Abstract Atomic charges were obtained from ab initio molecular orbital calculations using a variety of procedures to compare them and assess their utility. Two based on the orbitals examined, Mulliken population analysis Weinhold–Reed Natural Population Analysis. charge density distribution included; Hirshfeld procedure Bader's Atoms in Molecules method. Charges also derived by fitting electrostatic potential (CHELPG) making use atomic polar tensors (GAPT). The first examined for basis set...

Hydrogen bonding between water and a series of small organic molecules was examined via electronic structure calculations. Several computational methods were examined, including both hybrid density functional procedure (Becke3LYP) second-order Møller−Plesset theory (MP2) coupled with double-ζ basis set augmented by diffuse polarization functions on heteroatoms. The agreement Becke3LYP MP2 energies generally good, as the obtained using more sophisticated costly methods. structures 53...

The purpose of this paper is to convince practitioners (1)H NMR spectroscopy consider simple quantum chemical calculations as a viable option aid them in the assignment their spectra. To end, it demonstrated, on test set 80 conformationally stable molecules various kinds carrying different functional groups, that, contrast what claimed literature, large basis sets are not needed obtain rather accurate predictions shifts by calculations. On other hand, modeling solvent an SCRF-type...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAmides. 3. Experimental and Theoretical Studies of the Effect Medium on Rotational Barriers for N,N-Dimethylformamide N,N-DimethylacetamideKenneth B. Wiberg, Paul R. Rablen, Daniel J. Rush, Todd A. KeithCite this: Am. Chem. Soc. 1995, 117, 15, 4261–4270Publication Date (Print):April 1, 1995Publication History Published online1 May 2002Published inissue 1 April...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTWhy Does Thioformamide Have a Larger Rotational Barrier Than Formamide?Kenneth B. Wiberg and Paul R. RablenCite this: J. Am. Chem. Soc. 1995, 117, 8, 2201–2209Publication Date (Print):March 1, 1995Publication History Published online1 May 2002Published inissue 1 March 1995https://pubs.acs.org/doi/10.1021/ja00113a009https://doi.org/10.1021/ja00113a009research-articleACS PublicationsRequest reuse permissionsArticle...

Fifteen procedures based on hybrid density functional theory were used to calculate magnetic properties for the carbon-bound hydrogen nuclei of 80 small modest-sized organic molecules. The predicted isotropic shieldings derived from various methods compared with each other and also solution experimental data. computational investigated included IGAIM GIAO procedures, 6-311++G(d,p), 6-311++G(2df,p), 6-311++G(3df,2p) basis sets, B3LYP, B3P86, B3PW91 functionals, molecular geometries optimized...

N-methyl mesoporphyrin IX (NMM) is exceptionally selective for G-quadruplexes (GQ) relative to duplex DNA and, as such, has found a wide range of applications in biology and chemistry. In addition, NMM parallel versus antiparallel GQ folds, was recently demonstrated our laboratory. Here, we present the X-ray crystal structure complex between human telomeric dAGGG(TTAGGG)(3), Tel22, determined two space groups, P2(1)2(1)2 P6, at 1.65 2.15 Å resolution, respectively. The former highest...

The performance of 250 different computational protocols (combinations density functionals, basis sets and methods) was assessed on a set 165 well-established experimental (1)H-(1)H nuclear coupling constants (J(H-H)) from 65 molecules spanning wide range "chemical space". Thereby we found that, if one uses core-augmented allows for linear scaling the raw results, calculations only Fermi contact term yield more accurate predictions than where all four terms that contribute to J(H-H) are...

We report the first reductive coupling of unactivated alkenes with N-methoxy pyridazinium, imidazolium, quinolinium, and isoquinolinium salts under hydrogen atom transfer (HAT) conditions, an expanded scope for pyridinium salts. N-Methoxy are accessible in 1–2 steps from commercial arenes or arene N-oxides (25–99%). imidazolium three amines (50–85%). In total 36 discrete methoxyheteroarenium bearing electron-donating, electron-withdrawing, alkyl, aryl, halogen, haloalkyl substituents were...

The problem of deriving atomic charges from the results ab Initio MO calculations has been studied by use several reported methods: Mulliken population analysis, minimal basis set (MBS) procedure, natural analysis (NPA), two electrostatic potential fitting methods, M-K and ChelpG, Hirshfeld CM5 (charge model 5), which is related to method. first studies were concerned with hydrogen charges. It was found that MBS linearly Hirshfeld, CM5, but not others, provided an excellent correlation for H...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSubstituent effects. 4. Nature of substituent effects at carbonyl groupsKenneth B. Wiberg, Christopher M. Hadad, Paul R. Rablen, and Jerzy CioslowskiCite this: J. Am. Chem. Soc. 1992, 114, 22, 8644–8654Publication Date (Print):October 1, 1992Publication History Published online1 May 2002Published inissue 1 October 1992https://pubs.acs.org/doi/10.1021/ja00048a044https://doi.org/10.1021/ja00048a044research-articleACS PublicationsRequest reuse...

Ab initio molecular orbital calculations at the G-2 and CBS-4 compound levels of theory were used to determine sequential homolytic bond dissociation energies (BDE's) for a series B−H, B−C, B−F bonds in variety cyclic acyclic boranes. The calculated average BDE's agreed very well with limited experimental data available. However, first BDE's, which are most relevant understanding borane reactivity, substantially higher than BDE's. In general, found be larger B−C B−H organoboranes C−C C−H...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOrigin of the stability carbon tetrafluoride: negative hyperconjugation reexaminedKenneth B. Wiberg and Paul R. RablenCite this: J. Am. Chem. Soc. 1993, 115, 2, 614–625Publication Date (Print):January 1, 1993Publication History Published online1 May 2002Published inissue 1 January 1993https://pubs.acs.org/doi/10.1021/ja00055a034https://doi.org/10.1021/ja00055a034research-articleACS PublicationsRequest reuse permissionsArticle...

Ab initio molecular orbital calculations at the G-2 and CBS-4 levels of theory were used to determine homolytic bond dissociation energies (BDE's) for B−H bonds in a series donor−acceptor complexes borane. The four-coordinate boron found be weaker than those three-coordinate boron. effect complexation on BDE varied from very small, cases NH3 H2O, as much 30−50 kcal/mol, formaldehyde, CO, HCN. BDE's not correlate with strength coordination. However, they closely correlated degree which spin...

The energies and geometries of a series 2-substituted-1-fluoroethanes were computed at the MP2/6-311++G**(6D)//MP2/6-31+G* level theory for both maxima minima rotation about C–C bond. results did not support predictions hyperconjugative model, that 1,2-difluoroethane 1-chloro-2-fluoroethane would strongly prefer gauche conformation, 1-fluoro-2-silylethane an anti conformation. existence competing electrostatic interactions between fluorine substituents C-2 was indicated by detailed...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTResonance interactions in acyclic systems. 5. Structures, charge distributions, and energies of some heterobutadiene rotamersKenneth B. Wiberg, Paul R. Rablen, Manuel MarquezCite this: J. Am. Chem. Soc. 1992, 114, 22, 8654–8668Publication Date (Print):October 1, 1992Publication History Published online1 May 2002Published inissue 1 October 1992https://doi.org/10.1021/ja00048a045Request reuse permissionsArticle Views142Altmetric-Citations70LEARN...

The addition of N-methylimidazole (NMI) to the reaction homophthalic anhydride with imines such as pyridine-3-carboxaldehyde-N-trifluoroethylimine (9) reduces amount elimination byproduct and improves yield formal cycloadduct, tetrahydroisoquinolonic carboxylate 10. Carboxanilides compounds are interest potential antimalarial agents. A mechanism that rationalizes role NMI is proposed, a gram-scale procedure for synthesis resolution 10 also described.

High-level electronic structure calculations, including a continuum treatment of solvent, are employed to elucidate and quantify the effects alkyl halide on barriers SN2 E2 reactions. In cases where such comparisons available, results these calculations show close agreement with solution experimental data. Structural factors investigated include α- β-methylation, adjacency unsaturated functionality (allyl, benzyl, propargyl, α carbonyl), ring size, α-halogenation cyanation. While influence...

A method is presented for the direct computation of hydrocarbon strain energies using computational group equivalents. Parameters are provided at several high levels electronic structure theory: W1BD, G-4, CBS-APNO, CBS-QB3, and M062X/6-31+G(2df,p). As an illustration procedure, computed 66 hydrocarbons, most them highly strained.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTImportance of Polarization for Dipolar Solutes in Low-Dielectric Media: 1,2-Dichloroethane and Water CyclohexaneWilliam L. Jorgensen, Nora A. McDonald, Massimo Selmi, Paul R. RablenCite this: J. Am. Chem. Soc. 1995, 117, 47, 11809–11810Publication Date (Print):November 1, 1995Publication History Published online1 May 2002Published inissue 1 November...

Using ab initio MO theory, a series of isodesmic reactions was studied in which nitrogen-, oxygen-, and fluorine-containing species acted as proton donors acceptors. Comparison protonation deprotonation energies suggests that approximately three-quarters the enhanced acidity acetic acid comes from electrostatic stabilization, while remaining quarter results π resonance. Similar logic shows only one-third nitrogen analogue acetamidine is nature, two-thirds derives The primary importance...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFirst Transition Metal-Boryl Bond Energy and Quantitation of Large Differences in Sequential Dissociation Energies BoranesPaul R. Rablen, John F. Hartwig, Steven P. NolanCite this: J. Am. Chem. Soc. 1994, 116, 9, 4121–4122Publication Date (Print):May 1, 1994Publication History Published online1 May 2002Published inissue 1 1994https://pubs.acs.org/doi/10.1021/ja00088a075https://doi.org/10.1021/ja00088a075research-articleACS PublicationsRequest reuse...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAddition of Catecholborane to a Ruthenium-Alkyl: Evidence for .sigma.-Bond Metathesis with Low-Valent, Late Transition MetalJohn F. Hartwig, Sonali Bhandari, and Paul R. RablenCite this: J. Am. Chem. Soc. 1994, 116, 5, 1839–1844Publication Date (Print):March 1, 1994Publication History Published online1 May 2002Published inissue 1 March 1994https://pubs.acs.org/doi/10.1021/ja00084a027https://doi.org/10.1021/ja00084a027research-articleACS...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSubstituent effects. 5. Vinyl and ethynyl derivatives. An examination of the interaction amino hydroxy groups with carbon-carbon double triple bondsKenneth B. Wiberg Paul R. RablenCite this: J. Am. Chem. Soc. 1993, 115, 20, 9234–9242Publication Date (Print):October 1, 1993Publication History Published online1 May 2002Published inissue 1 October 1993https://doi.org/10.1021/ja00073a044RIGHTS & PERMISSIONSArticle Views293Altmetric-Citations56LEARN...