The basic principles of MM

The bond stretching term. The increase in the energy of a spring (remember that we are modelling the molecule as a collection of balls held together by springs) when it is 

Ahristopher K. Ingold, born London 1893. D.Sc. London 1921. Professor Leeds, London. Knighted 1958. Died London 1970. 

Norman L. Allinger, bom Rochester New York, 1930. Ph.D. University of CaUfornia at Los Angeles, 1954. Professor Wayne State University, University of Georgia. 

If we take the energy corresponding to the equilibrium length /eq as the zero of energy, we can replace A stretch by suetch  

The nonbonded interactions term. This represents the change in potential energy with distance apart of atoms A and B that are not directly bonded (as in A-B) and are not bonded to a common atom (as in A-X-B) these atoms, separated by at least two atoms (A-X-Y-B) or even in different molecules, are said to be nonbonded (with respect to each other). Note that the A-B case is accounted for by the bond stretching term stretch and the A-X-B term by the angle bending term bend. but the nonbonded term nonbond is, for the A-X-Y-B case, superimposed upon the torsional term torsion we can think of lorsion as representing some factor inherent to resistance to rotation about a (usually single) bond X-Y (MM does not attempt to explain the theoretical, electronic basis of this or any other effect), while for certain atoms attached to X and Y there may also be nonbonded interactions. 

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This chapter explains the basic principles of MM, which rests on a view of molecules as balls held together by springs. MM began in the 1940s with attempts to analyze the rates of racemization of biphenyls and Sn2 reactions. 

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