15 



MESOMERIG CONCEPTS 

 IN THE BIOLOGICAL 



SCIENCES 



HERMAN M. KALCKAR, member of the research staff, division 



OF NUTRITION AND PHYSIOLOGY, THE PUBLIC HEALTH RESEARCH INSTITUTE 



OF THE CITY OF NEW YORK, INC. 



l\TO CHEMIST would question that the concept of meso- 

 -^ » merism (or resonance), a concept which is actually based 

 on quantum mechanics, has played an overwhelmingly important role 

 in the development of modern physical and organic chemistry. This 

 concept has made it possible to understand and explain the properties 

 of numerous inorganic and organic compounds, and in a number of 

 cases to predict chemical events. There are many indications that this 

 concept will play an equally significant role in the biological sciences, 

 and for that reason it merits the consideration of biologists. 



Mesomerism 



The terms resonance and mesomerism are synonomous. The 

 former is based on quantum mechanical concepts, while the latter, 

 more neutral term merely indicates that a substance exists as a hybrid 

 of at least two more or less symmetric electronic states. The term 

 "mesomerism" is more appropriate in a biological essay in which the 

 symbols and formulas are not those of quantum mechanics, and will 

 therefore be used here. 



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