This paper deals with the topic of biocatalytic synthesis of chiral molecules, i.e. (R)-3- hydroxy-4,4-dimethylpentane nitrile from 3,3-dimethyl-1,2-epoxybutane using the enzyme halohydrin dehalogenase. The synthesis of optically pure substances is an extremely important part of the pharmaceutical industry considering that two enantiomers can have completely different properties, and often one of them can have harmful and toxic biological effects. Epoxides are highly valuable compounds in organic synthesis because the epoxy ring can be chemically transformed into plenty of synthetically useful intermediates. Reactions involving enzymes need to be well investigated and characterized to be carried out on an industrial scale. Given the different activity of enzymes in different reaction conditions (temperature, substrate concentrations, pH, oxygen saturation, presence of cofactor), it is extremely important to know their structure and reaction mechanism in order to determine the most suitable reaction conditions that will allow obtaining maximum yields of the desired product. Mathematical modelling is an excellent tool for conducting research of this kind. It consists of a kinetic model and a mass balance in the reactor. For the development of a mathematical model, the stability of 3,3-dimethyl-1,2-epoxybutane in buffer was determined and it was found that 3,3-dimethyl-1,2-epoxybutane is subject to chemical hydrolysis. Simulations in the package programme Scientist showed that chemical hydrolysis of epoxy have a significant impact on the enzymatic reaction. The most suitable reactor for biocatalytic synthesis of (R)-3-hydroxy-4,4-dimethylpentane nitrile is a fed-batch reactor with a continuous supply of substrate because it enables the selection of working conditions that minimize the effect of substrate inhibition, and working at the substrate concentration that provides the maximum reaction rate.