Molecular mechanics Allinger force fields

MM3 Molecular mechanics, Allinger force field version 3... 

Still another method designed for the same purpose, namely equilibrium ground state geometries, must be mentioned. Starting with Westheimer s early calculations [141], the molecular mechanics or force field methods became a very important tool, especially for very large molecular systems, as encountered in biochemical applications. Here the contributions by Lifson/Warshel [142] and Allinger [143] deserve attention. 

T and N L Allinger 1989. Molecular Mechanics. The MM3 Force Field for Hydrocarbons. 2. Vibra-ional Frequencies and Thermodynamics. Journal of the American Chemical Society 111 8566-8582. on F 1930. Zur Theori und Systematik der Molekularkrafte. Zeitschrift fur Physik 63 245-279. 

The original molecular-mechanics force field was developed by Allinger, and is generally referred to as MM. You should read the definitive text by Burkert and Allinger (1982) for more details. This model was followed by the MM2 model (Allinger, 1977), and I thought that you might like to read the synopsis. 

The use of molecular mechanics calculations has become common practice in chemical research since the early 80s, when general-purpose force fields, incorporated into user-oriented computer programs, started to appear (Figure 1). As noted above, the most popular and extensively used force fields are undoubtedly those developed by Allinger s group, namely MMI (early 70s), MM2 (1977-) and, more recently, MM3 (1988-). 

Lii JH, Allinger NL. Molecular mechanics. The MM3 force field for hydrocarbons. 2. Vibrational frequencies and thermodynamics. J Am Chem Soc 1989 111 8566-8575. 

In this connection, a very recent paper by Allinger (8) should be mentioned. A force field has been developed to permit molecular mechanics calculations on various molecular structures of elemental sulfur. The conformational characteristics of sulfur rings containing five to 12, 14, 16, 18, or 20 sulfur atoms have been examined. Comparison with experimental data is made in all cases where such data exist, and predictions are made for other cases. Ab initio molecular orbital calculations using an STO-3G basis set were carried out for cyclohexasulfur and are consistent with the molecular mechanics calculations in indicating that the chair and the twist forms are two stable conformations, with the chair about 15 kcal/mol more stable while the boat (C2t,) is a twist rotational transition state. Calculation of possible conformations of the pro-... 

Perhydrotriquinacene 358) has a gas-phase enthalpy of formation of —102.39 kJ mol-1,379 suggesting that the latent strain in the pentagonal dodeca-hedrane molecule should be rather lower than that predicted by Allinger s force field calculations380 and somewhat more comparable to the molecular mechanics prediction advanced by Schleyer.381 The existing discrepancy arises because both... 

Enthalpies of formation may be calculated with parameters derived from molecular mechanics force fields. See U. Burkert and N. L. Allinger, Molecular Mechanics, American Chemical Society, Washington, D. C., 1982 N. L. Allinger, Y. H. Yuh, and J-H. Lii, J. Amer. Chem. Soc., Ill (1989) 8551 N. L. Allinger, X-F. Zhou, and J. Bargsma, Theochem-J. Molec. Structure, 118 (1994)69. 

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