Consider the electrostatic model of the hydrogen bond. Th e N–C distance of the hydrogen bonded groups in proteins, such as occur in an a helix, is 0.29 nm. How much energy (in kJ mol−1 ) is required to break the hydrogen bond (a) in a vacuum (εr = 1), (b) in a membrane (essentially a liquid hydrocarbon with εr = 2.0), and (c) in water (εr = 80.0)?