222 



6. INTERACTIONS OF INHIBITORS WITH ENZYMES 



Table 6-5 

 Molecular Group Refractions and Dipole Moments " 



" The molar refractions were calculated from the bond refractions in Table 6-2 

 assuming that the group is bonded to a carbon atom. Thus to obtain the change in 

 refraction upon substitution of these groups for a hydrogen atom, the refraction of 

 the C — H bond (1.65) must be subtracted from the values given in the table. The 

 group moments for both phenyl and ethyl derivatives were obtained mainly from 

 Smyth (1955, p. 253) as were the angles that the group dipoles form with the C — group 

 bond axis. The two figures given for the dipole angle of the aminp compounds are 

 for the aliphatic and aromatic situations respectively. 



Dipole-lnduced Dipole Interactions 



A permanent dipole can also polarize a neighboring molecule. The po 

 tential energy of a polarizable molecule in an electrical field is 9? = 

 (Eq. 6-25). The field strength of a permanent dipole is given by: 



ocJV'2 



/' 



d^D 



V" 1 + 3 cos2 



where is defined in Fig. 6-3. The potential energy is thus: 



9 



U^D 



- [1 + 3 cos= d] 



(6-29) 



(6-30) 



When the polarized molecule lies on the dipole axis, 9^ = — 2aQ/.i^ld^D^, 

 and when it lies on a line perpendicular to the dipole and passing through 



