Dynamic NMR and molecular mechanics study of the rotation of a 1-adamantyl, a 1-bicyclooctyl, a 1-norbornyl, and a tert-butyl group. The relative size of an adamantyl group. The dilemma of calculated barriers to rotation

Anderson, J. Edgar; Pearson, Harry; Rawson, D. I.

doi:10.1021/ja00291a075

Cited by 16 publications

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“…These include 2-chloro-2-methylbutane, 10b 1-chloro-2,2-dimethylpropane, 10a 2-chloro-2,3-dimethylbutane, 32 2-chloro-3,3-dimethylbutane, 10a 2-chloro-2,3,3-trimethylbutane, 33 3-chloro-2,2,3-trimethylpentane, 34 3-chloro-2,2,3,4,4-pentamethylpentane, 33 3-chloro-2,2,3,5,5-pentamethylhexane, 33 2-bicyclo[2.2.2]octyl-2-chloropropane, 35 and 2-adamantyl-2-chloro-3,3-dimethylbutane. 35 The results are summarized in Table 3. In general, the results are fairly good (at most less than 2 kcal/mol difference).…”

Section: Resultsmentioning

confidence: 99%

Molecular Mechanics (MM3) Conformational Studies of Cyclic and Acyclic Monochloroalkanes

1996

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Molecular mechanics calculations play an important role in modern conformational analysis. Alkyl chlorides are useful organic compounds that have been used as important intermediates and target compounds of commercial and academic interest. Molecular modeling studies utilizing force field calculations have become very popular in the past decade, but in order to make quantitative predictions of unknown compounds it is critical to be able to calculate accurately the energy among conformational equilibrium structures and transition state barriers for known compounds of the same family. An MM3 force field for monochloroalkanes has been developed recently that accurately reproduces molecular structures and vibrational frequencies. This paper presents and compares MM3 calculations with experimental data (Raman, IR, ED, MW, and NMR) for selected cyclic and acyclic monochlorohydrocarbons.

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Section: Resultsmentioning

confidence: 99%

Molecular Mechanics (MM3) Conformational Studies of Cyclic and Acyclic Monochloroalkanes

1996

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“…Similarly, the comparison between 2 (9.3 kcal mol −1 ) and bond a in 4 (12.2 kcal mol −1 ) clearly shows that by increasing the size of the alkyl groups, the bond rotational barrier increases. However, as shown and interpreted by E. Anderson, besides bulkiness, flexibility can be an equally significant factor in single bond rotational barriers. Specifically, Csp 3 ‐Csp 3 energy barriers were found lower than expected when one Csp 3 is part of the bulky but rigid 1‐adamantyl group, compared to when ist part of the smaller but flexible tert ‐butyl group.…”

Section: Resultsmentioning

confidence: 85%

“…In Table , the energy barriers for Csp 3 ‐Csp 3 bond rotation in previously studied compounds 1–10 using DNMR are included for comparison, considering that the activation entropy changes are similar or approximately zero for all compounds . This is usual in the majority of conformational processes investigated by DNMR; indeed, in the case of compound 11 activation entropy was found to be only 0.2 kcal mol −1 (see Eyring plot in Figure S2).…”

Section: Resultsmentioning

confidence: 99%

“…Three decades ago, in a pioneering work E. Anderson studied the relative impact of tert ‐butyl group and 1‐adamantyl group, when they reside at the one end of a Csp 3 ‐Csp 3 bond e.g. in tBuCMe 2 Cl ( 1 ) and AdCMe 2 Cl ( 2 ) . In the present work, we examined the barrier for 1‐Ad‐Csp 3 bond rotation in AdCEt 2 OH ( 11 ) and AdCEt 2 Cl ( 12 ) using DNMR.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, we utilized adamantane derivatives as conformational models of cyclohexane derivatives and conducted weak forces investigation . The experimental values of Csp 3 ‐Csp 3 bond rotational energy barriers of groups such as tert ‐butyl, 1‐ or 2‐adamantyl, and other structures are significant for the fundamentals of conformational analysis and the evaluation of force field parameters. Three decades ago, in a pioneering work E. Anderson studied the relative impact of tert ‐butyl group and 1‐adamantyl group, when they reside at the one end of a Csp 3 ‐Csp 3 bond e.g.…”

Section: Introductionmentioning

confidence: 99%

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Rotation Barriers of 1‐Adamantyl‐Csp³ Bonds Measured with Dynamic NMR

et al. 2019

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Adamantane is a lipophilic symmetrical hydrocarbon cage, which has been successfully used as a valuable fragment in drug design. The bond rotations of the 1-adamantyl group in Ad-CEt 2 OH (11) and Ad-CEt 2 Cl (12) were investigated, and the bond rotation barriers were compared with energy values from similar compounds measured previously. Exchange rate constants were estimated from lineshape fitting of low temperature 13 C NMR data for compound 11, and used to estimate the free energy of the 1-adamantyl group's single bond rotation at 8.8 kcal mol À 1 . Spectra analyses for compound 12 were hampered by impurities, and only an estimate of the respective rate constant was possible from a single coalescence point. The free energy for bond rotation of 1-adamantyl group in 12 was found to be ∼ 10 kcal mol À 1 , based on decoalescence of signals at À 100 ο C. The barrier for 12 is comparable with the single bond rotation barrier of Ad-CMe 2 Cl (2) (9.3 kcal mol À 1 ), or the analogous barrier of tBu-CMe 2 Cl (1) (10.4 kcal mol À 1 ). As previously suggested, single bond rotational barriers Csp 3 -Csp 3 were found lower than expected when one Csp 3 is included in a bulky but rigid tertiary residue (e. g. 1-adamantyl), compared to a smaller but more flexible residue (e. g. tert-butyl).

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Rotational barriers of disilane, hexafluorodisilane, and hexamethyldisilane:Ab initio, density functional, and molecular mechanics (MM3) studies

1997

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We investigated structures, vibrational frequencies, and rotational barriers of disilane (Si2H6), hexafluorodisilane (Si2F6), and hexamethyldisilane (Si2Me6) by using ab initio molecular orbital and density functional theories. We employed four different levels of theories (i.e., HF/6–31G*, MP2/6–31G*, BLYP/6–31G*, and B3LYP/6–31G*) to optimize the structures and to calculate the vibrational frequencies (except for Si2Me6 at MP2/6–31G*). MP2/6–31G* calculations reproduce experimental bond lengths well, while BLYP/6–31G* calculations largely overestimate some bond lengths. Vibrational frequencies from density functional theories (BLYP/6–31G* and B3LYP/6–31G*) were in reasonably good agreement with experimental values without employing additional correction factors. We calculated the ΔG‡(298 K) values of the internal rotation by correcting zero‐point vibration energies, thermal vibration energies, and entropies. We performed CISD/6–31G*//MP2/6–31G* calculations and found the ΔG‡(298 K) values for the internal rotation of Si2H6, Si2F6, and Si2Me6 to be 1.36, 2.06, and 2.69 kcal/mol, respectively. The performance of this level was verified by using G2 and G2(MP2) methods in Si2H6. According to our theoretical results, the ΔG‡(298 K) values were marginally greater than the ΔE‡(0 K) values in Si2F6 and Si2Me6 due to the contribution of the entropy. In Si2H6 the ΔE‡(0 K) and ΔG‡(298 K) values were coincidently similar due to a cancellation of two opposing contributions between zero‐point and thermal vibrational energies, and entropies. Our calculated ΔG‡(298 K) values were in good agreement with experimental values published recently. In addition, we also performed MM3 calculations on Si2H6 and Si2Me6. MM3 calculated rotational barriers and thermodynamic properties were compared with high level ab initio results. Based on this comparison, MM3 calculations reproduced high level ab initio results in rotational barriers and thermodynamic properties of Si2H6 derivatives including vibrational energies and entropies, although large errors exist in some vibrational frequencies. © 1997 John Wiley & Sons, Inc. J Comput Chem 18: 1523–1533, 1997

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Dynamic NMR and molecular mechanics study of the rotation of a 1-adamantyl, a 1-bicyclooctyl, a 1-norbornyl, and a tert-butyl group. The relative size of an adamantyl group. The dilemma of calculated barriers to rotation

Cited by 16 publications

References 0 publications

Molecular Mechanics (MM3) Conformational Studies of Cyclic and Acyclic Monochloroalkanes

Molecular Mechanics (MM3) Conformational Studies of Cyclic and Acyclic Monochloroalkanes

Rotation Barriers of 1‐Adamantyl‐Csp³ Bonds Measured with Dynamic NMR

Rotational barriers of disilane, hexafluorodisilane, and hexamethyldisilane:Ab initio, density functional, and molecular mechanics (MM3) studies

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Dynamic NMR and molecular mechanics study of the rotation of a 1-adamantyl, a 1-bicyclooctyl, a 1-norbornyl, and a tert-butyl group. The relative size of an adamantyl group. The dilemma of calculated barriers to rotation

Cited by 16 publications

References 0 publications

Molecular Mechanics (MM3) Conformational Studies of Cyclic and Acyclic Monochloroalkanes

Molecular Mechanics (MM3) Conformational Studies of Cyclic and Acyclic Monochloroalkanes

Rotation Barriers of 1‐Adamantyl‐Csp3 Bonds Measured with Dynamic NMR

Rotational barriers of disilane, hexafluorodisilane, and hexamethyldisilane:Ab initio, density functional, and molecular mechanics (MM3) studies

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Rotation Barriers of 1‐Adamantyl‐Csp³ Bonds Measured with Dynamic NMR