 two types of intermolecular hydrogen bonds between carboxyl groups can be discerned in the crystal structures of acid salts of carboxylic acids. The first, type B, occurs when two carboxyl groups are not symmetry related, and have structural differences sufficient to characterise them, separately, as unionised (−CO2H) and ionised (−CO2−). Thus, any hydrogen bond between these groups must be asymmetric. The second, type A, occurs when two carboxyl groups are related by a symmetry element of the crystal, so that they are effectively equivalent. Thus any hydrogen bond between the groups must be, at least formally, symmetrical.
Non-hydrogen-bonded Hydroxyl Groups in Crystals
AN intermolecular O—H … O contact is usually described as a hydrogen bond if the distance between the oxygen atoms is less than about 3.0 Å, and on the basis of this criterion many X-ray structure investigations have prompted the conclusion that a free hydroxyl group in crystalline hydroxy compounds will be rare1.
Impact of acetaldehyde‐ and pyruvic acid‐bound sulphur dioxide on wine lactic acid bacteria
Aims:  To investigate the impact of acetaldehyde‐ and pyruvic acid‐bound sulphur dioxide on wine lactic acid bacteria (LAB).