NMR isotope shift and perturbational MO study of conformation and hyperconjugation in cyclopentyl cations

Botkin, J. H.; Forsyth, David; Sardella, D. J.

doi:10.1021/ja00271a001

Cited by 10 publications

(6 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…7 kcal/mol at the B3LYP/6-31G(d) level) than for the hydride migration from the C1 to C2 carbon atom. This is in accord with the experimental findings of Forsyth, who showed that the hydride migration on the cyclopentyl ring in the tetradeuterated 1-methyl-1-cyclopentyl cation occurs at temperature above −80 °C and is slow on the NMR time scale.…”

Section: Resultssupporting

confidence: 92%

Rearrangement Pathways of Five-Membered Ring Enlargement in Carbocations: Quantum Chemical Calculations and Deuterium Kinetic Isotope Effects

2003

View full text Add to dashboard Cite

Three plausible routes for the five-membered ring expansion in the equilibrating 2-cyclopentyl-2-propyl and 1-(2-propyl)cyclopentyl cations 1A/1B were located on the PES, all calculated at the MP4/6-31G(d)//MP2/6-31G(d) level of theory. In pathway I, the six-membered transition structure (TS-I) connects the less stable cyclopentyl cation 1A and the 1,2-dimethylcyclohexyl carbocation (2) via a barrier of 16.4 kcal/mol. In pathway II, which has a barrier of 16.3 kcal/mol, the methyl migration occurs first in the more stable 1B via transition structure TS-II. Pathway III involves the uphill hydride shift and formation of the secondary cation 3, which undergoes Wagner-Meerwein 1,2-isopropyl shift via a transition structure TS-III and the protonated carbocation intermediate 4. The barrier pathway III is for 17.0 kcal/mol. Experimental secondary deuterium isotope effects of the rearrangement were measured for the hexadeuterated 1A-d6/1B-d6 (kH/kD = 2.40) and tetradeuterated 1A-d4/1B-d4 (kH/kD = 0.18) cations by means of 1H NMR. Comparison of the experimental data with the theoretical values (kH/kD = 2.40 for 1B-d6 and kH/kD = 0.24 for 1B-d4, respectively) obtained with QUIVER revealed that pathway II is a major reaction route.

show abstract

Section: Resultssupporting

confidence: 92%

Rearrangement Pathways of Five-Membered Ring Enlargement in Carbocations: Quantum Chemical Calculations and Deuterium Kinetic Isotope Effects

2003

View full text Add to dashboard Cite

show abstract

“…2) with the 2pπ orbital at the carbon C1Ј as compared to the other vicinal cyclopentyl bond (d(C1-C2) = 1.539 or 1.520 Å; at B3LYP/6-31G(d) or MP2/6-31G(d) level of theory). Even more pronounced is the variance of the two bond angles C1Ј-C1-C5 (95.8 and 82.2Њ) and C1Ј-C1-C2 (123. and CHD-deuterated isotopomers of the 1-methylcyclopentyl cation 12 and is also in accord with ab initio calculations for the twisted conformation of the parent cyclopentyl cation. 13 The cyclopentyl cation 1B is calculated to be 1.…”

Section: The 2-cyclopentyl-2-propyl Cation (1a) 1-(2-propyl)cyclopent...supporting

confidence: 80%

Nondegenerate equilibrium in (2-propyl)cycloalkyl cations. Comparison of (2-propyl)cyclopentyl and (2-propyl)cyclohexyl cation using 13C NMR spectroscopy, equilibrium isotope effects and quantum chemical calculationsElectronic supplementary information (ESI) available: redundant coordinates for structures 1A, 1B, 1TS, 2A, 2B1, 2B2 and 2TS; van't Hoff plot for equilibrium 1A ⇋ 1B. See http://www.rsc.org/suppdata/p2/b1/b107756b/

Siehl

Vrek

Kronja

2001

J. Chem. Soc., Perkin Trans. 2

View full text Add to dashboard Cite

“…l6 in ESR,"-" UPS,2o CT,,l*,, and W B spectroscopy. Recently importance of hyperconjugation on NMR spectroscopy was pointed out by Botkin et al, 24 Emst et al, 25 Brown and Periasamy, 26 Siehl and Walteqn and Olah et al 14 However, their studies do not concern the hyperconjugation in solid-state NMR spectroscopy, with which our study is concerned, but, from their success in dealing with it, our study must be reasonable concerning the use of the concept.…”

Section: Resultsmentioning

confidence: 73%

A solid state NMR study on crystalline forms of nylon 6

Okada

Kawasumi

Tajima

et al. 1989

J of Applied Polymer Sci

View full text Add to dashboard Cite

SynopsisHigh-resolution 13C-NMR spectra were studied for two different crystalline structures of nylon 6 in the solid state by the crass polarization/magic angle spinning (CP/MAS) method. Two crystalline structures, a-form and y-form, gave different chemical shifts for methylene carbons. The results showed that the hydrogen bonds between intermolecular chains are stronger in the y-form than in the a-form. This strongly supports the results of the X-ray study of nylon 6 by Malta et al. Our results also showed that intramolecular delocalization of positive charges occurs in the y-form through hyperconjugation in which the dihedral angle between the I bond and neighboring a bonds is 3 0 ' while no such effect can be expected in the a-form in which the angle is 0".

show abstract

NMR isotope shift and perturbational MO study of conformation and hyperconjugation in cyclopentyl cations

Cited by 10 publications

References 7 publications

Rearrangement Pathways of Five-Membered Ring Enlargement in Carbocations: Quantum Chemical Calculations and Deuterium Kinetic Isotope Effects

Rearrangement Pathways of Five-Membered Ring Enlargement in Carbocations: Quantum Chemical Calculations and Deuterium Kinetic Isotope Effects

A solid state NMR study on crystalline forms of nylon 6

Contact Info

Product

Resources

About