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Force field calculations using MM3 have been extended to include carboxylic acids and esters. Accurate structures for several small molecules were well reproduced, and vibrational spectra moderately so. Available thermochemical data were examined. A good portion of them were rejected as inaccurate, and the remainder were fit. (1) Burkert, U.; Allinger, N. L. Molecular Mechanics; American Chemical Society: Washington, DC, 1982. (2) Allinger, N. L.; Yuh, Y. H.; Lii, J.-H. J. Am. Chem. SOC. 1989, 111, 8551, 8566, 8576. The MM3 program is available to all users from the Technical Utilization Corp. Inc., 235 Glen Village Court, Powell, Ohio 43065, and to commercial users only from T r i p Associates, 1699 South Hanley Rd, St. Louis, MO 63144, and to academic users only from the Quantum Chemistry Program Exchange, University of Indiana, Bloomington, IN 47405. The current version is available to run on most types of computers, and interested parties should contact one of the distributors directly. (3) (a) Allinger, N. L.; Rahman, M.; Lii, J.-H.

Simple alcohols and ethers have been studied with the MM4 force field. The structures of 13 molecules have been well fit using the MM4 force field. Moments of inertia have been fit with rms percentage errors as indicated: 18 moments for ethers, 0.28%; 21 moments for alcohols, 0.22%. Rotational barriers and conformational equilibria have also been examined, and the experimental and ab initio results are reproduced substantially better with MM4 than they were with MM3. Much of the improvement comes from the use of additional interaction terms in the force constant matrix, of which the torsion-bend and torsion-torsion are particularly important. Induced dipoles are included in the calculation, and dipole moments are reasonably well fit. It has been possible for the first time to fit conformational energetic data for both open chain and cyclic alcohols (e.g., propanol and cyclohexanol) with the same parameter set. For vibrational spectra, over a total of 82 frequencies, the rms error is 27 cm(-1), as opposed to 38 cm(-1) with MM3. Both the alpha and beta bond shortening resulting from the presence of the electronegative oxygen atom in the molecule are well reproduced. The electronegativity of the oxygen is sufficient that one must also include not only the alpha and beta electronegativity effects on bond lengths, but also on angle distortions, if structures are to be well reproduced. The heats of formation of 32 alcohols and ethers were fit overall to within experimental error (weighted standard deviation error 0.26 kcal/mol).