摘要:

AbstractFour minimal Gaussian basis sets are generated for the second‐row atoms Li through Ne. The first one, MINI‐1, consists of a 3‐term contraction of primitive Gaussian‐type orbitals for 1s, 2s, and 2patomic orbitals. The convenient shorthand notation would be (3,3) for LiBe and (3,3/3) for BNe. The second one, MINI‐2, can be represented by (3,3/4) for BNe. In the same way, MINI‐3 is described as (4,3) for LiBe, and MINI‐3 and MINI‐4 are represented by (4,3/3) and (4,3/4) for BNe, respectively. Although the four basis sets are the minimal type, they give the valence shell orbital energies which are close to those of DZ. These four and other sets derived from them are tested for the hetero‐ and homodiatomic molecules and some organic molecules. They are found to give the orbital energies that agree well with those given by extended calculations. Atomization energies and other spectroscopic constants are also calculated and compared with those of extended calculations. The results clearly indicate that the present basis sets can be used very effectively in

ISSN:0192-8651    

DOI:10.1002/jcc.540010302

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractCahn–Ingold–Prelog (CIP) rules 1 and 2 (material differences) have been expressed in the formal logic of a high‐level computer language (FORTRAN IV) on a laboratory minicomputer (PDP 11/40) by the program CHIRAL. An oversight in the CIP formalism in the treatment of rings was treated on anad hocbasis; the problem has been expressed simply in terms of elementary graph theory in a way consistent with and similar to chemical notation. An example of the operation of CHIRAL is provided and the internal procedu

ISSN:0192-8651    

DOI:10.1002/jcc.540010303

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractMINDO/3 calculations have been carried out for a series of branched chain alkanes in order to assess effects of branching on calculated geometries and heats of formation (ΔHf). With vicinal branching, MINDO/3 calculates the central CC bond to be too long. Bond angles are also found to be distorted. Errors in calculated heats of formation are large when geminal branching is present and significant with vicinal branching. Branching error corrections for ΔHfhave been derived and applied to a separate series of branched acyclic and cyclic compounds. For the test sample, application of the branching error corrections gave calculated structures of acyclic branched hydrocarbons with heats of formation having an average absolute error of 1.3 kcal/mole rather than 17.3 kcal/mole before correction. Cyclic branched hydrocarbons are shown to be less well corrected. Calculations of heats of reaction have also been carried out for some isomerization and cyclization reactions using the MINDO/3 and MNDO methods. It is clear from the comparisons that MNDO calculations give less severe errors for highly branched compounds but the errors are still substantial. For prediction of heats of reaction, the error‐corrected calculations are shown to be superior to the “raw” calculations obtained by MINDO/

ISSN:0192-8651    

DOI:10.1002/jcc.540010304

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe optical activity of conjugated dienes is investigated by means ofab initioSCF–CI calculations. The computed electronic spectrum oftrans‐1,3‐butadiene is shown to be in good agreement with the results of more rigorous calculations of the valence transitions and in satisfactory agreement with experiment. The optical rotatory strengths of the lower electronic transitions of twisted 1,3‐butadiene as a function of dihedral angle are presented and simulated CD spectra are produced. TheN→V1(π2→ π3*) transition is predicted to have a positive rotational strength for all dihedral angles that correspond to a right‐handed twist of the chromophore, in accord with the empirically deduced “diene rule” although for a twist angle of 60°, the rotatory strength is calculated to be almost zero. The role of the orientation of allylic bonds is investigated in the model system 1‐butene in which the rotational strength of the π → π* transition as a function of rotation about the 2,3 bond is determined. The effect of allylic bond disposition in dienes on the optical activity of the long‐wavelength π2→ π3* transition is simulated by use of the exciton coupling model of Harada and Nakanishi in which two 1‐butene molecules with suitable geometries are coupled via interactions of the electric dipole transition moments of their π → π* transitions. The model systems 1,3‐butadiene and 1‐butene are used to rationalize the apparently anomalous optical activity of (−)‐α‐phellandrene and (−)‐β‐phellandrene, both of which should have a diene chromophore with a right‐handed twist in their most stable conformers and so should be dextrorotatory. The experimental CD spectrum of α‐phellandrene is determined at several temperatures down to −180°C. The observed variation of the apparent rotational strength of theN→V1transition is in good

ISSN:0192-8651    

DOI:10.1002/jcc.540010305

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractGraphite is the limiting case of an infinite aromatic hydrocarbon, and as such is an important benchmark in force‐field calculations. Using experimentally determined physical properties for graphite, a force‐field parameter set was developed for molecular mechanics calculations with unsaturated hydrocarbons and is described and discus

ISSN:0192-8651    

DOI:10.1002/jcc.540010306

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractA molecular packing analysis of the hydrogen‐bonded layer structure of maleic hydrazide shows that even in such a structure, the van der Waals energy is the dominant component of the lattice energy. The hydrogen‐bond energy of the observed structure is greater than that for alternative structures based on a different mode of hydrogen bonding, and this makes the observed more sta

ISSN:0192-8651    

DOI:10.1002/jcc.540010307

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractTwo algorithms for the local energy minimization of the structure of macromolecules in the presence of constraints are proposed. They are a combination of the method of steepest descents and the method of conjugate gradients with the procedure SHAKE, by which distance constraints can be satisfied. The two algorithms are tested by applying them to a small protein, the bovine pancreatic trypsin inhibitor (BPTI), and compared with the penalty function method for conserving constraints. The efficiency of the proposed methods depends on the level of interdependence of the constraints. For bond‐length constraints, the use of SHAKE is superior to the penalty function method. However, when bond‐angle constraints are included, SHAKE is more efficient only if the curvature of the penalty function is considerably greater than that of the potential function being minimized. The results indicate that with bond‐length constraints the minimization behavior is similar to that without constraints. However, the simultaneous application of bond‐length and bond‐angle constraints appears to confine the molecule to a very limited part of configuration space, very different from the part covered by an unconstrained minimization. This conclusion calls into question energy minimizations of protein systems in which only the dihedral angles are allowe

ISSN:0192-8651    

DOI:10.1002/jcc.540010308

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe results ofab initio“supermolecule” calculations of the charge transfer between formamide and methylglyoxal, ethylglyoxal, and dimethylglyoxal are compared for several different relative conformations of the constituent molecules. The charge transfer properties of ethylglyoxal were found to be quite different to those of the other two glyox

ISSN:0192-8651    

DOI:10.1002/jcc.540010309

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractCalculations at the STO‐3G and 4–31G levels have been carried out on propylamine and ethylmethylamine, using geometries determined by molecular mechanics by allowing complete molecular relaxation in all degrees of freedom except for torsion about the central bond, and at 30° increments for the latter. It was found that a butanelike potential exists in each case. From 0° (cis) to 360° in order, the 4–31G values for the energy extrema are 5.92, 0.12, 3.88, 0.00, 3.94, and 0.51 kcal/mole for propylamine (with the nitrogen lone pairgaucheto carbon), and 7.06, 1.45, 3.44, 0.0, 2.87, and 1.44 kcal/mole for ethylmet

ISSN:0192-8651    

DOI:10.1002/jcc.540010310

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractCalculations at the STO‐3G and 4–31G levels have been carried out on propanol and ethyl methyl ether, with geometries obtained from molecular mechanics calcualations. Full relaxation was allowed in all degrees of freedom except for the torsion about the central bond, which was varied at 30° increments. A butane‐type potential was found, the maximum and minimum values of energy are from 0° to 180° 5.55, 0.00, 4.02, and 0.00 kcal/mole for propanol, and 8.35, 2.74, 3.31, and 0.00 kcal/mole for ethyl methyl ether

ISSN:0192-8651    

DOI:10.1002/jcc.540010311

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY