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4
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84988124546
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Our earliest publicly available program was MM1, and it dealt only with nonconjugated systems. An extended version dealt with conjugated hydrocarbons and ketones (MMP1). These programs are available from the Quantum Chemistry Program Exchange, University of Indiana, Bloomington, IN 47405, as program 318 [(QCPE), 11, 318 (1976)]. Subsequently a better molecular mechanics program was devised by us (MM2). The first application was to saturated hydrocarbons (ref. 5), followed by extension to most common functional groups. This program (MM2/77) is available from QCPE [(QCPE), 12, 395 (1980)]. Still later the conjugated hydrocarbon part of the program was added (as described in the present work). The resulting program is called MM2/82. (We have decided to drop the MMP2 designation. From MM2/82 on, the same program deals with both conjugated and unconjugated systems). The MM2/82 program is available from Molecular Design, Ltd., 2132 Farallon Drive, San Leandro, California 94577, and from QCPE. A still more recent version (MM2/85) is an extension of earlier programs which also includes conjugated heterocycles. It will be available in due course.
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11
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84988113666
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The above description is for the f factor as it appears in MM2/82 and earlier versions of the program. We have found a few cases where the relatively small values of f so calculated permit excessive deformation of pi systems, and thus yield rotational barriers which are too low in a few cases. While this problem will be corrected in MM2/85 and later versions of the program, we wish to alert users of the earlier versions to the potential problem.
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16
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0022645035
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This program has been called MM2P. It has been incorporated in the Prophet Network, and has been widely used by the, e.g.
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(1986)
J. Am. Chem. Soc.
, vol.108
, pp. 207
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Rohrer, D.1
Darden, T.2
McKinney, J.D.3
Gottshalk, K.4
Maynard, A.T.5
Pedersen, L.G.6
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19
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84988138611
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In electron diffraction work the investigator usually gives three times the standard deviation from the error matrix as the probable error, whereas in crystallography the esd's themselves are usually quoted.
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29
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0000367023
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The crystal and molecular structure of 1,1,2,2,9,9,10,10-octafluoro-[2,2]paracyclophane and a reinvestigation of the structure of [2,2]paracyclophane
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(1972)
Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry
, vol.28 B
, pp. 1733
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Hope, H.1
Bernstein, J.2
Trueblood, K.N.3
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35
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84988065012
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J. Chem. Soc. (B)
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(1953)
, pp. 3265
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Brown, C.J.1
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41
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84988065013
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J. Chem. Soc. (B)
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(1953)
, pp. 3278
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Brown, C.J.1
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58
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0001741003
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The Single and Double Bonds Between sp2-Hydridized Carbon Atoms, as Studied by the Gas Electron Diffraction Method. VIII. The Molecular Structure of 1,3-Cycloheptadiene.
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(1972)
Acta Chemica Scandinavica
, vol.26
, pp. 3643
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Hagen, K.1
Traetteberg, M.2
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59
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84988138521
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The force‐field parameters were chosen for typical molecules, to take butadiene as an example, so as to fit the steric energy differences between the cis and trans isomers, and the transition state separating them. Later, when the heats of formation of molecules were worked out, the calculation was based on the stable form, the trans isomer in the case of butadiene. This leads to an inconsistency, which was not recognized until several years after this work was finished and the program had been widely distributed. The inconsistency is that the pi electronic energy is used to calculate the heat of formation. If one calculates the heat of formation of the cis butadiene, because this number is slightly different from that of the trans isomer, (one gets a heat of formation which is not quite consistent with that which one would get from calculation of the heat of formation of the trans isomer). This is a common problem in all of the heat of formation calculations. Fortunately, the errors are small, on the order of tenths of kcals as far as we are aware. But if one is comparing systems which quite different electronic energies, let's say, for example, a molecule which has in one arrangement bonds of equal bond length, and in a second arrangement, alternating long and short bonds, the bulk of the difference between these two geometries will be reflected in the heat of formation, but not in the steric energies. Hence, in real cases, the heats of formation differences and steric energy differences may give somewhat different results. Which result is better will depend on the nature of a case at hand.
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67
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37049120429
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This is true according to rotational barriers in substituted binaphthyl systems. See, J. Chem. Soc. C
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(1967)
, pp. 988
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Cooke, A.S.1
Harris, M.M.2
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