Investigation of the internal rotation of methyl groups by T1 relaxation measurements

1978 ◽  
Vol 31 (1) ◽  
pp. 33-40 ◽  
Author(s):  
E Haslinger ◽  
R.M Lynden-Bell
Keyword(s):  
Internal Rotation ◽  
Methyl Groups ◽  
T1 Relaxation ◽  
Relaxation Measurements

scholarly journals 23Na NMR T1 relaxation measurements as a probe for diffusion and dynamics of sodium ions in salt–glycerol mixtures

2021 ◽  
Vol 154 (22) ◽  
pp. 224501
Author(s):  
Carmine D’Agostino ◽  
Stefan J. Davis ◽  
Andrew P. Abbott
Keyword(s):  
Sodium Ions ◽  
T1 Relaxation ◽  
Relaxation Measurements ◽  
23Na Nmr

The Microwave Spectrum of 2,6-Lutidine, Analysis of Internal Rotation and 14 N Hyperfine Structure

1993 ◽  
Vol 48 (11) ◽  
pp. 1093-1101 ◽  
Author(s):  
C. Thomsen ◽  
H. Dreizler
Keyword(s):  
Fourier Transform ◽  
Hyperfine Structure ◽  
Internal Rotation ◽  
Molecular Beam ◽  
Microwave Spectrum ◽  
Methyl Groups ◽  
Rotational Spectrum ◽  
Rotational Constants ◽  
Moments Of Inertia ◽  
Nuclear Quadrupole

Abstract The rotational spectrum of 2,6-lutidine, (CH3)2C5H3N, has been recorded between 6 and 26.5 GHz using pulsed molecular beam microwave Fourier transform spectroscopy. The rotational constants are A = 3509.7139(84) MHz, B = 1906.8639(101) MHz, and C = 1254.6215(14) MHz, the barrier to internal rotation of the two methyl groups is V3 = 1.1752 kJ/mol, their moments of inertia were found to be Iα = 3.0808(9) uÅ2 . The nitrogen nuclear quadrupole constants are χaa = +1.600(5) MHz, χbb = -4.572(3) MHz and χcc = +2.972(5) MHz.

Ab initio studies on amides: conformational preferences of diacetamide and barriers to interconversion of the conformers

1980 ◽  
Vol 33 (11) ◽  
pp. 2337 ◽  
Author(s):  
L Radom ◽  
NV Riggs
Keyword(s):  
Hydrogen Atom ◽  
Ab Initio ◽  
Internal Rotation ◽  
Model Systems ◽  
Methyl Groups ◽  
Electrostatic Repulsion ◽  
Conformational Preferences ◽  
Out Of Plane ◽  
Model Transition ◽  
Good Agreement

Diacetamide, like other diacylamines, is capable of existing in three basic conformations about the N-C bonds. Optimization (STO-3G) of model systems in which all first-row atoms and the amido hydrogen atom are held coplanar predicts that the E,Z conformer (3) is of lowest energy, the Z,Z conformer (2) of somewhat higher energy (4.2 kJ mol-1), and the E,E conformer (1) of highest energy (23.6 kJ mol-1); 4-31G evaluation of the energies suggests that (1) and (2) are each of higher energy than (3) by 27-28 kJ mol-1. It is suggested that (2) is destabilized with respect to (3) by electrostatic repulsion of the two negatively charged oxygen atoms whereas destabilization of (1) is due to substantial methyl-methyl steric interactions as reflected in the very wide <CNC (136°); the energy of (1) is, however, raised by out-of-plane or rotational movements of the methyl groups, i.e., the preferred structure (excluding methyl hydrogens) is planar. The calculated height of the barrier to internal rotation of (3) by either of two model transition states is 41-45 kJ mol-1, in good agreement with an experimental value of 45.2 kJ mol-1 in solution at -60°.

scholarly journals Multiblock Analysis Applied to TD-NMR of Butters and Related Products

2020 ◽  
Vol 10 (15) ◽  
pp. 5317
Author(s):  
Jean-Michel Roger ◽  
Silvia Mas Garcia ◽  
Mireille Cambert ◽  
Corinne Rondeau-Mouro
Keyword(s):  
Solid Phase ◽  
Fat Content ◽  
Prediction Errors ◽  
Chemometric Methods ◽  
Covariance Selection ◽  
T1 Relaxation ◽  
Repeatability Error ◽  
Measurement Protocol ◽  
Relaxation Measurements ◽  
Better Than

This work presents a novel and rapid approach to predict fat content in butter products based on nuclear magnetic resonance longitudinal (T1) relaxation measurements and multi-block chemometric methods. The potential of using simultaneously liquid (T1L) and solid phase (T1S) signals of fifty samples of margarine, butter and concentrated fat by Sequential and Orthogonalized Partial Least Squares (SO-PLS) and Sequential and Orthogonalized Selective Covariance Selection (SO-CovSel) methods was investigated. The two signals (T1L and T1S) were also used separately with PLS and CovSel regressions. The models were compared in term of prediction errors (RMSEP) and repeatability error (σrep). The results obtained from liquid phase (RMSEP ≈ 1.33% and σrep≈ 0.73%) are better than those obtained with solid phase (RMSEP ≈ 5.27% and σrep≈ 0.69%). Multiblock methodologies present better performance (RMSEP ≈ 1.00% and σrep≈ 0.47%) and illustrate their power in the quantitative analysis of butter products. Moreover, SO-Covsel results allow for proposing a measurement protocol based on a limited number of NMR acquisitions, which opens a new way to quantify fat content in butter products with reduced analysis times.

Determination of a High Barrier Hindering Internal Rotation from the Ground State Spectrum. The Methylbarrier of Propane

1985 ◽  
Vol 40 (3) ◽  
pp. 271-273 ◽  
Author(s):  
G. Bestmann ◽  
W. Lalowski ◽  
H. Dreizler
Keyword(s):  
Fine Structure ◽  
Internal Rotation ◽  
Ground State ◽  
Methyl Groups ◽  
Rotational Spectrum ◽  
Rotation Barrier ◽  
Rotation Axes ◽  
Internal Rotation Barrier ◽  
The Moment

The internal rotation barrier V3, the moment of inertia Iα of the methyl tops and the angle between the two internal rotation axes were determined from the torsional fine structure of the rotational spectrum in the torsional ground state. A tilt angle of 1.4° of the methyl groups toward each other results.

Sign in / Sign up

Export Citation Format

Share Document