1,2-Dichoroethane (DCE) is a prototypical molecule for studying electrostatic solvent effects on molecular conformation as far as rotation around the carbon-carbon bond notably changes the electric properties of the molecule and especially the dipole moment. While the apolar trans conformation is the absolute free energy minimum in the gas phase, solvents of increased polarity relatively favor the population of the gauche conformers. DCE is also a substrate of haloakane dehalogenase from Xanthobacter Autotrophicus (Dh1A), an enzyme that catalyzes the conversion of DCE to 2-chloroethanol. We here investigate the nature of substrate-enzyme interactions, obtaining the free energy profiles of rotation around the C-C bond in the gas phase, in aqueous solution, and in the enzymic environment. In the enzyme only the gauche conformers are free energy minima, the trans conformer being a free energy maximum. Differences between the aqueous solution and enzyme energy profiles are rationalized taking into account the different magnitudes and orientations of the electric field created by the environment in both cases. In aqueous solution DCE feels a reaction field several times lower in modulus than in the enzyme active site. Consequences on enzyme catalysis are also discussed.