: an inversion of configuration of one optically active compound into another that may or may not lead to a change in the direction of optical rotation and that may be of either of two general types:                                      
                
                    
           
           
      
              
        a
    
                                          
              
          
                                                      : inversion involving two reactions in which an optically active compound is changed to another by substitution at its asymmetric center and then regenerated (as dextro-alanine is changed to levo-bromo-propionic acid by nitrosyl bromide and then to levo-alanine by ammonia) but as the optical isomer of the original compound                                      
                
                    
            
      
              
        b
    
                                          
              
          
                                                      : inversion involving one reaction of an optically active compound at its asymmetric center with resulting configurational change from d to l or vice versa regardless of change in optical rotation (as from levorotatory l-bromo-propionic acid to levorotatory d-alanine by ammonia but not from dextrorotatory l-alanine to levorotatory l-bromo-propionic acid because no inversion of configuration occurs although optical inversion does)                                      
                
                    
            
   
                   
             
                    
                        
        
        
        
                
                
                
        
                
     
    
                                                    
                                                                                                                    
            
                                    
                        
                                                    
                                
                       
                                        
                
                                                
                            
            
                                    
                                    
                        
                                            
                                                            
                                    
                                                                
                                
                                    
                
                
                
                
                
                
                
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
                                        
                                                    
                            
                                                               
                                                
  
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  Merriam-Webster unabridged
 
                          
                    
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