The first thermodynamics in the world with regard to hemoglobin (12)

conformation

In contrast to the molecule's costitution and the configuration that forms molecule,
conformation represents the three-dimensional position of atoms and groups of atoms in a molecule.

Many molecules are uniquely identified by their constitution and configuration.
Normally, an unambiguously identified molecule has a plurality of conformation.
Even if the molecule is unambiguously identified, it will have various conformations, 
due to rotation or inversion of the combined hand and steric hindrance, etc. 
and conversion of a cyclic compound between a chair type and a boat type.

Reference:

Reaktionen und Synthesen im organish-chemischen
Written by Lutz Friedjan Tietze und Theophil Eicher  
Traslated by Seiichi Takano and Kunirou Ogasawara  
NANKODO Co., Ltd.