Why Benchmark-Quality Computations Are Needed To Reproduce 1-Adamantyl Cation NMR Chemical Shifts Accurately

Harding, Michael E.; Gauß, Jürgen; Schleyer, Paul von Ragué

doi:10.1021/jp1103356

Cited by 23 publications

(58 citation statements)

References 58 publications

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“…For obtaining improved energy values, MP4-(SDTQ)/cc-pVQZ calculations on MP2/cc-pVQZ geometries were carried out. 13 C NMR chemical shifts were calculated by the GIAO (gauge invariant atomic orbitals) method 31 using different geometries. CCSD(T)/cc-pVTZ optimizations and GIAO-CCSD(T), GIAO-MP2, and GIAO-SCF calculations using tzp (carbon)/dz (hydrogen) and qzp (carbon)/tzp (hydrogen) basis sets, which were optimized by Schafer, Horn, and Ahlrichs 32,33 have been performed with the CFOUR program.…”

Section: ■ Calculationsmentioning

confidence: 99%

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MP2, CCSD(T), and Density Functional Theory Study of the 2-Butyl Cation: New Insight into the Methyl- and Hydrogen-Bridged Structures

2015

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Using the MP2, CCSD(T), and DFT (B3LYP) methods, the structures and energies of the 2-butyl cation (C4H9(+)) were calculated. Energetically, the C-C hyperconjugated structure 1 and hydrogen-bridged structure 2 were found to be almost identical at all levels. The (13)C NMR chemical shifts of 1 and 2 were computed by the GIAO-CCSD(T) method using different geometries. On the basis of calculated relative energies and calculated (13)C NMR chemical shifts, an equilibrium involving 1 and 2 (in a 50:50 ratio) seemed likely responsible for the experimentally observed (13)C NMR chemical shifts in superacid solutions at -80 °C. However, on the basis of computed and experimental frequencies the hydrogen-bridged structure 2 is most likely responsible for the experimentally observed frequencies in the solid state at -125 °C.

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Section: ■ Calculationsmentioning

confidence: 99%

“…An initial 13 C NMR INDOR spectrum of i was obtained by Olah and White, 4 which showed a single peak from the two central carbon atoms. This was in reasonable agreement with values calculated from model equilibrating trivalent cations undergoing rapid 1,2-hydrogen shifts.…”

Section: ■ Introductionmentioning

confidence: 99%

MP2, CCSD(T), and Density Functional Theory Study of the 2-Butyl Cation: New Insight into the Methyl- and Hydrogen-Bridged Structures

2015

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“…In the relaxed form this cation has a near planar geometry for the C1 as has been established by Harding et al on the basis of 13C NMR data combined with sophisticated calculations [16]. Geometry calculations have been performed by Rasul et al for this cation [17].…”

Section: Ab Initio and Van't Hoff Modelling For A Planar Trivalent Camentioning

confidence: 83%

Interconversion between Planar-Triangle, Trigonal-Pyramid and Tetrahedral Configurations of Boron (B(OH)3 -B(OH)4- ), Carbon (CH3+ -CH3X) and for the Group 15 Elements as Nitrogen (NH3-NH4<sup

Buck¹

2015

OJPC

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“…62 The chemical shifts of 1-adamantyl cation were computed at B3LYP/def2-QZVPP and MP2/qz2p//MP2/cc-pVTZ. Harding et al take on the interesting spectrum of 1-adamantyl cation to try to discern the important factors in computing its 13 C and 1 H chemical shifts.…”

Section: -Adamantyl Cationmentioning

confidence: 99%

Computed Spectral Properties and Structure Identification

Bachrach

2014

Computational Organic Chemistry

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Once the wavefunction is in hand, all observable properties can, at least in principle, be computed. This can include all varieties of spectral properties, which are particularly valuable in ascertaining molecular structure. The full theoretical and computational means for computing spectral properties are mathematically involved and beyond the scope of this chapter. Instead, we will focus on the use of quantum chemical computations to help identify chemical structure. The purpose of this chapter is to inspire the routine use of computed spectra to aid in structural identification.As discussed in Chapter 1, the full three-dimensional structure of a compound can be optimized with almost any of the quantum computational techniques. Since most quantum chemical computations are still performed on a single molecule in the gas phase, these computed structures can be most readily compared to gas-phase experimental structures. In the following chapters, we will present a number of case studies where computed and experimental geometries are compared. To get a sense of the quality of computed geometries, a few selected cases are discussed next. COMPUTED BOND LENGTHS AND ANGLESSchaefer and Allinger 1 examined a series of small organic compounds with a number of different computational methods. Table 2.1 compares the C-C and C-H bond lengths (r e ) in some very small compounds, and finds the coupled-cluster singles and doubles (CCSD/TZ2+P) results in excellent agreement with the limited experimental values. Importantly, the bond lengths predicted by the much more computationally efficient B3LYP/6-31G* are very similar to the CCSD results. For a group of 10 small hydrocarbons, including some alkenes and alkynes, the B3LYP/6-31G* C-C and C-H distances are on an average too small (compared with r g values) by only 0.0031 and 0.016 Å, respectively. Similar excellent performance is also seen for a group of 19 organic compounds containing oxygen or nitrogen.

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Why Benchmark-Quality Computations Are Needed To Reproduce 1-Adamantyl Cation NMR Chemical Shifts Accurately

Cited by 23 publications

References 58 publications

MP2, CCSD(T), and Density Functional Theory Study of the 2-Butyl Cation: New Insight into the Methyl- and Hydrogen-Bridged Structures

MP2, CCSD(T), and Density Functional Theory Study of the 2-Butyl Cation: New Insight into the Methyl- and Hydrogen-Bridged Structures

Interconversion between Planar-Triangle, Trigonal-Pyramid and Tetrahedral Configurations of Boron (B(OH)<sub>3</sub> -B(OH)<sub>4</sub><sup>-</sup> ), Carbon (CH<sub>3</sub><sup>+</sup> -CH<sub>3</sub>X) and for the Group 15 Elements as Nitrogen (NH<sub>3</sub>-NH<sub>4</sub><sup

Computed Spectral Properties and Structure Identification

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