This binding limits configurational and rotational freedom. The distinction between configurational and non-configurational languages can exist for phrase structure grammars only. The configurational or strain energy can be estimated using molecular mechanics calculations. In the , glyceraldehyde is used as the configurational standard for carbohydrates. The configurational approach is limited in what it can accomplish. Similar configurational notions had been circulating for more than a decade. C-command is a configurational notion; it is defined over concrete syntactic configurations. C-command is a configurational notion that acknowledges the syntactic configuration as primitive. The configurational head loss, formula 2, can be calculated using the following equation. The configurational stability of a drug is therefore an area of interest in pharmaceutical research. E/Z isomers, which have restricted rotation at a double bond, are configurational isomers. In 1964, Klima defined a configurational relationship between nodes he labeled "in construction with".